Non-transformed Breast Epithelial Cells Research Articles

Abstract PO5-08-06: Metabolic shift to serine pathway induced by lipids confers oncogenic properties in non-transformed breast cells

Abstract Introduction. Oncogenic factors that are local/in-breast are of great interest as they may be more specifically targetable for breast cancer prevention than systemic factors. We have identified a lipid metabolism gene signature that is enriched in breast tissue at risk for estrogen negative breast cancer (ER- BC). Utilizing the medium chain fatty acid Octanoic acid (OA) to probe lipid metabolism in non-transformed breast epithelial cells, we observed increased flux through several metabolic reactions and altered histone methylation with consequent changes in gene expression (e.g. neural genes). Neuronal signaling and regulatory circuits are observed in cancer cells of multiple origins, not just ones with ontological relationships to neurons. We hypothesize that the first and rate limiting step in the de novo serine pathway, which is catalyzed by Phosphoglycerate Dehydrogenase (PHGDH) is key to these observations. In the forward direction, PHGDH participates in the serine, one-carbon, glycine (SOG) and methionine pathways that produce the methyl donor S-adenosylmethionine (SAM) and in the reverse direction produces the oncometabolite 2-Hydroxyglycerate (2-HG). Methods. Non-transformed MCF-10A cells exposed to OA were utilized for U13C-glucose tracing. SAM and 2-HG concentrations following treatment with OA ± PHGDH inhibitor were measured by liquid chromatography. CUT&RUN for H3K4me3 was performed and genes affected by OA (PMID: 28263391) were compared with OA-responsive peaks. Single cell RNA-sequencing was carried out using breast microstructures derived from reduction mammoplasty tissue exposed to vehicle or OA. Microstructures were dissociated into single cells and sequenced using the 10x Genomics platform. The digital expression matrix file containing UMIs were analyzed with Seurat. Alkaline comet assay was performed to detect DNA breaks. Results. U13C-glucose tracing in presence of OA revealed that one-carbon-THF was redirected to the methionine cycle increasing flux to methylation. Concentrations of SAM and 2-HG increased after 15- and 30-min OA exposure, respectively; PHGDH inhibitor blocked these increases. H3K4me3 CUT&RUN revealed 661 differential peaks (FDR < 0.05) comparing OA to control. 73% of H3K4me3 OA-associated peaks were in regulatory regions of OA-induced genes (FDR < 0.01), these genes are involved in neural pathways, EMT and ER- BC. Motif analysis revealed an overrepresentation of binding sites for transcription factors ATF3/4 (p < 0.05), which are regulators of the serine pathway. Single cell RNA-sequencing revealed OA not only affected the distribution of cell subpopulations but also modulated the expression of many genes within each subcluster. The percentage of luminal progenitor subcluster 3 increased upon OA from less than 1% to about 13%. Within basal subcluster 3, OA drives the expression of ATF3, along with two of the enzymes in the de novo serine pathway: PHGDH and PSAT1. Alkaline comet assay showed DNA breaks in OA- and control 2-HG- treated cells. Conclusions. Metabolism of OA in preference to glucose and glutamine results in a metabolic shift toward the serine pathway increasing the production of SAM and 2-HG, with implications for oncogenesis: 1. SAM production results in epigenetic fostered plasticity leading to reprogramming/selecting cells that express genes consistent with a neural/neural crest-like state. These co-opted neuronal regulatory mechanisms can make critical contributions to the acquired functional capabilities that drive cancer development. 2. 2-HG exposure results in appearance of DNA breaks, which are likely consequent to the inhibition of the alpha-ketoglutarate-dependent dioxygenases KDM 4A/B by 2-HG. Their catalytic activity is required for homologous recombination repair; inhibition results in metabolic “BRCAness”. Citation Format: Mariana Bustamante Eduardo, Gannon Cottone, Shiyu Liu, Maria Paula Zappia, Elizaveta V. Benevolenskaya, Abul Bashar Mir Md. Khademul Islam, Maxim V. Frolov, Seema Khan, Susan Clare. Metabolic shift to serine pathway induced by lipids confers oncogenic properties in non-transformed breast cells [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-08-06.

Abstract 4744: Epigenetic reprogramming induced by lipids fosters mammary cell plasticity in non-transformed breast epithelial cells

Abstract Introduction. Lipid exposure of non-transformed breast epithelial cells results in increased flux modifications, and profound changes in gene expression. The upregulated genes are involved in stemness, neural development, and neural crest pathways. Neural genes are highly expressed in an estrogen receptor negative breast cancer (ERnegBC): the triple negative subtype. We aim to identify mechanisms that link lipids and epigenetic reprogramming to the genesis of ERnegBC. Methods. Non-transformed MCF-10A cells exposed to octanoic acid (OA) were utilized for U13C-glucose tracing. S-adenosylmethionine (SAM), 2-HG and other metabolites were analyzed following treatment with OA ± PHGDH inhibitor. CUT&RUN for H3K4me3 and H3K27me3 was performed, and genes affected by OA (PMID: 28263391) were compared with OA-responsive peaks. OA-induced genes with CUT&RUN peaks were measured in breast organoids derived from reduction mammoplasty samples exposed to OA. The Aldefluour assay was used to identify stem-like (ALDH+) cells. Results. U13C-glucose tracing in presence of OA showed decreased glucose uptake, glycolysis and pentose phosphate pathway flux, with little effect on the TCA cycle. One-carbon (1C)-THF was redirected to the methionine cycle increasing flux to methylation. The methyl donor SAM and the demethylase inhibitor 2-HG increased after 15- and 30-min OA exposure, respectively; PHGDH inhibitor blocked these increases likely via effects on 1C metabolism. H3K4me3 CUT&RUN revealed 661 differential peaks (FDR < 0.05) comparing OA to control. The genes associated with these peaks are involved in neuron differentiation, neural crest, EMT and neural genes expressed in ERnegBC. 73% of H3K4me3 OA-associated peaks were in regulatory regions of OA-induced genes (FDR < 0.01), including NGFR (log2FC = 11.7), NGF (log2FC = 8), NTRK1 (log2FC = 2.1). OA-induced genes with enriched H3K4me3 peaks were also upregulated in breast organoids exposed to OA, such as NGFR (FC = 2.2), NGF (FC = 4.7), NTRK1 (FC = 6.6). Motif analysis revealed an overrepresentation of transcription factors (p < 0.05) associated with EMT (Zeb1, Slug), neural functions (E2A, AP1, JunB), neuronal-injury (Atf3) and stress response (Chop, Atf4). Twelve H3K27me3 peaks were enriched in control (FDR < 0.05) and associated with increased gene expression in OA, among them were LGR6 (log2FC = 1.9), a gene associated with ERnegBC and PLAG1 (log2FC = 2.8) a stem cell marker. ALDH+ cells’ percentage increased by at least 10% after OA exposure. Conclusions. Lipid exposure affects the production of SAM and 2-HG, which results in epigenetic fostered plasticity, leading to reprogramming/selecting cells with a multi-potential embryonic or stem-like state and/or differentiation to a neural/neural crest-like state which may facilitate ERnegBC genesis. Citation Format: Mariana Bustamante Eduardo, Gannon Cottone, Shiyu Liu, Seema Khan, Susan Clare. Epigenetic reprogramming induced by lipids fosters mammary cell plasticity in non-transformed breast epithelial cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4744.

Abstract P6-11-03: Lipid-rich environment induces epigenetic reprogramming in non-transformed breast epithelial cells enhancing a mammary cell plasticity

Abstract Introduction. The identification of women specifically at risk for estrogen receptor negative breast cancer (ER- BC) and the targeted treatment of this disease are significantly unmet clinical needs. We analyzed the gene expression profiles of epithelial cells from the contralateral unaffected breasts (CUBs) of BC patients and identified a lipid metabolism gene signature enriched in the CUBs of women with ER- BC (PMID: 28263391). Subsequently, we observed that exposure of non-transformed breast epithelial cells to lipids results in significant changes in gene expression and histone posttranslational modifications; and increased flux through multiple metabolic reactions, including those of serine and methionine (PMID: 35508495). Interestingly, the upregulated genes are involved in neural development, axon guidance, neural crest pathways and stemness. Neural genes are highly expressed in Triple Negative Breast Cancers (TNBCs) especially in the C2 cluster. Given that mammary stem/progenitor cells have distinct metabolic properties compared to other mammary cell subsets, we hypothesized that upon lipid exposure, stem-like cells have a survival advantage, and that lipid induces epigenetic reprogramming into neural-like cells which may foster a malignant transformation. Methods. To interrogate potential mechanisms linking lipids and epigenetic reprogramming, we performed CUT&RUN for H3K4me3 and H3K27me3 in non-transformed, estrogen and progesterone receptor negative MCF-10A cells cells exposed to vehicle or octanoic acid (OA) for 24 hrs. Peaks were called using MACS2 and differential peaks identified with DiffBind. Differentially expressed genes affected by OA (PMID: 28263391) were compared with target genes from the CUT&RUN. To determine the contribution in OA exposed cells of serine and methionine metabolism to S-adenosyl methionine (SAM), 13C-glucose tracing was performed. The Aldefluour assay was used to identify stem-like (ALDH+) cells in lipid-exposed MCF-10A cells. To determine if lipid-exposed cells adopt a neural-like phenotype, MCF-10A cells were grown on Poly-D-Lysine/Laminin (PDL/LM) coated plates. Results. A total of 661 differential peaks were identified for H3K4me3 (FDR < 0.05) encompassing TNBC C2 markers (NRTN, CHRM3) and genes involved in neuron differentiation, axonogenesis (NGFR, NGF, FOXA2), neural crest migration (NTRK2, MMP2) and EMT (DLL4, MMP15). Approximately 73% of H3K4me3 OA-associated peaks encompass regulatory regions of genes that experienced a significant increase in gene expression with OA exposure (FDR < 0.01), including NGFR (log2 FC = 11.7), FOXA2 (log2 FC = 11.6), NGF (log2 FC = 8). Twelve H3K27me3 peaks were significantly enriched in vehicle (FDR < 0.05) and associated with increased gene expression in OA, among them were the stem cell markers LGR6 (log2 FC = 1.9) and PLAG1 (log2 FC = 2.8). 13C stable isotope tracing revealed that in presence of OA, glucose contributes to increased fractional abundance of the SAM M+1 isotopologue (adj p = 0.003) indicating that carbons derived from the serine synthesis pathway are used for re-methylation of homocysteine to methionine. Vehicle treated cells growing on PDL/LM plates assumed an epithelial phenotype while OA-treated cells adopted a neurite-like phenotype. Upon OA treatment the percentage of ALDH+ cells increased by a minimum of 10%. Conclusions. The increase of fractional abundance of SAM and the upregulation of neural genes regulated by H3K4me3 as well as the enrichment of ALDH+ cells and the development of a neural-like phenotype in a rich lipid environment, suggests that lipid exposure affects the production of SAM, which results in epigenetic fostered plasticity, leading to reprogramming/selecting cells with a multi-potential embryonic or stem-like state and/or differentiation to a neural/neural crest-like state. Citation Format: Mariana Bustamante Eduardo, Gannon Cottone, Seema Khan, Susan Clare. Lipid-rich environment induces epigenetic reprogramming in non-transformed breast epithelial cells enhancing a mammary cell plasticity [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-11-03.

Abstract P6-11-08: Non-transformed breast epithelial cells show neural-like gene signature after lipid exposure

Abstract Introduction: The identification of women specifically at risk for estrogen receptor negative breast cancer (ER-BC) and the targeted treatment of this disease are significantly unmet clinical needs. To that end, we analyzed the gene expression profiles of epithelial cells from the contralateral unaffected breasts (CUBs) of BC patients and identified a lipid metabolism gene signature, which was enriched in the CUBs of women with ER-negative BC (PMID: 28263391). Subsequent experiment revealed that exposure of non-transformed breast epithelial cells to lipid results in significant changes gene expression, chromatin accessibility and histone posttranslational modifications (PMID: 35508495). Several of the upregulated genes are hallmarks of the various fates of vagal neural crest: Neural, neurogenic and mesenchymal lineages. We hypothesize that lipid exposure imparts a survival advantage of stem-like cells, that lipid-induced epigenetic changes lead to a neural crest-like transcription signature and that these genes are not expressed normally in the breast. Methods: MCF10A cells were exposed to vehicle or octanoic acid (OA) for 24 hours. Gene expression was assayed by RNA-seq and OA responsive genes were identified (PMID: 35508495). Single-cell RNA sequencing (scRNA-seq) data from 14 human reduction mammoplasties (RM) was obtained from a publicly accessible data set (PMID: 34031589). The scRNA data was clustered and identified by unsupervised clustering (Seurat, v3.4.1) using cell-type markers curated using Supplementary table 2 from (PMID: 34031589). The bulk RNA-seq data from the OA treated cells was deconvoluted to cell-lineages using Bisque. The most significant upregulated VNC neural/neuronal/mesenchymal genes from the gene expression analysis were then plotted on the lineage clusters using FeaturePlot to determine if these markers are found in the normal breast epithelium, or other cell lineages. The plots were then filtered and re-clustered to look at basal-luminal cell types only. We utilized a second resource, a web-application for snATAC-seq data from various stages of mouse mammary development developed by the Wahl lab (https://wahl-lab-salk.shinyapps.io/Mammary_snATAC/), to query these same genes. Results: Deconvolution of the bulk RNA-sequencing data revealed a transition to a pericyte transcription program following exposure to OA. Nerve growth factor (NGF) was found to be expressed in pericytes while nerve growth factor receptor (NGFR) was found within the basal epithelial cell lineage. Genes overexpressed in the VNC neural cluster and overexpressed in the OA-exposed MCF10 cells, PPP1R1C (2.39x, adj p=1.6E-5), FOXD3 (6.7x, adj p=6.7E-10), DIO3 (5.9x, adj p=3.9E-6) and MOXD3 (4.2x, adj p=1.5E-23) all evidence little to no expression in the normal breast but are observed in murine fetal mammary stem cells. Schwann cell precursor (SCP) markers, CDH19 and ROPN1, significantly upregulated in OA treated cells: 5.4x and 1.6x, respectively, exhibited low expression in luminal progenitors but in the mouse were observed in the mammary stroma. CDH19, a gene exclusive to SCPs, is expressed in stroma following murine birth. PRRX1, a key regulator of the VNC mesenchymal cell fate cluster, is 9.3-fold (p adj=4.9E-49) overexpressed in the OA treated cells, expressed strongly in pericytes and stroma and to a lesser extent in basal epithelial cells of the normal human breast and stroma of the murine mammary gland. Conclusions: Treatment of non-transformed mammary epithelial cells with lipid, specifically OA, shows significant upregulation of multiple VNC genes associated with both neural and mesenchymal fate. scRNA-seq from RM patients reveals that many of these same markers are either found in non-epithelial cell clusters or are found with low expression in luminal mammary lineages (both progenitors and mature). Citation Format: Gannon Cottone, Mariana Bustamante Eduardo, Shivangi Yadav, Seema Khan, Susan Clare. Non-transformed breast epithelial cells show neural-like gene signature after lipid exposure [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-11-08.

Abstract 3024: Lipid treatment induces a neural-like phenotype in non-transformed breast epithelial cells

Abstract Introduction. Genes involved in lipid metabolism have been shown to be overexpressed in the contralateral unaffected breast of women with estrogen receptor negative (ER-) breast cancer (BC) (PMID: 28263391). Exposure of non-transformed MCF10A breast epithelial cells to lipids results in altered chromatin structure, epigenomic reprogramming and changes in gene expression. Within the upregulated genes are numerous gene sets related to nervous system development, neurons and synapses. Neural genes are more highly expressed in Triple Negative Breast Cancers (TNBC) compared to non-TNBC, and several studies have shown a connection between neural stemness and tumorigenicity. We hypothesized that stem-like cells have a survival advantage when exposed to lipids and that lipid-induced molecular changes underlying malignant transformation are connected with a neural-like phenotype. Methods. To validate the association of lipids and neural genes, a second non-transformed, estrogen and progesterone receptor negative breast epithelial cell line, MCF12A, was exposed to vehicle or octanoic acid (OA) for 24 hours. Gene expression was assayed by RNA-seq and OA responsive genes were identified. Gene set enrichment analysis was utilized to identify gene sets affected by OA. The 954 neural genes identified to be upregulated in TNBC (PMID: 32080331) were compared to OA responsive genes in both cell lines. The Aldefluor assay was used to identify stem-like (ALDH+) cells in vehicle and OA treated MCF10A cells. To determine if lipid-exposed cells adopt a neural-like phenotype, MCF10A cells were grown on Poly-D-Lysine/Laminin (PDL/LM) coated plates. Results. 5,684 and 5,305 genes were up- and down-regulated (FDR < 0.01), respectively, in MCF12A OA treated cells. Numerous gene sets were significantly associated with OA exposure, including many neural-related pathways. More than 50% of the gene sets identified following OA-exposure were common to both cell lines. 418 and 303 neural genes upregulated in TNBC were significantly (FDR < 0.01) upregulated after OA treatment in MCF10A and MCF12A, respectively. Cells growing on PDL/LM plates assumed the normal MCF10A phenotype in presence of vehicle while OA-treated cells adopted a neuronal-like phenotype. Upon OA treatment the percentage of ALDH+ cells increased by a minimum of 10%. Conclusions. OA treatment was associated with the enrichment of ALDH+ cells, expression of neuronal-related genes and the development of neural-like phenotype. The upregulation neural genes upregulated in TNBC upon OA treatment may in part explain the association of lipid exposure and ER- BC. The upregulation of neural-related genes, and the development of neural-like phenotype suggests that lipid exposure results in cell state instability or plasticity, leading to reprogramming/selecting cells with a multi-potential embryonic or stem-like state that has been associated with tumor progression. Citation Format: Mariana Bustamante Eduardo, Shivangi Yadav, Seema Khan, Susan Clare. Lipid treatment induces a neural-like phenotype in non-transformed breast epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3024.

Abstract P5-05-05: Unraveling the mechanism of Lipid-induced malignant transformation in non-transformed breast epithelial cells

Abstract Introduction. With the goal of defining the in-breast environment that facilitates the development of estrogen receptor negative (ER-) breast cancer (BC), we have previously identified a set of genes involved in lipid metabolism with increased expression in the contralateral unaffected breast of women with ER- BC (PMID: 28263391). MCF-10A cells exposed to lipids in vitro display profound changes in gene expression, chromatin packing density, chromatin accessibility and histone posttranslational modifications (PTMs). In addition, flux through thirty-eight metabolic reactions was significantly increased by this exposure, including those of the electron transport chain (ETC). However, the mechanisms by which lipids induce molecular changes that result in epigenomic reprogramming, and potentially promote malignant transformation remain to be elucidated. We hypothesized that dysfunction of the ETC and increased serine, glycine, one carbon (SGOC) metabolism pathway activity play a role in the modulation of epigenetics. Methods. To interrogate potential mechanisms that link lipids to ER- BC genesis, estrogen and progesterone receptor negative MCF-10A cells were cultured in MEBM/MEGM and exposed to vehicle, octanoic acid (C8) or linoleic acid (C18) for 24 hours. Histone PTMs were assayed by liquid chromatography-mass spectrometry. Gene expression was measured by RNA-seq and differentially expressed genes between vehicle and lipid treated groups were identified using the DESeq2 R package. ATAC-seq was performed to study chromatin accessibility. MCF-10A cells were exposed to C8 in presence or absence of inhibitors of Complex I (Metformin) and Complex III (Antimycin A) of the ETC. Real-time qPCR was performed to measure epigenetic modulators, Unfolded Protein Response (UPR) pathway and SGOC metabolism genes. Results. Histone PTMs changed significantly following 24 hours exposure to C8 or C18. Exposure to C8 resulted in the modulation of the expression of genes involved in the UPR/recognition of mitochondrial dysfunction (ATF4), de novo serine biosynthesis (PHGDH, PSAT1, SPH) and one-carbon metabolism (SHMT2, MTHFD2) pathways as well as numerous genes coding for epigenetic modulators. Upon C18 exposure, the binding motif for ATF4 was among the most significantly enriched motifs in the open chromatin regions and p53 was among the motifs with significantly decreased accessibility. Interestingly ATF4 actives PHGDH expression while p53 suppresses it. Exposure to C8 in presence of ETC inhibitors affected gene expression in the same direction as lipid exposure and co-treatment had an additive effect. Fatty acid oxidation and inhibition of the ETC increased the expression of PHGDH: C8, 2.6-fold (p-value = 0.005); Metformin, 2.3-fold (p-value = 0.0052); Antimycin A, 5.1-fold (p-value < 0.0001); C8 plus Metformin, 5.3-fold (p-value < 0.0001), and C8 plus Antimycin A, 5.2-fold (p-value < 0.0001). Conclusions. The modulation of epigenetic effectors does not appear to be a consequence of increased flux through the ETC but rather a consequence of increased SGOC metabolism, and the methionine cycle. Our in vitro model shows that lipid-induced stress increases ATF4 expression. ATF4 controls the expression of PHGDH, PSAT1, SPH, SHMT2 and MTHFD2 which influences epigenetics through S-adenosyl methionine production, the major methyl donor. PHGDH overexpression appears to be the key in our model as it has been associated with ER- BC and its engineered overexpression in non-transformed breast cells causes alterations associated with malignant transformation. The increase in PDGDH expression is hypothesized to compensate for mitochondrial dysfunction and to restore redox homeostasis by producing precursors that can be used for the production of antioxidants, such as glutathione. Citation Format: Mariana Bustamante Eduardo, Shivangi Yadav, Seema Khan, Susan Clare. Unraveling the mechanism of Lipid-induced malignant transformation in non-transformed breast epithelial cells [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-05-05.

Abstract 2296: Regulation of P-body dynamics and formation in tumors through EDC3 phosphorylation by PIM and AKT

Abstract Processing bodies (P-bodies) are cytoplasmic mRNA granules that form a hub to regulate mRNA translation via controlling decapping, degradation, and storage. P-bodies markedly increase as part of a stress response for example during nutrient deprivation and hypoxia. Thus, P-bodies could regulate cell fate by tuning protein levels during the stress, and thereby contribute to tumor initiation, growth, and metastasis. However, it is unclear how P-body formation is regulated by these stress and what biologic pathways P-body controls. Dysregulation of PIM and AKT kinases has been found in multiple cancers, including prostate and breast cancers. We find that the protein Enhancer of mRNA-decapping Protein 3 (EDC3), a P-body component, binds with the PIM protein kinase and is phosphorylated on serine 161 by the PIM and AKT kinases, suggesting these kinases could regulate P-body formation and function. Thus, we hypothesize that these oncogenic kinases regulate the EDC3 activity and P-body function via the phosphorylation of EDC3. Suppression of EDC3 phosphorylation by inhibiting PIM and AKT activities with drugs leads to an increase in P-body number. A knock-in mutation substituting alanine for serine 161 in PC3-LN4 prostate cancer cell line inhibited growth, migration and invasion in vitro. Prostate cancer tumor growth in these cells containing EDC3 mutation was reduced in mouse xenograft model, suggesting that this single phosphorylation is essential for regulating cell growth. These results suggest that the level of specific RNAs and its translation is being controlled by this mutation. Indeed, integrin family proteins, ITGB1 and ITGA6, are shown to be decreased in these cells consistent with the inability of these cells to attach and invade. High levels of phosphorylated EDC3 were detected in the breast cancer cell lines tested, whereas non-transformed immortalized breast epithelial cell lines showed much lower EDC3 phosphorylation. IHC staining of human breast cancer samples with phospho-specific antibodies demonstrated that EDC3 was highly phosphorylated in contrast to normal breast tissue which demonstrated low level of phosphorylation. These data indicate that in tumors, breast and prostate cancer, with activated PIM and AKT, high phosphorylation of EDC3 would increase the translation of target mRNAs via reducing their storage and destruction and affecting tumor cell growth and motility. Therefore, the phosphorylation of EDC3 by Pim and AKT kinases can be a driver of malignancy by controlling mRNA levels in breast and prostate cancers. Citation Format: Jeremiah Bearss, Sathish K. Padi, Neha Singh, Marina Cardo-Vila, Andrew S. Kraft, Koichi Okumura. Regulation of P-body dynamics and formation in tumors through EDC3 phosphorylation by PIM and AKT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2296.

Long-term exposure to triclosan increases migration and invasion of human breast epithelial cells in vitro.

Extensive use of triclosan (2,4,4′‐trichloro‐2′‐hydroxydiphenyl ether) as an antimicrobial agent in household and personal care products has resulted in global exposure of the human population. Its presence in human tissues, including milk, and its oestrogen‐disrupting properties raise concerns for an involvement in breast cancer. Because metastatic tumour spread is the main cause of breast cancer mortality, we have investigated the effects of triclosan on cell migration and invasion using three human breast epithelial cell lines and using concentrations comparable with those in human tissues. Long‐term exposure to 10−7 M of triclosan resulted in increased migration and invasion as measured by xCELLigence technology for all three cell lines, for the immortalized but nontransformed MCF‐10F breast epithelial cells (after 28 weeks), the oestrogen‐responsive MCF‐7 breast cancer cells (after 17 weeks) and the oestrogen‐unresponsive MDA‐MB‐231 breast cancer cells (after 20 weeks). The effects were therefore not limited to cancerous cells or to oestrogen‐responsive cells. This was paralleled in the MCF‐10F and MCF‐7 (but not MDA‐MB‐231) cells by a reduction in levels of E‐cadherin mRNA as measured by reverse transcription–polymerase chain reaction (RT‐PCR) and of E‐cadherin protein as measured by western immunoblotting, suggesting a mechanism involving epithelial‐to‐mesenchymal transition. This adds triclosan to the increasing list of ingredients of personal care products that can not only enter human breast tissue and increase cell proliferation but also influence cell motility. If mixtures of components in household and personal care products contribute to increasing cell migration and invasion, then reduction in exposure could offer a strategy for reducing breast cancer spread.

Abstract P3-06-14: Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim

Abstract Background/Rationale: While some patients with triple negative breast cancer (TNBC) achieve long-term remission with standard-of-care chemotherapy, many have cancers that are chemotherapy resistant, putting them at risk for metastatic recurrence. There is also a lack of targeted therapies for TNBC, highlighting the need for novel therapeutic strategies for this subtype. PRKCQ, a member of the novel protein kinase C family, is preferentially expressed in TNBC compared to other breast cancer subtypes and we previously reported that PRKCQ expression is sufficient to promote oncogenic activities (growth-factor independent growth, anoikis resistance and migration). In addition, PRKCQ suppression inhibits growth of TNBC tumor xenografts. We sought to determine if PRKCQ expression modulation impacts sensitivity of triple negative breast cancer cells to standard of care chemotherapy and whether PRKCQ inhibition could be a strategy to enhance chemosensitivity of drug-resistant TNBC. Methods: We determined the effects of modulating PRKCQ expression, using PRKCQ cDNA or shRNA vectors, on sensitivity of TNBC cells to the apoptotic effects of standard-of-care chemotherapy, including those cancers that are relatively chemotherapy resistant at baseline. We also determined the mechanisms by which PRKCQ regulates sensitivity to chemotherapy. Results: Increased PRKCQ expression in non-transformed MCF-10A breast epithelial cells promotes resistance to the apoptosis-inducing effects of Doxorubicin or Paclitaxel treatment. These effects are dependent on PRKCQ kinase activity as a catalytically inactive PRKCQ failed to promote resistance. Downregulation of PRKCQ or inhibition of its kinase activity enhanced sensitivity of TNBC cells to chemotherapy. PRKCQ impacts chemotherapy sensitivity of TNBC by regulating epithelial-mesenchymal transition (EMT) and expression of Bim, a pro-apoptotic Bcl2 family protein. Conclusions. PRKCQ promotes resistance of TNBC to standard of care chemotherapies by promoting EMT and suppressing pro-apoptotic Bim. Inhibiting PRKCQ expression or activity sensitizes TNBC cells to chemotherapy and could be an effective strategy to overcome chemotherapy resistance of a subset of triple negative breast cancers, thereby improving patient outcomes. Citation Format: Hanna Yoko Irie, Jessica H. Byerly, Elisa R. Port. Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-06-14.

NF-κB/NKILA signaling modulates the anti-cancerous effects of EZH2 inhibition.

A wealth of evidence supports the broad therapeutic potential of NF‐κB and EZH2 inhibitors as adjuvants for breast cancer treatment. We contribute to this knowledge by elucidating, for the first time, unique regulatory crosstalk between EZH2, NF‐κB and the NF‐κB interacting long non‐coding RNA (NKILA). We define a novel signaling loop encompassing canonical and non‐canonical actions of EZH2 on the regulation of NF‐κB/NKILA homeostasis, with relevance to breast cancer treatment. We applied a respective silencing approach in non‐transformed breast epithelial cells, triple negative MDA‐MB‐231 cells and hormone responsive MCF‐7 cells, and measured changes in EZH2/NF‐κB/NKILA levels to confirm their interdependence. We demonstrate cell line‐specific fluctuations in these factors that functionally contribute to epithelial‐to‐mesenchymal transition (EMT) remodelling and cell fate response. EZH2 inhibition attenuates MDA‐MB‐231 cell motility and CDK4‐mediated MCF‐7 cell cycle regulation, while inducing global H3K27 methylation and an EMT phenotype in non‐transformed cells. Notably, these events are mediated by a cell‐context dependent gain or loss of NKILA and NF‐κB. Depletion of NF‐κB in non‐transformed cells enhances their sensitivity to growth factor signaling and suggests a role for the host microenvironment milieu in regulating EZH2/NF‐κB/NKILA homeostasis. Taken together, this knowledge critically informs the delivery and assessment of EZH2 inhibitors in breast cancer.

PO-286 Protein kinase D3: a crucial regulator of breast cancer stem cell survival

IntroductionTriple negative breast cancer (TNBC) accounts for 15%–20% of all breast carcinomas in women. TNBC is particularly aggressive, highly metastatic and associated with poor prognosis. We previously identified Protein Kinase D3 (PKD3) to be upregulated in TNBC. PKD3 is a serine-threonine kinase that is best known for its functions in membrane trafficking and actin remodelling. Here we identify a novel role for PKD3 in breast cancer stem cell (CSC) maintenance. CSCs are endowed with tumor-initiating capacity, they possess increased chemoresistance and are known to initiate metastasis, and therefore are responsible for tumour relapse.Material and methodsIn the TNBC cell line MDA-MB-231 with a stable PKD3 knockdown, we performed a flow cytometry based screen of cell surface proteins, revealing the downregulation of several membrane proteins associated with CSCs. The importance of PKD3 for driving a CSC gene expression signature, maintaining CSC numbers and function was tested by qRT-PCR analysis of CSC markers, by measuring aldehyde dehydrogenase (ALDH) activity and performing mammosphere assays, respectively. Paclitaxel sensitivity of TNBC cell lines was assessed in combination with the selective PKD inhibitor CRT0066101. Whether the ectopic expression of PKD3 was sufficient to induce the expansion of the CSC pool was analysed in the non-transformed breast epithelial cell line MCF10A.Results and discussionsIn MDA-MB-231 cells with PKD3 knockdown, the CSC markers (CD184, Notch4, Sox2, Oct3/4) were downregulated. This was associated with reduced CSC numbers based on ALDH positivity and sphere-forming efficiency in mammosphere assays. Pharmacological PKD inhibition in the TNBC cell lines MDA-MB-231, BT549 and MDA-MB-436 verified these results. By contrast, inducible PKD3 expression in MCF10A cells elevated mammosphere formation and stem cell marker expression. Importantly, the combination of paclitaxel with CRT0066101 was superior over the single treatments in suppressing the survival of MDA-MB-231, BT549 and MDA-MB-436 cells in both colony formation and mammosphere assays.ConclusionOur results establish PKD3 as a crucial regulator of CSC maintenance and demonstrate that paclitaxel treatment in combination with PKD inhibition provides a potential novel strategy for future therapeutic applications in TNBC treatment.

Tropomyosin isoform Tpm2.1 regulates collective and amoeboid cell migration and cell aggregation in breast epithelial cells.

Metastasis dissemination is the result of various processes including cell migration and cell aggregation. These processes involve alterations in the expression and organization of cytoskeletal and adhesion proteins in tumor cells. Alterations in actin filaments and their binding partners are known to be key players in metastasis. Downregulation of specific tropomyosin (Tpm) isoforms is a common characteristic of transformed cells. In this study, we examined the role of Tpm2.1 in non-transformed MCF10A breast epithelial cells in cell migration and cell aggregation, because this isoform is downregulated in primary and metastatic breast cancer as well as various breast cancer cell lines. Downregulation of Tpm2.1 using siRNA or shRNA resulted in retardation of collective cell migration but increase in single cell migration and invasion. Loss of Tpm2.1 is associated with enhanced actomyosin contractility and increased expression of E-cadherin and β-catenin. Furthermore, inhibition of Rho-associated kinase (ROCK) recovered collective cell migration in Tpm2.1-silenced cells. We also found that Tpm2.1-silenced cells formed more compacted spheroids and exhibited faster cell motility when spheroids were re-plated on 2D surfaces coated with fibronectin and collagen. When Tpm2.1 was downregulated, we observed a decrease in the level of AXL receptor tyrosine kinase, which may explain the increased levels of E-cadherin and β-catenin. These studies demonstrate that Tpm2.1 functions as an important regulator of cell migration and cell aggregation in breast epithelial cells. These findings suggest that downregulation of Tpm2.1 may play a critical role during tumor progression by facilitating the metastatic potential of tumor cells.

Abstract 2326: A high-throughput screen identified cancer selective small molecules that kill independent of mitochondrial apoptosis

Abstract Triple negative breast cancer (TNBC) lacks expression of oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor 2 (HER2). Importantly, there have been fewer advances in the treatment of TNBC with the mainstay of treatment being cytotoxic chemotherapy. All too often though tumor responds poorly to chemotherapy, or relapse and resistance follow an initial response. We previously found in a range of hematological and solid tumors that chemoresistant cancers are far from the mitochondrial apoptotic threshold. To identify novel therapeutics for the treatment of chemoresistant breast cancer, we performed a high-throughput screen to identify small molecules that are cancer selective but can kill independent of the mitochondrial pathway of apoptosis. To perform this screen we used TNBC line MDA-MB-231 in which the pro-death proteins BAX/BAK were knocked down. BAX/BAK are essential for mitochondrial apoptosis. To enrich for compounds that were not non-specifically toxic, we simultaneously counter-screened against the non-transformed breast epithelial cell line MCF10a. We screened a total of 30,000 compounds in duplicate across the two cell lines. There was a hit rate of 0.3% in the screen and 85 compounds were retested in the validation cherry pick screen. From the cherry pick screen 18 compounds were further validated with low-throughput assessment for mitochondrial independent killing and selectivity for cancer cells. To identify the mechanism of action of the lead compound we used a genetic approach to generate an RNAi signature for the compound. This signature enables classification of the compound into known or novel class of compounds. The lead compound signature was most like that of histone deacetylase inhibitors (HDAC). Using an in vitro HDAC inhibitor screen, we identified that the compound selectively inhibited HDAC6. Importantly, we validated that the lead compound caused an increase in acetylated tubulin in cells, a target of HDAC6. In conclusion, we have identified a novel HDAC6 specific inhibitor that selectively kills cancer cells independent of mitochondrial apoptosis. Citation Format: Catriona M. Dowling, Micheal Hemann, James Bradner, Anthony Letai, Triona Ni Chonghaile. A high-throughput screen identified cancer selective small molecules that kill independent of mitochondrial apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2326. doi:10.1158/1538-7445.AM2017-2326

Abstract 4796: Chronic exposure to nitric oxide drives human breast epithelial cells to malignant-like features

Abstract The small endogenous signaling molecule, nitric oxide (NO) influences numerous physiological conditions including cancers. We have previously shown that different steady state NO levels activate pro-tumor signaling cascades. In this study, we explored the effect(s) of chronic NO exposure on breast epithelial cells as defined by changes in genomic stability, RNA and protein expression, and mostly importantly altered cell phenotype. Human breast epithelial cells (MCF10A) were chronically exposed to various concentrations of the NO donor DETA/NO for a three weeks. Distinct patterns of genomic alteration in the target genes (TP53, KRAS & PIK3CA) of exposed cells as compared to the background mutations were observed. In addition, quantitative real time PCR revealed increased expression of cancer stem cell (CSC) markers including NANOG, CD44, CXCR4 and OCT4 at 300 μM DETA/NO exposure. While altered cell morphology was observed in cells chronically exposed to 300-500 μM DETA/NO, increased motility occurred in cells cultured in 100 μM DETA/NO. Strikingly, these 100 μM NO-exposed cells grew in serum-free media; selected clonal populations as well as pooled cells formed colonies in soft agar that were disorganized and resembled cancer-like-clusters. In conclusion, these results implicate a precise tuning of microenvironmental NO levels that shift non-transformed breast epithelial cells toward cancerous phenotypes. The elucidation of underlying mechanisms may lend a new perspective regarding therapeutic approaches that redirect the cellular response(s) of tumor cells. Citation Format: Yuk Sing Robert Cheng, Stephen K. Anderson, Daniel W. McVicar, Daivd A. Wink, Lisa A. Ridnour. Chronic exposure to nitric oxide drives human breast epithelial cells to malignant-like features [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4796. doi:10.1158/1538-7445.AM2017-4796

Abstract 3954: Single-cell misregulation of NRF2 in basal-like breast cancer

Abstract Cancer is driven by a complex and heterogeneous combination of genes and pathways, many of which are not explicitly oncogenic on their own. These so-called non-oncogenes are required for maintenance of the tumorigenic state, but they are not mutated themselves. One way to identify “non-oncogene” pathways is to evaluate how proliferating cells adjust to variable and evolving environments. By examining heterogeneous transcriptional regulatory states of single cells in a 3D culture model of breast epithelial organization, we uncovered NRF2 as a candidate transcription factor upstream of an important regulatory state for morphogenesis. NRF2 is a known oncogene in lung cancer, but mutations in the transcription factor are uncommon in breast cancer. To examine the functional impact of NRF2 signaling, we engineered several triple-negative breast cancer cell lines with inducible short hairpin RNA to knock down NRF2. In claudin-low MDA-MB-231 cells, knockdown of NRF2 caused dramatic reduction in stellate invasion compared with shGFP control. In basal-like HCC-1806 cells, knockdown of NRF2 caused a reduction in “ruptured” tumorspheres, in which cells disseminate from their originating site. In a non-transformed breast epithelial cell line, overexpression of a non-degradable form of NRF2 caused greater variation in the size of acini, while knockdown of NRF2 narrowed the size distribution of acini. Therefore, knockdown of NRF2 substantially normalizes the size and shape of both non-transformed and cancerous 3D structures. We also analyzed expression levels of the genes in the provisional NRF2-regulated cluster after NRF2 knockdown or overexpression. Upon NRF2 knockdown, the p53-regulated transcripts CDKN1A (p21) and RPS27L were strongly induced, suggesting that p53 may be activated after NRF2 loss. Our results suggest a functional importance for NRF2 in multiple breast-epithelial and TNBC contexts, and raise the possibility of interplay between NRF2 and p53. A detailed understanding of NRF2 regulation and dynamics could enable new strategies to disrupt this non-oncogene addiction and re-sensitize cancer cells to their environment and to chemotherapy. Citation Format: Elizabeth Pereira, Kevin Janes. Single-cell misregulation of NRF2 in basal-like breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3954. doi:10.1158/1538-7445.AM2017-3954

Abstract P6-05-01: Low BRCA2 levels cause epigenetic activation of growth adaptive pathways without inducing recurrent genomic mutations

Abstract The development of therapeutics to prevent cancer onset is hindered by a lack of robust cell systems to study the earliest steps of malignant transformation. Significant barriers to studying cancer-initiating events include intrinsic cellular pathways to prevent cell proliferation in the setting of activating oncogenes or genomic instability. To circumvent this limitation, we studied in vitro transient depletion of breast cancer tumor suppressor genes followed by selective growth conditions to enrich for de novo mutations or stable epigenetic alterations that can confer a growth advantage to non-transformed breast epithelial cells. We report that transient BRCA2 depletion, but not depletion of other breast cancer genes, leads to a selective growth advantage in EGF-free media. This is due to a failure of BRCA2 inactivated cells to enact a mesenchymal-to-epithelial transition upon withdrawal of EGF. Genomic profiling and biochemical approaches indicate that transient loss of BRCA2 induces chromatin remodeling in concert with NF-κB signaling and histone H2B deacetylation to repress genes associated with the epithelial state. Notably, this process did not appear to require recurrent driver mutations, nor DNA methylation changes, but was dependent on ATR signaling. Overall, our work suggests that transiently low BRCA2 levels are sufficient to induce aberrant cell proliferation under certain conditions and that targeting epigenetic modifiers may be an approach to prevent BRCA2-induced malignancy. Citation Format: Gruber JJ, Snyder M. Low BRCA2 levels cause epigenetic activation of growth adaptive pathways without inducing recurrent genomic mutations [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-05-01.

Abstract A37: ‘Touch-and-go' behavior of cancer cells in spatially-confined, fiber-like microenvironments

Abstract In a crowded, fibrillar tumor microenvironment (TMEN), invading cancer cells encounter and interact with many other cells and cell types. Whether cancer cells stop migrating or reverse direction at every encounter with another cell, or circumnavigate and slide around the encounter, will affect the efficiency of the invasion process. We find that breast cancer cells migrating along fiber-like micropatterns (FLMs) respond differently to cell-cell encounters than what is expected based on the classically-established phenotype of contact-inhibition of locomotion (CIL). Cancer cells are remarkable efficient at sliding around other cancer cells, even along FLMs much narrower than their own cell body. In contrast, non-transformed breast epithelial cells reverse direction upon encountering other normal cells. Differences in cell size fail to predict these outcomes. Interestingly, the participation of normal cells in invasive sliding behavior increases when interacting with a cancer cell rather than another a normal cell. This induction of cancer-like behavior in normal cells suggests that heterotypic interactions between disparate cell types in the TMEN may produce synergistic, disease-promoting collective behaviors. Furthermore, using a series of individual and combinatorial genetic perturbations, we show that genetic factors (ErbB2, E-cadherin, PARD3, TGFbeta) quantitatively shift the ability of normal cells to slide. Specifically, successive genetic perturbations enable normal cells to slide on progressively narrower FLMs. These results suggest that as fibers align and mature during cancer progression, coincident genetic perturbations enable cells to take advantage of the widening fibrillar tracks to execute slides and achieve more efficient dispersion in a crowded microenvironment. Citation Format: Daniel Milano, Senthil Muthuswamy, Anand Asthagiri. ‘Touch-and-go' behavior of cancer cells in spatially-confined, fiber-like microenvironments. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr A37.

Differential response of normal and transformed mammary epithelial cells to combined treatment of anti-miR-21 and radiation

Purpose: MicroRNA miR-21 has emerged as a therapeutic target in the treatment of breast cancer. This study was designed to compare the responses of breast cancer cells and non-transformed breast epithelial cells to a combined regimen of miR-21 inhibition and radiation.Materials and methods: The MDA-MB-361 (breast cancer) and MCF-10A (non-transformed mammary epithelial) cell lines were used for the comparison in this in vitro study. The stable knockdown of miR-21 was performed by using lentiviral approach. The response of the cells was monitored 4, 24 and 48 h after the irradiation with 0.25 and 2.5 Gy, using sham-irradiated cells as controls. The response of the cells was established by performing various functional assays – cell viability and cell attachment, clonogenic survival, cell cycle analysis and 3D microtissue formation.Results: The knockdown of miR-21 induced significant increase in apoptosis and growth delay in MDA-MB-361 cancer cells compared to non-transformed MCF-10A cells. After combined radiation and anti-miR-21 treatment, MDA-MB-361 cells show reduced cell growth and viability what is presented in their inability to form colonies. MCF-10A cells were not as sensitive to the combined treatment and that has also been confirmed with colony forming assay.Conclusions: Cellular response to a combined treatment of anti-miR-21 and radiation is different between cancer and non-cancer cells which highly support the idea of linking miR-21 inhibitor and radiation treatment in the future therapeutic approaches for breast cancer.

Abstract B22: Novel dual regulation of epithelial-mesenchymal transition and anoikis resistance prevents metastases of triple negative breast cancer

Abstract Triple negative breast cancers (TNBC) are associated with a higher rate of metastatic recurrence and poorer prognosis due to intrinsic biological aggressiveness and lack of targeted therapies. Novel strategies to prevent metastasis are needed to improve outcomes for patients diagnosed with TNBC. Epithelial-mesenchymal transition (EMT) and anoikis resistance are processes recognized as contributing to treatment resistance and enhanced metastatic potential. In a functional genomic screen, we identified several candidates as novel dual regulators of EMT and anoikis sensitivity of triple negative breast cancer cells, that can be pharmacologically targeted to prevent metastases. One highly validated candidate, PTK6/Brk, specifically enhances anoikis resistance and metastatic potential of triple negative breast cancer cells via E-cadherin regulation. Overexpression of PTK6 in non-transformed immortalized breast epithelial cells is sufficient to promote an EMT, whereas PTK6 inhibition (either PTK6 shRNA or kinase inhibitor treatment) enhances E-cadherin expression and suppresses migration and lung colonization of TNBC cells. PTK6-dependent E-cadherin regulation and anoikis resistance is specifically dependent on levels of SNAIL, a transcriptional repressor. SNAIL down-regulation by PTK6 inhibition is directly responsible for modulation of anoikis sensitivity, which is in turn causally linked to lung colonization potential. PTK6 inhibition promotes the degradation of SNAIL via a novel mechanism independent of GSK3β and Fbox proteins known to regulate Snail ubiquitination. Using an siRNA screening approach, we identified novel E3 ligase candidates responsible for SNAIL ubiquitination and degradation downstream of PTK6 inhibition. PTK6 is a representative novel regulator of EMT and anoikis resistance that can be targeted to prevent metastases of patient triple negative tumors. Citation Format: Koichi Ito, Sun Hee Park, Anupma Nayak, Hanna Y. Irie. Novel dual regulation of epithelial-mesenchymal transition and anoikis resistance prevents metastases of triple negative breast cancer. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Targeting the Vulnerabilities of Cancer; May 16-19, 2016; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(1_Suppl):Abstract nr B22.

PRKCQ promotes oncogenic growth and anoikis resistance of a subset of triple-negative breast cancer cells.

BackgroundThe protein kinase C (PKC) family comprises distinct classes of proteins, many of which are implicated in diverse cellular functions. Protein tyrosine kinase C theta isoform (PRKCQ)/PKCθ, a member of the novel PKC family, may have a distinct isoform-specific role in breast cancer. PKCθ is preferentially expressed in triple-negative breast cancer (TNBC) compared to other breast tumor subtypes. We hypothesized that PRKCQ/PKCθ critically regulates growth and survival of a subset of TNBC cells.MethodsTo elucidate the role of PRKCQ/PKCθ in regulating growth and anoikis resistance, we used both gain and loss of function to modulate expression of PRKCQ. We enhanced expression of PKCθ (kinase-active or inactive) in non-transformed breast epithelial cells (MCF-10A) and assessed effects on epidermal growth factor (EGF)-independent growth, anoikis, and migration. We downregulated expression of PKCθ in TNBC cells, and determined effects on in vitro and in vivo growth and survival. TNBC cells were also treated with a small molecule inhibitor to assess requirement for PKCθ kinase activity in the growth of TNBC cells.ResultsPRKCQ/PKCθ can promote oncogenic phenotypes when expressed in non-transformed MCF-10A mammary epithelial cells; PRKCQ/PKCθ enhances anchorage-independent survival, growth-factor-independent proliferation, and migration. PKCθ expression promotes retinoblastoma (Rb) phosphorylation and cell-cycle progression under growth factor-deprived conditions that typically induce cell-cycle arrest of MCF-10A breast epithelial cells. Proliferation and Rb phosphorylation are dependent on PKCθ-stimulated extracellular signal-related kinase (Erk)/mitogen-activated protein kinase (MAPK) activity. Enhanced Erk/MAPK activity is dependent on the kinase activity of PKCθ, as overexpression of kinase-inactive PKCθ does not stimulate Erk/MAPK or Rb phosphorylation or promote growth-factor-independent proliferation. Downregulation of PRKCQ/PKCθ in TNBC cells enhances anoikis, inhibits growth in 3-D MatrigelTM cultures, and impairs triple-negative tumor xenograft growth. AEB071, an inhibitor of PKCθ kinase activity, also inhibits growth and invasive branching of TNBC cells in 3-D cultures, further supporting a role for PKCθ kinase activity in triple-negative cancer cell growth.ConclusionsEnhanced PRKCQ/PKCθ expression can promote growth-factor-independent growth, anoikis resistance, and migration. PRKCQ critically regulates growth and survival of a subset of TNBC. Inhibition of PKCθ kinase activity may be an attractive therapeutic approach for TNBC, a subtype in need of improved targeted therapies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0749-6) contains supplementary material, which is available to authorized users.