Transformation Of Mammary Cells Research Articles

Abstract 4326: Tissue density can create a carcinogenic microenvironment for normal mammary epithelial cells

Abstract Background Breast cancer is the most diagnosed cancer and the fourth leading cause of cancer related mortality among females. Mammographic density (MD) is defined by the amount of stromal and epithelial tissues present in the breast tissue. Fifty percent of women have high MD and are 4-6 times more likely to develop breast cancer in their lifetime compared to women with low MD. Additionally, mammograms often miss abnormal lesions in high MD breast leading to late-stage diagnosis. The stromal microenvironment is characterized by extracellular matrix (ECM) reorganization and stiffness, and increase in ECM proteins including collagen I and fibronectin, which drives proliferation, tumor cell survival and migration. Expression of fibronectin and collagen are significantly higher in women with high MD compared to women with low MD. However, the mechanisms underlying the initiation and progression of breast cancer associated with MD remains largely unknown. Therefore, understanding the molecular pathways involved in the unique transformation of normal mammary cells to cancer cells in a dense microenvironment is an important step in finding diagnostic tools and therapeutic targets for prevention and treatment of breast cancer. We hypothesize that normal mammary epithelial cells behave like cancer cells in an ECM protein-rich microenvironment by activating pathways associated with tumor growth and survival and contributing to the initiation and progression of breast cancer. Methods We conducted an in vitro study, determining the effects of different concentrations of ECM proteins on the activation of pro-carcinogenic pathways including the MAPK pathway and the PI3 Kinase pathway using Western blotting analysis. This study helps us understand if there is a difference in the expression of ERK1/2 signaling and/or PI3 Kinase signaling in normal mammary cells (hTERT) seeded on culture dish coated with ECM-proteins (collagen and fibronectin), compared to a non-coated control. We also examined morphological changes that can occur in a breast cancer cell line (HCC1806) that are seeded on ECM-rich coating dishes compared to non-coated dishes. Results We observed changes in the morphology of breast cancer cell lines after cells were seeded on increasing concentration of extracellular matrix coatings using light microscopy. We also observed an increase in the expression of PI3 Kinase in normal mammary cell lines compared to control after cells were stressed using hypoxia. Conclusion Collagen and fibronectin-rich microenvironment can induce desmoplastic-like phenotype and behavior for normal mammary cells, which highlights the possible first steps in transformation of normal mammary cells to desmoplastic cells. Given that high MD is one of the major risk factors for breast cancer development, it is critical to decipher the molecular mechanisms associated with the high risk. Citation Format: Shayan Nazari, Pinku Mukherjee. Tissue density can create a carcinogenic microenvironment for normal mammary epithelial cells [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 4326. doi:10.1158/1538-7445.AM2017-4326

Regulation of XIAP Turnover Reveals a Role for USP11 in Promotion of Tumorigenesis

The emerging regulatory role of deubiquitinases (DUBs) has been implicated in various fundamental processes and pathogenesis. To determine the pivotal role that DUBs play in mediating tumorigenesis, we have performed a non-biased screen of 67 human DUBs based on a mammary cell transformation assay. This led to the identification of USP11 as a critical determinant of mammary tumor initiation and progression. Using an approach of protein complex purification coupled with mass spectrometry, we further identified XIAP to be a target for USP11. We demonstrated that, while depletion of XIAP attenuates cell transformation, elevated USP11 significantly promotes the tumor colony formation through stabilization of XIAP. Molecular modeling coupled with mutagenesis analyses further revealed that Leu207 on the BIR2 domain of XIAP facilitates its interaction with USP11. Stabilization of XIAP due to its deubiquitylation by USP11 leads to the inhibition of cell anoikis and apoptosis, which in turn promotes tumorigenesis. Finally, immunohistochemical staining revealed that aberrant accumulation of USP11 correlates with elevated levels of XIAP in breast cancer tissues. We therefore propose that aberrant USP11, via stabilization of XIAP, promotes tumor initiation and progression.

Tissue-specificity of proteoglycans expression in different cancers

Background. Proteoglycans (PGs) are complex glycosylated molecules playing an important role in cell-cell and cell-matrix interactions and signaling. Expression of PGs and their expression pattern change considerably during malignant transformation of mammalian cells and tissues. Objective. The aim of our work was to investigate tissue-specificity of main PGs expression (glypican-1, perlecan, syndecan-1, aggrecan, versican, CSPG4/NG2, brevican, decorin, lumican) in normal cells (fibroblasts and normal epithelial prostate cells PNT2) and in different human cancer cell lines (prostate, breast, lung, brain, kidney). Expression patterns of main PGs were determined in these cells using reverse transcription polymerase chain reaction analysis and immunocytochemical staining. Results. It was shown that fibroblasts actively expressed PGs, and PNT2 cells had lower (5–6-fold) expression levels of a limited set of PG. In different cancer cell lines, overall transcriptional activities of PGs varied up to 10-fold, although their expression patterns had tissue-specific properties (for example, expression of syndecan-1 is more specific for prostate cancer cells, while perlecan is typical for lung cancer cell lines). Conclusions. Along with this, variability of the PG expression patterns in cell lines of the same tissue of origin was shown, suggesting a possible contribution of the variable PGs expression to intratumoural heterogeneity of cancer cells and their potential as perspective biomarker (s) for personalised cancer diagnostics.

Expression of KCNA5 Protein in Human Mammary Epithelial Cell Line Associated with Caveolin-1.

Voltage-gated potassium (Kv) channels are involved in the proliferation and transformation of mammary epithelial cells. They are thought to be related to the development of breast carcinoma, although the exact role they play in this event remains unclear. In this study, we investigated whether the expression and function of Kv channels is associated with Caveolin-1 (Cav-1, a principal component of caveolae) in different cell lines. We found that expression of Cav-1 correlated with the expression of Kv channels in mammary epithelial cells (MCF10A, MCF10A-ST1, and MCF7), and silencing of Cav-1 inhibited the expression of KCNA5 (voltage-gated shaker-related subfamily A, member 5). Immunofluorescence analysis indicated the colocalization of KCNA5 with Cav-1, whereas immunoprecipitation suggested a possible interaction between the two proteins. Overall, our finding indicated that KCNA5 protein may interact with Cav-1, thereby contributing to the proliferation and early transformation of mammary cells.

Developmental signaling pathways regulating mammary stem cells and contributing to the etiology of triple-negative breast cancer.

Cancer has been considered as temporal and spatial aberrations of normal development in tissues. Similarities between mammary embryonic development and cell transformation suggest that the underlying processes required for mammary gland development are also those perturbed during various stages of mammary tumorigenesis and breast cancer (BC) development. The master regulators of embryonic development Cripto-1, Notch/CSL, and Wnt/β-catenin play key roles in modulating mammary gland morphogenesis and cell fate specification in the embryo through fetal mammary stem cells (fMaSC) and in the adult organism particularly within the adult mammary stem cells (aMaSC), which determine mammary progenitor cell lineages that generate the basal/myoepithelial and luminal compartments of the adult mammary gland. Together with recognized transcription factors and embryonic stem cell markers, these embryonic regulatory molecules can be inappropriately augmented during tumorigenesis to support the tumor-initiating cell (TIC)/cancer stem cell (CSC) compartment, and the effects of their deregulation may contribute for the etiology of BC, in particular the most aggressive subtype of BC, triple-negative breast cancer (TNBC). This in depth review will present evidence of the involvement of Cripto-1, Notch/CSL, and Wnt/β-catenin in the normal mammary gland morphogenesis and tumorigenesis, from fMaSC/aMaSC regulation to TIC generation and maintenance in TNBC. Specific therapies for treating TNBC by targeting these embryonic pathways in TICs will be further discussed, providing new opportunities to destroy not only the bulk tumor, but also TICs that initiate and promote the metastatic spread and recurrence of this aggressive subtype of BC.

Abstract P1-06-06: Mammary stem cell modulation of wildtype and Trp53 null stem cells by CAPE (caffeic acid phenethyl ester), a potential therapeutic agent

Abstract CAPE is the major active component of propolis, a widely available, non-toxic, honeybee natural product with anti-inflammatory, antioxidant, and antitumor properties. We have previously shown that CAPE inhibits growth of breast cancer cells and the tumorigenic potential of breast cancer stem cells. We have identified inhibition of histone deacetylase (HDAC) as one mechanism of action, which suggests that it mediates its effects through epigenetic modifications. We postulated that CAPE may be useful in chemoprevention for women at high risk for triple-negative breast cancers since the cell-of-origin hypothesis states that these cancers likely arise from transformation of mammary stem or progenitor cells, whose self-renewal is maintained via epigenetic states. We tested the effect of CAPE on wildtype (WT) and Trp53 null mammary stem cell (MaSC) self-renewal from BALB/c mice cultured as mammospheres (MMS). Primary mammary epithelial cells were cultured as MMS for 7 days, dissociated into single cells, re-cultured in the presence of CAPE for 7 days and passaged in secondary and tertiary passages without CAPE. MMS frequency and differentiation potential was analyzed using immunofluorescence detection of luminal marker, cytokeratin 18, basal marker, cytokeratin 14, and progesterone receptor (PR). Chromatin states were identified using ATAC-seq and open chromatin areas unique to CAPE treated murine MMS were used for pathway analysis performed by Ingenuity Pathway Analysis, Gene Set Enrichment Analysis and confirmed by Integrative Genome Viewer. CAPE treatment resulted in a dose dependent decrease in both WT and p53 null mammosphere forming efficiency that persisted in secondary and tertiary passages, suggesting reduced self-renewal. CAPE treatment also shifted differentiation from predominantly basal K14 to luminal K18-positive in both WT and p53 null MMS and increased PR expression in WT MMS. ATAC-seq of CAPE treated WT MMS showed significant pathway enrichment for p53 signaling, SOX2 signaling, and enrichment of open chromatin for several genes including the SMARCA4 gene, which regulates transcription of genes involved in stem cell renewal. ATAC-seq of CAPE treated Trp53 null MMS showed that genes defining early and late response to estrogen were particularly important. Significant canonical pathways included Aryl hydrocarbon receptor signaling, whose upregulation results in inhibition of self renewal and has been targeted as a potential drug target for estrogen receptor negative breast cancer. The integrin signaling pathway was also highly enriched. These data suggest that CAPE both inhibits MaSC self-renewal and shifts the lineage commitment to a luminal, ER + lineage. ATAC-seq demonstrated genomic effects that are important in differentiation, SC renewal and adhesion. These data suggest that CAPE may have an effect on lineage commitment in support of our chemoprevention strategy to reduce triple-negative breast cancer. Citation Format: Omene C, Patel M, Kannan K, Heguy A, Barcellos-Hoff MH. Mammary stem cell modulation of wildtype and Trp53 null stem cells by CAPE (caffeic acid phenethyl ester), a potential therapeutic agent. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-06-06.

SRSF1-Regulated Alternative Splicing in Breast Cancer

Splicing factor SRSF1 is upregulated in human breast tumors, and its overexpression promotes transformation of mammary cells. Using RNA-seq, we identified SRSF1-regulated alternative splicing (AS) targets in organotypic three-dimensional MCF-10A cell cultures that mimic a context relevant to breast cancer. We identified and validated hundreds of endogenous SRSF1-regulated AS events. De novo discovery of the SRSF1 binding motif reconciled discrepancies in previous motif analyses. Using a Bayesian model, we determined positional effects of SRSF1 binding on cassette exons: binding close to the 5' splice site generally promoted exon inclusion, whereas binding near the 3' splice site promoted either exon skipping or inclusion. Finally, we identified SRSF1-regulated AS events deregulated in human tumors; overexpressing one such isoform, exon-9-included CASC4, increased acinar size and proliferation, and decreased apoptosis, partially recapitulating SRSF1's oncogenic effects. Thus, we uncovered SRSF1 positive and negative regulatory mechanisms, and oncogenic AS events that represent potential targets for therapeutics development.

Abstract 4232: CAPE (caffeic acid phenethyl ester) induces a mammary stem cell lineage restriction to a luminal phenotype via chromatin remodeling

Abstract Propolis, and its active component, CAPE, is a widely available, safe, honeybee natural product with anti-inflammatory, antioxidant, and antitumor properties. We have previously shown that CAPE, inhibits 1) growth of ER+/PR+, ER-/PR- and Her2 + breast cancer cells, 2) the tumorigenic potential of breast cancer stem cells, and 3) mediates its effects through epigenetic modifications via HDAC inhibition, resulting among others, in increased ER in ER- cells. We postulated that CAPE may be useful in chemoprevention for women at high risk for triple-negative breast cancers (TNBC). The cell-of-origin hypothesis states that these cancers arise from transformation of mammary stem cells (SC). We tested the ability of CAPE to inhibit SC self-renewal in murine mammary epithelial cells (MEC) and a human breast epithelial cell line (MCF10A). MEC isolated from BALB/c mice were cultured as mammospheres (MMS) for 7 days in ULA 96 well plates using media containing 5% FBS and 5% Matrigel. MMS were dissociated into single cells, recultured in the presence of CAPE for 7 days and passaged in secondary and tertiary passages in media alone. Alternatively, MCF10A transfected with a Let7c-miRNA reporter were sorted for Let7c-negative cells, and similarly cultured with CAPE. Murine MMS were analyzed for luminal marker, K18, basal marker K14, or progesterone receptor (PR) using immunofluorescence. Open chromatin states were identified using ATAC-seq and peaks were independently called using PeakDeck. Open chromatin areas unique to CAPE treated murine MMS were used for pathway analysis performed by Ingenuity Pathway Analysis and confirmed by Integrative Genome Viewer. CAPE treatment resulted in a dose dependent decrease in mammosphere forming efficiency that persisted in secondary and tertiary passages, indicating reduced self-renewal. CAPE shifted the cells within murine MMS from predominantly K14 to K18-positive and increased PR expression. Interestingly, ATAC-seq showed enrichment of open chromatin of the SMARCA4 gene in the exonic region. SMARCA4 is a chromatin remodeling gene that is involved in SWI/SNF complex and alters the positioning of the nucleosome, it is thought to regulate transcription of certain genes by altering the chromatin structure around those genes. In addition, SMARCA4 can bind BRCA1, and regulate the expression of the tumorigenic breast cancer SC marker, CD44. These data indicate that CAPE both inhibited mammary SC self-renewal and shifted the lineage commitment to a luminal lineage. ATAC-seq demonstrated effects at the chromatin level that may regulate the SMARCA4 gene, which controls the transcription of many genes involved in stem cell renewal, pluripotency, and embryonic development and is differentially expressed in the luminal phenotype of human MEC. Thus, CAPE may have an effect on lineage commitment in agreement with our chemoprevention strategy to reduce TNBC breast cancer development. Citation Format: Coral O. Omene, Manan Patel, Kasthuri Kannan, Adriana Heguy, Mary Helen Barcellos-Hoff. CAPE (caffeic acid phenethyl ester) induces a mammary stem cell lineage restriction to a luminal phenotype via chromatin remodeling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4232. doi:10.1158/1538-7445.AM2015-4232

Dynamics of MBD2 deposition across methylated DNA regions during malignant transformation of human mammary epithelial cells.

DNA methylation is thought to induce transcriptional silencing through the combination of two mechanisms: the repulsion of transcriptional activators unable to bind their target sites when methylated, and the recruitment of transcriptional repressors with specific affinity for methylated DNA. The Methyl CpG Binding Domain proteins MeCP2, MBD1 and MBD2 belong to the latter category. Here, we present MBD2 ChIPseq data obtained from the endogenous MBD2 in an isogenic cellular model of oncogenic transformation of human mammary cells. In immortalized (HMEC-hTERT) or transformed (HMLER) cells, MBD2 was found in a large proportion of methylated regions and associated with transcriptional silencing. A redistribution of MBD2 on methylated DNA occurred during oncogenic transformation, frequently independently of local DNA methylation changes. Genes downregulated during HMEC-hTERT transformation preferentially gained MBD2 on their promoter. Furthermore, depletion of MBD2 induced an upregulation of MBD2-bound genes methylated at their promoter regions, in HMLER cells. Among the 3,160 genes downregulated in transformed cells, 380 genes were methylated at their promoter regions in both cell lines, specifically associated by MBD2 in HMLER cells, and upregulated upon MBD2 depletion in HMLER. The transcriptional MBD2-dependent downregulation occurring during oncogenic transformation was also observed in two additional models of mammary cell transformation. Thus, the dynamics of MBD2 deposition across methylated DNA regions was associated with the oncogenic transformation of human mammary cells.

Abstract B27: SERPINE1 expression is required for HDACi-induced proliferative arrest in ras-transformed epithelial cells

Abstract Malignant transformation of mammalian cells with ras family oncogenes results in dramatic changes in cellular architecture and growth traits. The generation of flat revertants of v-K-ras-transformed epithelial cells by exposure to the histone deacetylase inhibitor sodium butyrate (NaB) was found to be dependent on transcriptional activation of the SERPINE1 gene (encoding the type-1 inhibitor of urokinase and tissue-type plasminogen activators; PAI-1). NaB-initiated SERPINE1 expression preceded induced cell spreading and G1 arrest. To assess the relevance of SERPINE1 induction to proliferative blockade in this cell system more critically, several complementary approaches were used. The addition of a stable, long half-life, recombinant SERPINE1 mutant to SERPINE1-deficient v-K-ras-/c-Ha-ras-transformants or to SERPINE1 functionally null, NaB-resistant, 4HH cells (engineered by antisense knockdown of SERPINE1 mRNA transcripts) resulted in marked cytostasis in the absence of NaB. Transfection of ras-transformed cells with the Rc/CMVSERPINE1 expression vector or infection with an adenoviral SERPINE1 construct, moreover, significantly elevated constitutive SERPINE1 synthesis (10- to 20-fold) with a concomitant reduction in proliferative rate. These data suggest that high-level SERPINE1 expression suppresses growth of chronic ras-oncogene transformed cells and is likely a major cytostatic effector of NaB exposure. Supported by NIH grant GM057242. Note: This abstract was not presented at the conference. Citation Format: Paul J. Higgins. SERPINE1 expression is required for HDACi-induced proliferative arrest in ras-transformed epithelial cells. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B27. doi: 10.1158/1557-3125.RASONC14-B27

Abstract 1579: Induction of cytotoxicity by soluble chromium (VI) compounds in cultured C3H/10T1/2 Cl 8 mouse embryo cells effects of ascorbate and dehydroascorbate

Abstract Hexavalent chromium [Cr(VI)]-containing compounds are human carcinogens. They cause cancers in the respiratory system when inhaled, and stomach/other internal cancers when ingested. Soluble and insoluble hexavalent chromium [Cr(VI)] compounds induced base substitution, deletion, addition, and frameshift mutations. Cr(VI) compounds also induce DNA-DNA cross links and DNA-protein cross-links in mammalian cells. We examined the ability of the soluble chromium compounds, sodium chromate (Na2CrO4), calcium chromate (CaCrO4) and potassium chromate (K2CrO4) to induce cytotoxicity and morphological transformation in C3H/10T½ Cl 8 (10T1/2) mouse embryo cells. We tested the hypothesis that the intracellular reductants, ascorbate and dehydroascorbate, can reduce Cr(VI) to Cr(V), Cr(IV), and Cr(III) intracellularly, making it a strong cytotoxin in mammalian cells. Ascorbate is present in serum at concentrations in the mM range under physiological conditions in humans, but is only present in the μM range in mouse embryo cells grown in BME cell culture medium plus 10% fetal calf serum. We hypothesized the relatively weak responses for induction of morphological transformation of mammalian cells by Cr(VI) compounds in culture (dose-dependent but weak induction of foci by lead chromate, and no induction of foci by calcium chromate, potassium chromate, and sodium chromate) is due to the small amounts of ascorbate in cultures of mammalian cells that are insufficient to reduce Cr(VI) to Cr(V), Cr(IV), and Cr(III). Therefore, we investigated the cytotoxic effects of ascorbate on 10T½ mouse embryo cells, and the effects of the highest non-cytotoxic concentrations of ascorbate on Cr(VI)-induced cytotoxicity in 10T½ cells, using reduction in plating efficiency as our cytotoxicity assay. Cell survival data showed that ascorbate itself exerted significant cytotoxic effects at concentrations of 0.00625 mM and higher on 10T½ mouse embryo cells. Furthermore, when 10T½ cells were treated with both Cr(VI) and ascorbate, ascorbate played dual roles. It served as a pro-oxidant (enhancer of the cytotoxicity of chromate) at concentrations up to 0.1 mM, and as an anti-oxidant (reducer of the cytotoxicity of chromate) at concentrations of 0.25 mM and higher. This information is important for our ongoing and future experiments, where we designed a protocol to incorporate ascorbate into our assays assessing the cytotoxicity and cell transforming activity of Cr(VI) compounds. We project that at concentrations of 0.1 mM and lower, ascorbate will enhance the cell transforming activity of Cr(VI) compounds. Supported by undergraduate fellowships from the Provost's Office at the University of Southern California (USC) (P. I., JRL), by funding from the M. S. Program in Molecular Microbiology and Immunology to JRL, by discretionary funding to JRL, and by prior grant ES03341 from NIEHS/NIH (P. I., JRL). Citation Format: Sophia A. Shahin, William Liao, Laureen Tran, Qasim A. Akinwumi, Farn-shuan Tseng, Alyssa Mathew-Joseph, Joseph R. Landolph. Induction of cytotoxicity by soluble chromium (VI) compounds in cultured C3H/10T1/2 Cl 8 mouse embryo cells effects of ascorbate and dehydroascorbate. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1579. doi:10.1158/1538-7445.AM2014-1579

Abstract 1306: Synergistic function of a novel cell cycle regulator, Ecdysoneless with oncogenic Ras in the regulation of cell cycle and transformation

Abstract We have previously identified the mammalian ortholog of Drosophila ecdysoneless (Ecd) protein as a novel and essential regulator of Rb-E2F-dependent cell cycle progression. Consistent with role of Ecd in cell cycle, our recent studies show Ecd is overexpressed in breast cancer cell lines as well as in ductal carcinoma in situ and infiltrating ductal carcinomas of the breast. To explore the mechanism of Ecd overexpression and its correlation with oncogenesis, we overexpressed either Ecd alone, HRas-61L alone or both genes together in hTERT-immortalized human mammary epithelial cells (hMECs). These transfectants were then examined for their oncogenic properties. We observed while vector infected cells do not exhibit anchorage independence, all three transfectants showed increase in anchorage independent proliferation, particularly Ecd+Ras showed a significant increase in anchorage independence in comparison with either Ecd or Ras. Similarly, other oncogenic traits such as proliferation on matrigel, invasion and migration were dramatically increased when both genes were expressed in comparison with individual genes. Further analysis showed Ecd+Ras-expressing hMECs were unable to synchronize completely after growth factor deprivation and showed rapid progression into cell cycle, demonstrating synergy in altered cell cycle pathways in these cells. Most significantly, Ecd+Ras expressing hMECs were able to form tumors when implanted into mammary fat pads of NOD-SCID mice, whereas no tumors were observed with Ecd or Ras alone. These results demonstrate complete transformation of hMECs by overexpression of Ecd together with mutant Ras. Considering the known oncogenic role of Ras in human cancer and the known role of Ecd in cell cycle, these data are highly significant and present a novel synergistic pathway for mammary cell transformation. Current studies are directed towards defining the mechanism of synergy between Ecd and Ras in cellular transformation. Citation Format: Aditya Bele, Sameer Mirza, Riyaz Mir, Shakur Mohibi, Hamid Band, Vimla Band. Synergistic function of a novel cell cycle regulator, Ecdysoneless with oncogenic Ras in the regulation of cell cycle and transformation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1306. doi:10.1158/1538-7445.AM2014-1306

Cas proteins: dodgy scaffolding in breast cancer.

The members of the Cas protein family (p130Cas/BCAR1, Nedd9/HEF1, EFS and CASS4) are scaffold proteins required for the assembly of signal transduction complexes in response to several stimuli, such as growth factors, hormones and extracellular matrix components. Given their ability to integrate and coordinate multiple signalling events, Cas proteins have emerged as crucial players in the control of mammary cell proliferation, survival and differentiation. More importantly, it has been found that alterations of their expression levels result in aberrant signalling cascades, which promote initiation and progression of breast cancer. Based on the increasing data from in vitro, mouse model and clinical studies, in this review we will focus on two Cas proteins, p130Cas/BCAR1 and Nedd9, and their coupled signalling pathways, to examine their role in mammary cell transformation and in the acquirement of invasiveness and drug resistance of breast cancer cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0443-5) contains supplementary material, which is available to authorized users.

The role of miR-200a in mammalian epithelial cell transformation.

Cancer is a multistep disease that begins with malignant cell transformation and frequently culminates in metastasis. MicroRNAs (miRNAs) are small regulatory 21-25 nt RNA molecules and are frequently deregulated in cancer. miR-200a is a member of the miR-200 family, which are known inhibitors of the epithelial-to-mesenchymal transition. As such, the tumor-suppressive role of miR-200a in oncogenesis has been well documented; however, recent studies have found a proliferative role for this miRNA as well as a prometastatic role in the later steps of cancer progression. Little is known about the role of this miRNA in the early stages of cancer, namely, malignant cell transformation. Here, we show that miR-200a alone transforms an immortalized rat epithelial cell line, and miR-200a cooperates with Ras to enhance malignant transformation of an immortalized human epithelial cell line. Furthermore, miR-200a induces cell transformation and tumorigenesis in immunocompromised mice by cooperating with a Ras mutant that activates only the RalGEF effector pathway, but not Ras mutants activating PI3K or Raf effector pathways. This transformative ability is in accordance with miR-200a targeting Fog2 and p53 to activate Akt and directly repress p53 protein levels, respectively. These results demonstrate an oncogenic role for miR-200a and provide a specific cellular context where miR-200a acts as an oncomiR rather than a tumor suppressor by cooperating with an oncogene in malignant cell transformation.

How a replication origin and matrix attachment region accelerate gene amplification under replication stress in mammalian cells.

The gene amplification plays a critical role in the malignant transformation of mammalian cells. The most widespread method for amplifying a target gene in cell culture is the use of methotrexate (Mtx) treatment to amplify dihydrofolate reductase (Dhfr). Whereas, we found that a plasmid bearing both a mammalian origin of replication (initiation region; IR) and a matrix attachment region (MAR) was spontaneously amplified in mammalian cells. In this study, we attempted to uncover the underlying mechanism by which the IR/MAR sequence might accelerate Mtx induced Dhfr amplification. The plasmid containing the IR/MAR was extrachromosomally amplified, and then integrated at multiple chromosomal locations within individual cells, increasing the likelihood that the plasmid might be inserted into a chromosomal environment that permits high expression and further amplification. Efficient amplification of this plasmid alleviated the genotoxicity of Mtx. Clone-based cytogenetic and sequence analysis revealed that the plasmid was amplified in a chromosomal context by breakage-fusion-bridge cycles operating either at the plasmid repeat or at the flanking fragile site activated by Mtx. This mechanism explains how a circular molecule bearing IR/MAR sequences of chromosomal origin might be amplified under replication stress, and also provides insight into gene amplification in human cancer.

Mammalian cell-transforming potential of traffic-linked ultrafine particulate matter PM0.056 in urban roadside atmosphere.

We examined the clastogenic and cell-transforming potential of ultrafine particulate matter fraction PM0.056 of urban ambient aerosol using mammalian cells. PM1.0, PM0.56 and PM0.056 fractions were sampled from roadside atmosphere of an urban area using the cascade impactor MOUDI-NR-110. The potential to induce cytotoxicity, DNA damage and micronuclei formation was examined at the test concentrations of 3, 6, 12.5, 25, 50 and 100 μg/ml using the 3-4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, the plasmid relaxation assay and the C3H10T1/2 (10T1/2) cells. The cell-transforming potential was investigated in vitro using 10T1/2 cell transformation assay and the soft agar assay. PM1, PM0.56 and PM0.056 fractions were found to be toxic in dose-dependent manner. These induced cytotoxicity at five test concentrations, the ultrafine particle fraction PM0.056 showed greater cytotoxic potential. PM0.056 induced micronucleus formation in 10T1/2 cells. The effect was statistically significant. The DNA-damaging potential was measured in a plasmid relaxation assay. Both fine and ultrafine particle fraction PM0.56 and PM0.056 displayed greater effect as compared to larger PM1 fraction. DNA damage was found to be dependent on particulate matter intrinsic pro-oxidant chemicals. The ability of the ultrafine particle fraction PM0.056 to induce morphological cell transformation was demonstrated by significant and dose-dependent increases in type III focus formation by morphologically transformed cells in culture flasks and their clonal expansion in soft agar. It is concluded that the traffic-linked ultrafine particle fraction PM0.056 in the atmosphere by the roadside of an urban area is clastogenic and able to induce morphological transformation of mammalian cells.

What is the future potential of the PI3K pathway in colorectal cancer treatment?

Systems Biology & Personalised Medicine Division, Walter & Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia Faculty of Medicine, Dentistry & Health Sciences, Department of Medical Biology, University of Melbourne, Parkville, Victoria, Australia Department of Medical Oncology, Royal Melbourne Hospital, Parkville & Western Hospital, Footscray, Victoria, Australia *Author for correspondence: oliver.sieber@ludwig.edu.au Therapeutic options for treating patients with metastatic colorectal cancer (CRC) have increased markedly over the past decade. Recent improvements in overall survival rates from 10 to 24 months have been achieved through the introduction of molecularly targeted agents to complement traditional cytotoxics, including agents directed against the EGF receptor (EGFR) pathway (cetuximab and panitumumab) and angiogenesis (bevacizumab, aflibercept and regorafenib). This progress has spurred intense efforts to develop further compounds that target key molecular pathways driving carcinogenesis. One major focus has been on the inhibition of oncogenic PI3K signaling, with diverse inhibitors currently in Phase I/II clinical trials. While achieving clear responses in some cancers, activity in CRC has been modest, with disease stabilization observed in approximately 10% of patients. Here, we discuss the potential opportunities of targeting the PI3K pathway in treating patients with metastatic CRC. PI3K/AKT signaling is typically initiated via growth factors (e.g., EGF) or insulin, resulting in activation of receptor tyrosine kinases or G-protein coupled receptors. Activated receptor tyrosine kinases/G-protein coupled receptors recruit and activate class IA PI3K at the cell membrane, enabling PI3K to convert PIP2 to PIP3. PIP3 recruits the serene–threonine protein kinase AKT, which is rendered fully active through phosphorylation by PDK1 and mTORC2. Phosphorylated AKT transduces the signal to a range of downstream substrates (e.g., NF-κB, TSC1/2 complex, mTORC1, S6K, 4EBP1, BAD, GSK3β and MDM2) affecting cell proliferation, growth, survival, apoptosis, protein synthesis and glucose metabolism [1]. PI3K signaling is negatively regulated by the PTEN phosphatase, which removes the 3-phosphate from PIP3. In addition, PI3K can be stimulated by GTP-bound RAS, a crosstalk important for RAS mutation-induced transformation of mammalian cells. Michelle Palmieri1,2, Jayesh Desai1,3 & Oliver Sieber*,1

N-nitroso-N-ethylurea activates DNA damage surveillance pathways and induces transformation in mammalian cells.

BackgroundThe DNA damage checkpoint signalling cascade sense damaged DNA and coordinates cell cycle arrest, DNA repair, and/or apoptosis. However, it is still not well understood how the signalling system differentiates between different kinds of DNA damage. N-nitroso-N-ethylurea (NEU), a DNA ethylating agent induces both transversions and transition mutations.MethodsImmunoblot and comet assays were performed to detect DNA breaks and activation of the canonical checkpoint signalling kinases following NEU damage upto 2 hours. To investigate whether mismatch repair played a role in checkpoint activation, knock-down studies were performed while flow cytometry analysis was done to understand whether the activation of the checkpoint kinases was cell cycle phase specific. Finally, breast epithelial cells were grown as 3-dimensional spheroid cultures to study whether NEU can induce upregulation of vimentin as well as disrupt cell polarity of the breast acini, thus causing transformation of epithelial cells in culture.ResultsWe report a novel finding that NEU causes activation of major checkpoint signalling kinases, Chk1 and Chk2. This activation is temporally controlled with Chk2 activation preceding Chk1 phosphorylation, and absence of cross talk between the two parallel signalling pathways, ATM and ATR. Damage caused by NEU leads to the temporal formation of both double strand and single strand breaks. Activation of checkpoints following NEU damage is cell cycle phase dependent wherein Chk2 is primarily activated during G2-M phase whilst in S phase, there is immediate Chk1 phosphorylation and delayed Chk2 response. Surprisingly, the mismatch repair system does not play a role in checkpoint activation, at doses and duration of NEU used in the experiments. Interestingly, NEU caused disruption of the well-formed polarised spheroid archithecture and upregulation of vimentin in three-dimensional breast acini cultures of non-malignant breast epithelial cells upon NEU treatment indicating NEU to have the potential to cause early transformation in the cells.ConclusionNEU causes damage in mammalian cells in the form of double strand and single strand breaks that temporally activate the major checkpoint signalling kinases without the occurrence of cross-talk between the pathways. NEU also appear to cause transformation in three-dimensional spheroid cultures.

PKA signaling drives mammary tumorigenesis through Src

Protein kinase A (PKA) hyperactivation causes hereditary endocrine neoplasias; however, its role in sporadic epithelial cancers is unknown. Here, we show that heightened PKA activity in the mammary epithelium generates tumors. Mammary-restricted biallelic ablation of Prkar1a, which encodes for the critical type-I PKA regulatory subunit, induced spontaneous breast tumors characterized by enhanced type-II PKA activity. Downstream of this, Src phosphorylation occurs at residues serine-17 and tyrosine-416 and mammary cell transformation is driven through a mechanism involving Src signaling. The phenotypic consequences of these alterations consisted of increased cell proliferation and, accordingly, expansion of both luminal and basal epithelial cell populations. In human breast cancer, low PRKAR1A/high SRC expression defines basal-like and HER2 breast tumors associated with poor clinical outcome. Together, the results of this study define a novel molecular mechanism altered in breast carcinogenesis and highlight the potential strategy of inhibiting SRC signaling in treating this cancer subtype in humans.

Regulation of Ras localization and cell transformation by evolutionarily conserved palmitoyltransferases.

Ras can act on the plasma membrane (PM) to mediate extracellular signaling and tumorigenesis. To identify key components controlling Ras PM localization, we performed an unbiased screen to seek Schizosaccharomyces pombe mutants with reduced PM Ras. Five mutants were found with mutations affecting the same gene, S. pombe erf2 (sp-erf2), encoding sp-Erf2, a palmitoyltransferase, with various activities. sp-Erf2 localizes to the trans-Golgi compartment, a process which is mediated by its third transmembrane domain and the Erf4 cofactor. In fission yeast, the human ortholog zDHHC9 rescues the phenotypes of sp-erf2 null cells. In contrast, expressing zDHHC14, another sp-Erf2-like human protein, did not rescue Ras1 mislocalization in these cells. Importantly, ZDHHC9 is widely overexpressed in cancers. Overexpressing ZDHHC9 promotes, while repressing it diminishes, Ras PM localization and transformation of mammalian cells. These data strongly demonstrate that sp-Erf2/zDHHC9 palmitoylates Ras proteins in a highly selective manner in the trans-Golgi compartment to facilitate PM targeting via the trans-Golgi network, a role that is most certainly critical for Ras-driven tumorigenesis.