Regulates Cancer Stem Cell Properties Research Articles

Identification of the epigenetic mechanism for colorectal cancer stem cell regulation through the comprehensive microRNA expression profiling of human colorectal cancer tissues.

42 Background: MicroRNAs (miRNAs) are key regulators of cancer stem cell (CSC) functions, including self-renewal and differentiation. However, little is known about miRNAs that regulate such properties in human colorectal cancer. Methods: We compared the expression levels of 754 miRNAs between paired samples of EpCAM+/CD44+ cancer cells (enriched in CSCs) and EpCAM+/CD44neg cancer cells (non-tumorigenic cancer cells (NTCs)) sorted in parallel from human primary colorectal cancers by multiplex semi-quantitative PCR. Results: Comparison of the expression levels of miRNAs in the CSCs and NTCs resulted in the identification of 10 miRNAs upregulated (miR-221, miR-218, miR-500 and miR-195) or downregulated (miR-185, miR-19a, miR-337, miR-10a, miR-21 and miR-24) in CSCs compared to NTCs. Among them, miR-221 was most highly expressed in CSCs; and its expression level was very low in NTCs and normal colon epithelial cells (n=6, p<0.05). Kaplan-Myer estimates and univariate and multivariate analyses showed that higher miR-221 expression was an independent prognosis factor for poorer outcome. Constitutive overexpression of miR-221 enhanced organoid-forming capacity of both conventional colorectal carcinoma cell lines and patient-derived xenografts (PDX) in vitro. Importantly, constitutive downregulation of miR-221 suppressed organoid-forming capacity in vitro and substantially reduced the tumorigenic capacity of CSC populations from PDX lines in vivo. miR-221 directly targeted Quaking (QKI) 5, the most abundant splicing isoform of the human QKI gene, and suppressed its protein level. Knockdown of miR-221 suppressed the clonogenicity of colorectal CSCs in vitro in a QKI-expression dependent manner and ability to form tumors in vivo. Conclusions: Our study reveals a mechanistic link between miR-221 and QKI and highlights their key role in regulating CSC properties in human colorectal cancer and proposes that miR-221 will be a promising marker and a specific therapeutic target for human colorectal CSCs.

E3 ubiquitin ligases in cancer stem cells: key regulators of cancer hallmarks and novel therapeutic opportunities.

Human malignancies are composed of heterogeneous subpopulations of cancer cells with phenotypic and functional diversity. Among them, a unique subset of cancer stem cells (CSCs) has both the capacity for self-renewal and the potential to differentiate and contribute to multiple tumor properties. As such, CSCs are promising cellular targets for effective cancer therapy. At the molecular level, hyper-activation of multiple stemness regulatory signaling pathways and downstream transcription factors play critical roles in controlling CSCs establishment and maintenance. To regulate CSC properties, these stemness pathways are controlled by post-translational modifications including, but not limited to phosphorylation, acetylation, methylation, and ubiquitination. In this review, we focus on E3 ubiquitin ligases and their roles and mechanisms in regulating essential hallmarks of CSCs, such as self-renewal, invasion and metastasis, metabolic reprogramming, immune evasion, and therapeutic resistance. Moreover, we discuss emerging therapeutic approaches to eliminate CSCs through targeting E3 ubiquitin ligases by chemical inhibitors and proteolysis-targeting chimera (PROTACs) which are currently under development at the discovery, preclinical, and clinical stages. Several outstanding issues such as roles for E3 ubiquitin ligases in heterogeneity and phenotypical/functional evolution of CSCs remain to be studied under pathologically and clinically relevant conditions. With the rapid application of functional genomic and proteomic approaches at single cell, spatiotemporal, and even single molecule levels, we anticipate that more specific and precise functions of E3 ubiquitin ligases will be delineated in dictating CSC properties. Rational design and proper translation of these mechanistic understandings may lead to novel therapeutic modalities for cancer procession medicine.

234P Epithelial-mesenchymal transition and cancer stem cells: Missing link in oral squamous cell carcinoma

Cancer stem cells (CSCs) are a heterogeneous population of cancer cells with characteristics similar to normal stem cells, including the ability for self-renewal and differentiation. CSCs can differentiate into tumor-supporting cells potentially enabling metastasis, relapse, and chemoresistance. Complex networks involving several transcription factors, such as Nanog, Oct4, SOX2, and various miRNAs, have been identified to regulate CSC properties. The EMT is a process in which epithelial cells change their morphology, lose their polarity and acquire the migratory properties of mesenchymal cells.

Abstract 5826: Autophagy regulates cancer stem cell properties in triple negative breast cancer via miR-181a-mediated regulation of ATG5/ATG2B

Abstract Autophagy has a dual role in the maintenance of cancer stem cells (CSCs), but the precise relationship between autophagy and cancer stemness requires further investigation. In this study, it was found that luminal and triple-negative breast cancer require distinct therapeutic approaches because of their different expressions of autophagy flux. We identified that autophagy flux was inhibited in triple-negative breast cancer (TNBC) CSCs. Moreover, miRNA-181a (miR-181a) is upregulated both in TNBC CSCs and patients. ATG5 and ATG2B participate in the early formation of autophagosomes and were revealed as targets of miR-181a. Inhibition of miR-181a expression led to attenuation of TNBC cancer stemness and an increase in autophagy flux. Furthermore, treatment with curcumin led to attenuation of cancer stemness in TNBC CSCs; the expression of ATG5 and ATG2B was enhanced and there was an increase of autophagy flux. These results indicated that ATG5 and ATG2B are involved in the suppression of cancer stemness in TNBC. In summary, autophagy inhibits cancer stemness through the miR-181a-regulated mechanism in TNBC. Promoting tumor-suppressive autophagy using curcumin may be a potential method for the treatment of TNBC. Citation Format: Jong Hoon Park, Jee Won Park, Yesol Kim, Jaehee Jun, Yejin Ahn. Autophagy regulates cancer stem cell properties in triple negative breast cancer via miR-181a-mediated regulation of ATG5/ATG2B [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 5826.

DNMT1-mediated methylation of BEX1 regulates stemness and tumorigenicity in liver cancer

Hepatoblastoma (HB) and hepatocellular carcinoma (HCC) both exhibit notable cancer stem cell (CSC) features. Moreover, the development of both diseases is closely associated with the presence of CSCs. We investigated the role of brain-expressed X-linked protein 1 (BEX1) in regulating the CSC properties of HB and a subtype of HCC with high CSC features (CSC-HCC). Stemness scores were analyzed in 5 murine HCC models. A subpopulation of BEX1-positive cells and BEX1-negative cells were sorted from HCC cell lines, and subjected to transcriptome analysis. The expression and function of BEX1 was examined via western blotting, sphere formation assays, and xenograft tumor models. We identified BEX1 as a novel CSC marker that was required for the self-renewal of liver CSCs. Furthermore, zebularine, a potent DNMT1 inhibitor, can induce the reactivation of BEX1 by removing epigenetic inhibition. Notably, BEX1 was highly expressed in patients with HB and CSC-HCC, but not in patients with non-CSC HCC. Moreover, DNMT1-mediated methylation of the BEX1 promoter resulted in differential BEX1 expression patterns in patients with HB, CSC-HCC, and non-CSC-HCC. Mechanistically, BEX1 interacted with RUNX3 to block its inhibition of β-catenin transcription, which led to the activation of Wnt/β-catenin signaling, and stemness maintenance in both HB and CSC-HCC. In contrast, downregulated BEX1 expression released RUNX3 and inhibited the activation of Wnt/β-catenin signaling in non-CSC-HCC. BEX1, under the regulation of DNMT1, is necessary for the self-renewal and maintenance of liver CSCs through activation of Wnt/β-catenin signaling, rendering BEX1 a potentially valuable therapeutic target in both HB and CSC-HCC. Cancer stem cells (CSCs) contribute to a high rate of cancer recurrence, as well as resistance to conventional therapies. However, the regulatory mechanisms underlying their self-renewal remains elusive. Herein, we have reported that BEX1 plays a key role in regulating CSC properties in different types of liver cancer. Targeting BEX1-mediated Wnt/β-catenin signaling may help to address the high rate of recurrence, and heterogeneity of liver cancer.

Abnormal Glycosylation of Cancer Stem Cells and Targeting Strategies.

Cancer stem cell (CSCs) are deemed as one of the main reasons of tumor relapse due to their resistance to standard therapies. Numerous intracellular signaling pathways along with extracellular features are crucial in regulating CSCs properties, such as heterogeneity, plasticity and differentiation. Aberrant glycosylation of these cellular signaling pathways and markers of CSCs have been directly correlated with maintaining survival, self-renewal and extravasation properties. In this review, we highlight the importance of glycosylation in promoting stemness character of CSCs, and present strategies for targeting abnormal glycosylation to eliminate the resistant CSC population.

Hexosamine Signaling Regulates Cancer Stem Cell Properties: Significance of Hyaluronan Production and Protein <i>O</i>-GlcNAcylation

Hexosamine Signaling Regulates Cancer Stem Cell Properties: Significance of Hyaluronan Production and Protein <i>O</i>-GlcNAcylation

Hexosamine Signaling Regulates Cancer Stem Cell Properties: Significance of Hyaluronan Production and Protein <i>O</i>-GlcNAcylation

Hyaluronan (HA) is a major glycosaminoglycan in the extracellular matrix and is also seen in the tumor microenvironment. HA-rich matrix is widely observed in tumor tissues and is strongly related to the malignancy potential. HA production was closely associated with the regulation of cancer stem cells (CSCs). CSCs are a stem cell-like subpopulation of cancer cells and are considered to be responsible for tumor initiation, growth, and recurrence. Recent findings suggested that the regulation of CSC properties strongly depends on cancer metabolism. HA production markedly induces the reprogramming of glucose metabolism, including the hexosamine biosynthetic pathway (HBP). The end product of HBP is a nucleotide sugar UDP-N-acetylglucosamine (UDP-GlcNAc) which is utilized as a substrate for HA and glycosaminoglycans synthesis as well as for O-linked N-acetylglucosamine (O-GlcNAc) modification of proteins. Protein O-GlcNAcylation is another essential factor for the regulation of CSC properties. In this minireview, I outline the significance of HA production and O-GlcNAcylation in CSC regulation.

Autophagy Regulates Cancer Stem Cell Properties in Triple Negative Breast Cancer Via miR-181a-Mediated Regulation of ATG5/ATG2B

Background: Cancer stemness, miRNA, and autophagy flux are known to contribute to the maintenance of cancers; however, determination of the precise interactions among autophagy, miRNAs, and cancer stemness requires further investigation. Methods: Western blot, immunocytochemistry, immunofluorescence staining, quantitative real-time PCR were performed to detect gene expression. Tumorsphere formation assay, Aldefluor assay, limiting dilution assay were carried out to measure cancer stemness. Acridine orange and Cyto-ID® staining were used to detect autophagy vacuoles. Findings: Autophagy flux was inhibited in triple-negative breast cancer (TNBC) cancer stem cells (CSCs). Moreover, miRNA-181a (miR-181a) is upregulated both in TNBC CSCs and patients. ATG5 and ATG2B participate in the early formation of autophagosomes and were revealed as targets of miR-181a. Inhibition of miR-181a expression led to attenuation of cancer stemness and an increase in autophagy flux. Furthermore, treatment with curcumin led to attenuation of cancer stemness in TNBC CSCs; the expression of ATG5 and ATG2B was enhanced and there was an increase of autophagy flux. Interpretation: It could be suggested that luminal and triple-negative breast cancer require distinct therapeutic approaches because of their different expressions of autophagy flux. These results indicated that ATG5 and ATG2B are involved in the suppression of cancer stemness in TNBC. Autophagy inhibits cancer stemness through the miR-181a-regulated mechanism in TNBC. Promoting tumor-suppressive autophagy using curcumin may be a potential method for the treatment of TNBC. Funding: This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) (2019R1A2B5B03069738, NRF- 2016R1A5A1011974). Declaration of Interest: All the authors declared no competing interests. Ethical Approval: This study was approved by the 235 Institutional Review Board of Seoul National University Hospital (IRB number: 1704-236 019-843). A breast cancer tissue array (BC081120f, US Biomax Inc, USA).

The Cellular Prion Protein: A Promising Therapeutic Target for Cancer.

Studies on the cellular prion protein (PrPC) have been actively conducted because misfolded PrPC is known to cause transmissible spongiform encephalopathies or prion disease. PrPC is a glycophosphatidylinositol-anchored cell surface glycoprotein that has been reported to affect several cellular functions such as stress protection, cellular differentiation, mitochondrial homeostasis, circadian rhythm, myelin homeostasis, and immune modulation. Recently, it has also been reported that PrPC mediates tumor progression by enhancing the proliferation, metastasis, and drug resistance of cancer cells. In addition, PrPC regulates cancer stem cell properties by interacting with cancer stem cell marker proteins. In this review, we summarize how PrPC promotes tumor progression in terms of proliferation, metastasis, drug resistance, and cancer stem cell properties. In addition, we discuss strategies to treat tumors by modulating the function and expression of PrPC via the regulation of HSPA1L/HIF-1α expression and using an anti-prion antibody.

Cancer Cell CD44 Mediates Macrophage/Monocyte-Driven Regulation of Head and Neck Cancer Stem Cells.

Tumor-associated macrophages (TAM) in the tumor microenvironment (TME) cooperate with cancer stem cells (CSC) to maintain stemness. We recently identified cluster of differentiation 44 (CD44) as a surface marker defining head and neck squamous cell carcinoma (HNSCC) CSC. PI3K-4EBP1-SOX2 activation and signaling regulate CSC properties, yet the upstream molecular control of this pathway and the mechanisms underlying cross-talk between TAM and CSC in HNSCC remain largely unknown. Because CD44 is a molecular mediator in the TME, we propose here that TAM-influenced CD44 signaling could mediate stemness via the PI3K-4EBP1-SOX2 pathway, possibly by modulating availability of hyaluronic acid (HA), the main CD44 ligand. HNSCC IHC was used to identify TAM/CSC relationships, and in vitro coculture spheroid models and in vivo mouse models were used to identify the influence of TAMs on CSC function via CD44. Patient HNSCC-derived TAMs were positively and negatively associated with CSC marker expression at noninvasive and invasive edge regions, respectively. TAMs increased availability of HA and increased cancer cell invasion. HA binding to CD44 increased PI3K-4EBP1-SOX2 signaling and the CSC fraction, whereas CD44-VCAM-1 binding promoted invasive signaling by ezrin/PI3K. In vivo, targeting CD44 decreased PI3K-4EBP1-SOX2 signaling, tumor growth, and CSC. TAM depletion in syngeneic and humanized mouse models also diminished growth and CSC numbers. Finally, a CD44 isoform switch regulated epithelial-to-mesenchymal plasticity as standard form of CD44 and CD44v8-10 determined invasive and tumorigenic phenotypes, respectively. We have established a mechanistic link between TAMs and CSCs in HNSCC that is mediated by CD44 intracellular signaling in response to extracellular signals. SIGNIFICANCE: These findings establish a mechanistic link between tumor cell CD44, TAM, and CSC properties at the tumor-stroma interface that can serve as a vital area of focus for target and drug discovery.

Syndecan-1-Dependent Regulation of Heparanase Affects Invasiveness, Stem Cell Properties, and Therapeutic Resistance of Caco2 Colon Cancer Cells.

The heparan sulfate proteoglycan Syndecan-1 binds cytokines, morphogens and extracellular matrix components, regulating cancer stem cell properties and invasiveness. Syndecan-1 is modulated by the heparan sulfate-degrading enzyme heparanase, but the underlying regulatory mechanisms are only poorly understood. In colon cancer pathogenesis, complex changes occur in the expression pattern of Syndecan-1 and heparanase during progression from well-differentiated to undifferentiated tumors. Loss of Syndecan-1 and increased expression of heparanase are associated with a change in phenotypic plasticity and an increase in invasiveness, metastasis and dedifferentiation. Here we investigated the regulatory and functional interplay of Syndecan-1 and heparanase employing siRNA-mediated silencing and plasmid-based overexpression approaches in the human colon cancer cell line Caco2. Heparanase expression and activity were upregulated in Syndecan-1 depleted cells. This increase was linked to an upregulation of the transcription factor Egr1, which regulates heparanase at the promoter level. Inhibitor experiments demonstrated an impact of focal adhesion kinase, Wnt and ROCK-dependent signaling on this process. siRNA-depletion of Syndecan-1, and upregulation of heparanase increased the colon cancer stem cell phenotype based on sphere formation assays and phenotypic marker analysis (Side-population, NANOG, KLF4, NOTCH, Wnt, and TCF4 expression). Syndecan-1 depletion increased invasiveness of Caco2 cells in vitro in a heparanase-dependent manner. Finally, upregulated expression of heparanase resulted in increased resistance to radiotherapy, whereas high expression of enzymatically inactive heparanase promoted chemoresistance to paclitaxel and cisplatin. Our findings provide a new avenue to target a stemness-associated signaling axis as a therapeutic strategy to reduce metastatic spread and cancer recurrence.

Regulation of cancer stem cell properties, angiogenesis, and vasculogenic mimicry by miR-450a-5p/SOX2 axis in colorectal cancer

Growing evidence indicates that a small number of cancer cells express stem cell markers and possess stem cell-like properties that promote malignant progression. Sex-determining region Y-box2 (SOX2) is a stem cell transcription factor essential for maintaining the properties of cancer stem cell (CSC). As CSC properties have been associated with angiogenesis and vasculogenic mimicry (VM), we aimed to comprehensively investigate whether SOX2 regulates CSC properties, angiogenesis, and VM in colorectal carcinoma (CRC) and its potential mechanism in this study. For this study, sphere formation assay, flow cytometry, cell survival analysis, tube formation, 3D culture, immunoblot, mouse model, and luciferase reporter assay were performed in vivo and in vitro. Expressions of SOX2 and miR-450a-5p in CRC tissue samples were examined through immunohistochemistry. First, the expression of SOX2 was not only associated with poor differentiation and prognosis but also promoted angiogenesis and VM. Knockdown of SOX2 ceased stemness properties, angiogenesis, and VM, along with decreased expression of CD133, CD31, and VE-cadherin as observed in functional experiments. Downregulation of SOX2 was found to inhibit tumorigenesis in vivo. Second, miR-450a-5p suppressed the expression of SOX2 by targeting its 3’UTR region directly and hence restrained SOX2-induced CSC properties, angiogenesis, and VM. Moreover, SOX2 overexpression preserved the miR-450a-5p-induced inhibition of CRC properties, angiogenesis, and VM. Finally, clinical samples exhibited a negative correlation between miR-450a-5p and SOX2. Patients with higher SOX2 and lower miR-450a-5p expressions had a poorer prognosis than patients with inverse expressions. Conclusively, we elucidated a unique mechanism of miR-450a-5p-SOX2 axis in the regulation of stemness, angiogenesis, and VM, which may act as a potential therapeutic practice in CRC.

α-Actinin-4 regulates cancer stem cell properties and chemoresistance in cervical cancer.

Cancer stem cells (CSCs) initiate tumors and possess the properties of self-renewal and differentiation. Since they are responsible for chemoresistance, CSCs are known to be a key factor in cancer recurrence. α-Actinin-4 (ACTN4) is an actin-binding protein that is involved in muscle differentiation and cancer metastasis. It promotes epithelial to mesenchymal transition and cell cycle progression via β-catenin stabilization in cervical cancer. In the present study, we investigated the role of ACTN4 in regulating cancer cell stemness and chemoresistance in cervical cancer. Results from the gene expression database analysis showed that ACTN4 mRNA expression was elevated in cancerous cervices when compared with normal cervices. Furthermore, ACTN4 knockdown suppressed sphere formation and CSC proliferation. It also decreased CSC size and CD44high/CD24low cell population. ACTN4-knockdown CSCs were sensitive to anticancer drugs, which was observed by down-regulation of the ATP-binding cassette family G2 involved in drug resistance. Finally, ACTN4-knockdown CSCs formed reduced tumors in vivo when compared with control CSCs. Overall, these findings suggest that ACTN4 regulates CSC properties and contributes to chemoresistance in cervical cancer.

The expanding roles of long non-coding RNAs in the regulation of cancer stem cells.

Long non-coding RNAs (lncRNAs) are a novel class of gene regulators playing multifaceted roles in physiological processes as well as pathological conditions such as cancer. Cancer stem cells (CSCs) are a small subset of tumor cells that constitute the origin and development of various malignant tumors. CSCs have been identified in a wide spectrum of human tumors and could act as a critical link underlying the processes of tumor metastasis and recurrence. Mounting evidence indicates that lncRNAs are aberrantly expressed in diverse CSCs and regulate CSC properties at different molecular levels. Here, we very briefly summarize the recent findings on the potential roles of lncRNAs in regulating various functions of CSCs, and elaborate on how can lncRNAs impact CSC properties via interacting with other macromolecules at the epigenetic, transcriptional, and post-transcriptional levels. This mini-review also highlights the understanding of the modular regulatory principles of lncRNA interactions in CSCs.

Suppression of Breast Cancer Stem Cells and Tumor Growth by the RUNX1 Transcription Factor.

Breast cancer remains the most common malignant disease in women worldwide. Despite advances in detection and therapies, studies are still needed to understand the mechanisms underlying this cancer. Cancer stem cells (CSC) play an important role in tumor formation, growth, drug resistance, and recurrence. Here, it is demonstrated that the transcription factor RUNX1, well known as essential for hematopoietic differentiation, represses the breast cancer stem cell (BCSC) phenotype and suppresses tumor growth in vivo. The current studies show that BCSCs sorted from premalignant breast cancer cells exhibit decreased RUNX1 levels, whereas ectopic expression of RUNX1 suppresses tumorsphere formation and reduces the BCSC population. RUNX1 ectopic expression in breast cancer cells reduces migration, invasion, and in vivo tumor growth (57%) in mouse mammary fat pad. Mechanistically, RUNX1 functions to suppress breast cancer tumor growth through repression of CSC activity and direct inhibition of ZEB1 expression. Consistent with these cellular and biochemical results, clinical findings using patient specimens reveal that the highest RUNX1 levels occur in normal mammary epithelial cells and that low RUNX1 expression in tumors is associated with poor patient survival. IMPLICATIONS: The key finding that RUNX1 represses stemness in several breast cancer cell lines points to the importance of RUNX1 in other solid tumors where RUNX1 may regulate CSC properties.

Abstract 3067: The novel function of keratin 14 (KRT14) in regulating cancer stem cell properties in lung adenocarcinoma

Abstract Lung cancer remains the leading cause of cancer deaths worldwide. Among all classification subtypes, lung adenocarcinoma (LUAD) accounts for the largest proportion of all cases of lung cancer. Although the expanding development of novel targeted therapies has been improving the overall survival of lung cancer patients, recurrence and therapeutic resistance remains as the major reasons of treatment failure. Cancer stem cells (CSCs) have been revealed to be one of the major drivers for tumor recurrence and therapeutic resistance. Understanding the molecular pathways in regulating CSCs may provide insights on designing novel drug combinations in targeting the disease. Various studies showed that there is a contrasting expression of keratins in stem and differentiated cells, implying the functional importance of keratins in maintaining stem cell characteristics. Keratin 14 (KRT14) is a keratin isoform shown to be enriched in breast and bladder CSCs. In LUAD, KRT14 has been reported to be a key player in tumor invasion, yet its role in regulating LUAD CSCs remains largely unknown. In this study, we aim to delineate the clinical significance and the functional role of KRT14in LUAD. From The Cancer Genome Atlas (TCGA) data, the mRNA expression of KRT14 was found to be higher in LUAD tumor when compared with paired normal tissues (p=0.0057).This data was also confirmed in protein level with our in-house cohort, in which LUAD tumor showed an upregulation of KRT14 protein expression. TCGA data also revealed that patients with high KRT14 mRNA expression have a poorer disease-free survival (p=0.0147) and overall survival (p=0.0043). By qPCR and western blot analyses, we found that the expression of KRT14 is upregulated in our established enriched lung CSC population. Using lenti-viral based knockdown approach, KRT14 was found to regulate the traits of CSCs, including tumorigenicity, self-renewal, drug resistance and the expression of lung CSC markers. Interestingly, KRT14 was found to be upregulated in the erlotinib-resistant LUAD cells, and the abrogation of KRT14 expression re-sensitized these cells to erlotinib treatment. The genetic profiles of KRT14 knockdown and control cells will be compared in the future to identify the potential downstream targets of KRT14 in regulating lung CSCs. In summary, our study highlights the crucial role of KRT14 in maintaining lung CSCs and may provide a novel therapeutic target for the disease. Citation Format: Isabella Kit-Nam Chin, Goretti Hoi-Yan Cheung, Hazel Yuk-Yan Kwok, Victor Wan-San Ma, Eunice Yuen-Ting Lau, William Chi-Shing Cho. The novel function of keratin 14 (KRT14) in regulating cancer stem cell properties in lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3067.

Abstract 1118: DOT1L epigenetically regulates cancer stem cell properties and tumor progression in glioblastoma brain tumor stem cells

Abstract The median survival for patients diagnosed with Glioblastoma (GBM) is only 14 months, due to recurrence, despite current treatment options of surgery, radio- and chemo-therapies. Brain tumor stem cells (BTSCs) are thought to underlie disease recurrence and lethality as they exhibit self-renewal, multipotency and tumorigenesis. The epigenetic regulation of BTSCs are relatively un-characterized and unlike genomic mutations are potentially reversible. Disrupter of telomeric silencing-1-like (DOT1L) is the only known histone methyltransferase responsible for histone-3-lysine-79 methylation (H3K79me), an epigenetic mark associated with active gene transcription. Previous studies investigating the therapeutic implications of targeting DOT1L in cancer have shown that its inhibition in leukemia results in cancer cell death and, in solid cancers, decreases metastasis. We investigated the role of DOT1L in GBM BTSCs. We find that short-term DOT1L inhibition in BTSCs in vitro has limited effects on viability but alters growth morphology, as neurospheres become flattened and adherent. Furthermore, inhibition decreases BTSC invasion and promotes differentiation. Long-term inhibition of DOT1L had a more pronounced effect on sphere morphology and decreased BTSC proliferation and survival. Pre-treatment with the DOT1L inhibitor EPZ-5676 followed by orthotopic xenografts of BTSCs led to slowed tumor growth and improved overall survival. Initial H3K79me2 ChIP-sequencing and RNA-sequencing results show that H3K79me2 levels and gene expression are decreased for stem and progenitor cell markers SOX2 and OLIG2 respectively, in BTSCs treated with EPZ-5676. These results suggest that DOT1L may be an important regulator of GBM cancer stem cell properties and tumor progression. Current studies aim to further investigate how DOT1L regulates BTSCs by overlaying H3K79me2 ChIP-sequencing, RNA-sequencing and ATAC-sequencing in a panel of BTSCs following DOT1L inhibition and overexpression. These findings highlight the potential clinical implications of epigenetic targeted therapies for GBM. Citation Format: Danielle Bozek, Xiaoguang Hao, H. Artee Luchman, Samuel Weiss. DOT1L epigenetically regulates cancer stem cell properties and tumor progression in glioblastoma brain tumor stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1118.

The Critical, Clinical Role of Interferon-Beta in Regulating Cancer Stem Cell Properties in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) the deadliest form of this disease currently lacks a targeted therapy and is characterized by increased risk of metastasis and presence of therapeutically resistant cancer stem cells (CSC). Recent evidence has demonstrated that the presence of an interferon (IFN)/signal transducer of activated transcription 1 (STAT1) gene signature correlates with improved therapeutic response and overall survival in TNBC patients. In agreement with these clinical observations, our recent work has demonstrated, in a cell model of TNBC that CSC have intrinsically repressed IFN signaling. Administration of IFN-β represses CSC properties, inducing a less aggressive non-CSC state. Moreover, an elevated IFN-β gene signature correlated with repressed CSC-related genes and an increased presence of tumor-infiltrating lymphocytes in TNBC specimens. We therefore propose that IFN-β be considered as a potential therapeutic option in the treatment of TNBC, to repress the CSC properties responsible for therapy failure. Future studies aim to improve methods to target delivery of IFN-β to tumors, to maximize therapeutic efficacy while minimizing systemic side effects.

SOX10 induced Nestin expression regulates cancer stem cell properties of TNBC cells

The mechanisms modulating the cancer stem cell (CSC) properties of triple negative breast cancer (TNBC) cells were not fully understood. In this study, we performed data mining in Breast Cancer Gene-Expression Miner v4.0 and found that TNBC tumors had significantly higher NES mRNA expression than other breast cancer subtypes. Pooled data suggested that NES mRNA expression is associated worse metastatic relapse (MR) free survival and also worse any event (AE) free survival in TNBC patients. Following data mining in multiple big data databases confirmed a positive correlation between SOX10 mRNA expression and NES mRNA expression in breast cancer tissues. In addition, the expression of SOX10 mRNA is significantly higher in TNBC tissues than in other breast cancer subtypes. SOX10 overexpression resulted in Nestin upregulation at both mRNA and protein levels. Bioinformatic analysis predicted a SOX10 binding site in NES promoter and the following dual luciferase assay verified the binding site. Functionally, SOX10 overexpression substantially increased CSC properties of TNBC cells, while SOX10 knockdown decreased the CSC properties, in terms of CD24-/CD44+ cell ratio and tumorsphere-forming capabilities. Enforced Nestin expression partly counteracted the effect of SOX10 knockdown on reducing the CSC properties. Based on these findings, we infer that SOX10 regulates cancer stem cell properties of TNBC cells via inducing Nestin expression.