MUC1-C activates EZH2 expression and function in human cancer cells

MUC1-C regulates NEAT1 lncRNA expression and paraspeckle formation in cancer progression

The MUC1 gene evolved in mammals for adaptation of barrier tissues in response to infections and damage. Paraspeckles are nuclear bodies formed on the NEAT1 lncRNA in response to loss of homeostasis. There is no known intersection of MUC1 with NEAT1 or paraspeckles. Here, we demonstrate that the MUC1-C subunit plays an essential role in regulating NEAT1 expression. MUC1-C activates the NEAT1 gene with induction of the NEAT1_1 and NEAT1_2 isoforms by NF-κB- and MYC-mediated mechanisms. MUC1-C/MYC signaling also induces expression of the SFPQ, NONO and FUS RNA binding proteins (RBPs) that associate with NEAT1_2 and are necessary for paraspeckle formation. MUC1-C integrates activation of NEAT1 and RBP-encoding genes by recruiting the PBAF chromatin remodeling complex and increasing chromatin accessibility of their respective regulatory regions. We further demonstrate that MUC1-C and NEAT1 form an auto-inductive pathway that drives common sets of genes conferring responses to inflammation and loss of homeostasis. Of functional significance, we find that the MUC1-C/NEAT1 pathway is of importance for the cancer stem cell (CSC) state and anti-cancer drug resistance. These findings identify a previously unrecognized role for MUC1-C in the regulation of NEAT1, RBPs, and paraspeckles that has been co-opted in promoting cancer progression.

XIST and MUC1-C form an auto-regulatory pathway in driving cancer progression

The long non-coding RNA X-inactive specific transcript (lncRNA XIST) and MUC1 gene are dysregulated in chronic inflammation and cancer; however, there is no known interaction of their functions. The present studies demonstrate that MUC1-C regulates XIST lncRNA levels by suppressing the RBM15/B, WTAP and METTL3/14 components of the m6A methylation complex that associate with XIST A repeats. MUC1-C also suppresses the YTHDF2-CNOT1 deadenylase complex that recognizes m6A sites and contributes to XIST decay with increases in XIST stability and expression. In support of an auto-regulatory pathway, we show that XIST regulates MUC1-C expression by promoting NF-κB-mediated activation of the MUC1 gene. Of significance, MUC1-C and XIST regulate common genes associated with inflammation and stemness, including (i) miR-21 which is upregulated across pan-cancers, and (ii) TDP-43 which associates with the XIST E repeats. Our results further demonstrate that the MUC1-C/XIST pathway (i) is regulated by TDP-43, (ii) drives stemness-associated genes, and (iii) is necessary for self-renewal capacity. These findings indicate that the MUC1-C/XIST auto-regulatory axis is of importance in cancer progression.

A mechanistic insight on how Compromised Hydrolysis of Triacylglycerol 7 (CHT7) restrains the involvement of it's CXC domain from quiescence repression

CHT7 is a regulator of quiescence repression in Chlamydomonas reinhardtii. Initially, CHT7's repression activity was thought to be managed by its DNA-binding CXC domain. Later, it was found that the CHT7-CXC domain is dispensable for CHT7's activities. Rather, CHT7's predicted protein domains were proposed to be involved in regulation activities by binding to other repressors in the cell. Yet, it remains unclear why and how CHT7 refrains its CXC domain from participating in any transcriptional activities. The question becomes more intriguing, since CXC binding regions are available in promoter regions of some of the misregulated genes in CHT7 mutant (cht7). Through biophysical experiments and molecular dynamics approaches, we studied the DNA recognition behavior of CHT7-CXC. The results indicate that this domain possesses sequence selectivity due to the differential binding abilities of its subdomains. Further, to understand if the case is that CXC loses its DNA binding capabilities in the vicinity of other repressors, we examined CHT7-CXC's DNA binding stability under the spatial constraint conditions created through fusing CHT7-CXC with AsLOV2. The results show limited ability of CHT7-CXC to withstand steric forces and provide insights to why and how algal cells may hold back CHT7-CXC's indulgence in quiescence repression. CLASSIFICATIONS: Biological Sciences, Biophysics and Computational Biology.

MUC1-C intersects chronic inflammation with epigenetic reprogramming by regulating the set1a compass complex in cancer progression

Chronic inflammation promotes epigenetic reprogramming in cancer progression by pathways that remain unclear. The oncogenic MUC1-C protein is activated by the inflammatory NF-κB pathway in cancer cells. There is no known involvement of MUC1-C in regulation of the COMPASS family of H3K4 methyltransferases. We find that MUC1-C regulates (i) bulk H3K4 methylation levels, and (ii) the COMPASS SET1A/SETD1A and WDR5 genes by an NF-κB-mediated mechanism. The importance of MUC1-C in regulating the SET1A COMPASS complex is supported by the demonstration that MUC1-C and WDR5 drive expression of FOS, ATF3 and other AP-1 family members. In a feedforward loop, MUC1-C, WDR5 and AP-1 contribute to activation of genes encoding TRAF1, RELB and other effectors in the chronic NF-κB inflammatory response. We also show that MUC1-C, NF-κB, WDR5 and AP-1 are necessary for expression of the (i) KLF4 master regulator of the pluripotency network and (ii) NOTCH1 effector of stemness. In this way, MUC1-C/NF-κB complexes recruit SET1A/WDR5 and AP-1 to enhancer-like signatures in the KLF4 and NOTCH1 genes with increases in H3K4me3 levels, chromatin accessibility and transcription. These findings indicate that MUC1-C regulates the SET1A COMPASS complex and the induction of genes that integrate NF-κB-mediated chronic inflammation with cancer progression.

The multifaceted role of MUC1 in tumor therapy resistance

Tumor therapeutic resistances are frequently linked to the recurrence and poor prognosis of cancers and have been a key bottleneck in clinical tumor treatment. Mucin1 (MUC1), a heterodimeric transmembrane glycoprotein, exhibits abnormally overexpression in a variety of human tumors and has been confirmed to be related to the formation of therapeutic resistance. In this review, the multifaceted roles of MUC1 in tumor therapy resistance are summarized from aspects of pan-cancer principles shared among therapies and individual mechanisms dependent on different therapies. Concretely, the common mechanisms of therapy resistance across cancers include interfering with gene expression, promoting genome instability, modifying tumor microenvironment, enhancing cancer heterogeneity and stemness, and activating evasion and metastasis. Moreover, the individual mechanisms of therapy resistance in chemotherapy, radiotherapy, and biotherapy are introduced. Last but not least, MUC1-involved therapy resistance in different types of cancers and MUC1-related clinical trials are summarized.

Dependence on MUC1-C in Progression of Neuroendocrine Prostate Cancer

Castration resistant prostate cancer (CRPC) is responsive to androgen receptor (AR) axis targeted agents; however, patients invariably relapse with resistant disease that often progresses to neuroendocrine prostate cancer (NEPC). Treatment-related NEPC (t-NEPC) is highly aggressive with limited therapeutic options and poor survival outcomes. The molecular basis for NEPC progression remains incompletely understood. The MUC1 gene evolved in mammals to protect barrier tissues from loss of homeostasis. MUC1 encodes the transmembrane MUC1-C subunit, which is activated by inflammation and contributes to wound repair. However, chronic activation of MUC1-C contributes to lineage plasticity and carcinogenesis. Studies in human NEPC cell models have demonstrated that MUC1-C suppresses the AR axis and induces the Yamanaka OSKM pluripotency factors. MUC1-C interacts directly with MYC and activates the expression of the BRN2 neural transcription factor (TF) and other effectors, such as ASCL1, of the NE phenotype. MUC1-C also induces the NOTCH1 stemness TF in promoting the NEPC cancer stem cell (CSC) state. These MUC1-C-driven pathways are coupled with activation of the SWI/SNF embryonic stem BAF (esBAF) and polybromo-BAF (PBAF) chromatin remodeling complexes and global changes in chromatin architecture. The effects of MUC1-C on chromatin accessibility integrate the CSC state with the control of redox balance and induction of self-renewal capacity. Importantly, targeting MUC1-C inhibits NEPC self-renewal, tumorigenicity and therapeutic resistance. This dependence on MUC1-C extends to other NE carcinomas, such as SCLC and MCC, and identify MUC1-C as a target for the treatment of these aggressive malignancies with the anti-MUC1 agents now under clinical and preclinical development.

MUC1-C is a master regulator of MICA/B NKG2D ligand and exosome secretion in human cancer cells

BACKGROUND

The MUC1-C protein evolved in mammals to protect barrier tissues from loss of homeostasis; however, MUC1-C promotes oncogenesis in association with chronic inflammation. Aberrant expression of MUC1-C in cancers has been linked to depletion and dysfunction of T cells in the tumor microenvironment. In contrast, there is no known involvement of MUC1-C in the regulation of natural killer (NK) cell function.

METHODS

Targeting MUC1-C genetically and pharmacologically in cancer cells was performed to assess effects on intracellular and cell surface expression of the MHC class I chain-related polypeptide A (MICA) and MICB ligands. The MICA/B promoters were analyzed for H3K27 and DNA methylation. Shedding of MICA/B was determined by ELISA. MUC1-C interactions with ERp5 and RAB27A were assessed by coimmunoprecipitation and direct binding studies. Exosomes were isolated for analysis of secretion. Purified NK cells were assayed for killing of cancer cell targets.

RESULTS

Our studies demonstrate that MUC1-C represses expression of the MICA and MICB ligands that activate the NK group 2D receptor. We show that the inflammatory MUC1-C→NF-κB pathway drives enhancer of zeste homolog 2-mediated and DNMT-mediated methylation of the MICA and MICB promoter regions. Targeting MUC1-C genetically and pharmacologically with the GO-203 inhibitor induced intracellular and cell surface MICA/B expression but not MICA/B cleavage. Mechanistically, MUC1-C regulates the ERp5 thiol oxidoreductase that is necessary for MICA/B protease digestion and shedding. In addition, MUC1-C interacts with the RAB27A protein, which is required for exosome formation and secretion. As a result, targeting MUC1-C markedly inhibited secretion of exosomes expressing MICA/B. In concert with these results, we show that targeting MUC1-C promotes NK cell-mediated killing.

CONCLUSIONS

These findings uncover pleotropic mechanisms by which MUC1-C confers evasion of cancer cells to NK cell recognition and destruction.

Docetaxel Enhances Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand-Mediated Apoptosis in Prostate Cancer Cells via Epigenetic Gene Regulation by Enhancer of Zeste Homolog 2

PURPOSE

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising cancer therapeutic agent because of its tumor selectivity and its ability to induce apoptosis in cancer cells while sparing most normal cells. We evaluated whether docetaxel enhances TRAIL-mediated apoptosis in prostate cancer (PCa) cells and its mechanism.

MATERIALS AND METHODS

LNCap-LN3, PC3, and DU 145 PCa cell lines were used to investigate the effects of TRAIL with docetaxel treatment (dosages, 1, 3, 5, and 10 nmol). To evaluate the mechanism, death receptor 4 (DR4), DR5, enhancer of zeste homolog 2 (EZH2) and E2F1 levels were assessed in PCa cells.

RESULTS

Hormone-sensitive LNCap-LN3 showed apoptosis in proportion to the concentration of docetaxel. Castration-resistant PC3 and DU 145 showed no change irrespective of the docetaxel concentration. However, combinations of docetaxel (2 nM) and TRAIL (100 ng/mL) had a significant effect on apoptosis of DU 145 cells. In DU 145 cells, docetaxel reduced EZH2 and elevated expression of DR4. The decrease of EZH2 by docetaxel was correlated with the E2F1 level, which was considered as the promoter of EZH2. DZNep reduced EZH2 and elevated DR4 in all PCa cells. Additionally, DZNep-enhanced TRAIL mediated reduction of PCa cell viability.

CONCLUSIONS

Docetaxel and the EZH2 inhibitor reduced EZH2 and elevated expression of DR4 in all PCa cell lines. Docetaxel-enhanced TRAIL mediated apoptosis in PCa via elevation of DR4 through epigenetic regulation by EZH2. To improve the efficacy of TRAIL for PCa treatment, adding docetaxel or EZH2 inhibitors to TRAIL may be promising.

MUC1 promotes glioblastoma progression and TMZ resistance by stabilizing EGFRvIII

Epidermal growth factor receptor variant III (EGFRvIII) is a mutant isoform of EGFR with a deletion of exons 2-7 making it insensitive to EGF stimulation and downstream signal constitutive activation. However, the mechanism underlying the stability of EGFRvIII remains unclear. Based on CRISPR-Cas9 library screening, we found that mucin1 (MUC1) is essential for EGFRvIII glioma cell survival and temozolomide (TMZ) resistance. We revealed that MUC1-C was upregulated in EGFRvIII-positive cells, where it enhanced the stability of EGFRvIII. Knockdown of MUC1-C increased the colocalization of EGFRvIII and lysosomes. Upregulation of MUC1 occurred in an NF-κB dependent manner, and inhibition of the NF-κB pathway could interrupt the EGFRvIII-MUC1 feedback loop by inhibiting MUC1-C. In a previous report, we identified AC1Q3QWB (AQB), a small molecule that could inhibit the phosphorylation of NF-κB. By screening the structural analogs of AQB, we obtained EPIC-1027, which could inhibit the NF-κB pathway more effectively. EPIC-1027 disrupted the EGFRvIII-MUC1-C positive feedback loop in vitro and in vivo, inhibited glioma progression, and promoted sensitization to TMZ. In conclusion, we revealed the pivotal role of MUC1-C in stabilizing EGFRvIII in glioblastoma (GBM) and identified a small molecule, EPIC-1027, with great potential in GBM treatment.

Emergence of MUC1 in Mammals for Adaptation of Barrier Epithelia

The mucin 1 (MUC1) gene was discovered based on its overexpression in human breast cancers. Subsequent work demonstrated that MUC1 is aberrantly expressed in cancers originating from other diverse organs, including skin and immune cells. These findings supported a role for MUC1 in the adaptation of barrier tissues to infection and environmental stress. Of fundamental importance for this evolutionary adaptation was inclusion of a SEA domain, which catalyzes autoproteolysis of the MUC1 protein and formation of a non-covalent heterodimeric complex. The resulting MUC1 heterodimer is poised at the apical cell membrane to respond to loss of homeostasis. Disruption of the complex releases the MUC1 N-terminal (MUC1-N) subunit into a protective mucous gel. Conversely, the transmembrane C-terminal (MUC1-C) subunit activates a program of lineage plasticity, epigenetic reprogramming and repair. This MUC1-C-activated program apparently evolved for barrier tissues to mount self-regulating proliferative, inflammatory and remodeling responses associated with wound healing. Emerging evidence indicates that MUC1-C underpins inflammatory adaptation of tissue stem cells and immune cells in the barrier niche. This review focuses on how prolonged activation of MUC1-C by chronic inflammation in these niches promotes the cancer stem cell (CSC) state by establishing auto-inductive nodes that drive self-renewal and tumorigenicity.

Addiction of Cancer Stem Cells to MUC1-C in Triple-Negative Breast Cancer Progression

Triple-negative breast cancer (TNBC) is an aggressive malignancy with limited treatment options. TNBC progression is associated with expansion of cancer stem cells (CSCs). Few insights are available regarding druggable targets that drive the TNBC CSC state. This review summarizes the literature on TNBC CSCs and the compelling evidence that they are addicted to the MUC1-C transmembrane protein. In normal epithelia, MUC1-C is activated by loss of homeostasis and induces reversible wound-healing responses of inflammation and repair. However, in settings of chronic inflammation, MUC1-C promotes carcinogenesis. MUC1-C induces EMT, epigenetic reprogramming and chromatin remodeling in TNBC CSCs, which are dependent on MUC1-C for self-renewal and tumorigenicity. MUC1-C-induced lineage plasticity in TNBC CSCs confers DNA damage resistance and immune evasion by chronic activation of inflammatory pathways and global changes in chromatin architecture. Of therapeutic significance, an antibody generated against the MUC1-C extracellular domain has been advanced in a clinical trial of anti-MUC1-C CAR T cells and in IND-enabling studies for development as an antibody-drug conjugate (ADC). Agents targeting the MUC1-C cytoplasmic domain have also entered the clinic and are undergoing further development as candidates for advancing TNBC treatment. Eliminating TNBC CSCs will be necessary for curing this recalcitrant cancer and MUC1-C represents a promising druggable target for achieving that goal.

Chronic activation of MUC1-C in wound repair promotes progression to cancer stem cells

The mucin 1 (MUC1) gene emerged in mammals to afford protection of barrier epithelial tissues from the external environment. MUC1 encodes a transmembrane C-terminal (MUC1-C) subunit that is activated by loss of homeostasis and induces inflammatory, proliferative, and remodeling pathways associated with wound repair. As a consequence, chronic activation of MUC1-C promotes lineage plasticity, epigenetic reprogramming, and carcinogenesis. In driving cancer progression, MUC1-C is imported into the nucleus, where it induces NF-κB inflammatory signaling and the epithelial-mesenchymal transition (EMT). MUC1-C represses gene expression by activating (i) DNA methyltransferase 1 (DNMT1) and DNMT3b, (ii) Polycomb Repressive Complex 1 (PRC1) and PRC2, and (iii) the nucleosome remodeling and deacetylase (NuRD) complex. PRC1/2-mediated gene repression is counteracted by the SWI/SNF chromatin remodeling complexes. MUC1-C activates the SWI/SNF BAF and PBAF complexes in cancer stem cell (CSC) models with the induction of genome-wide differentially accessible regions and expressed genes. MUC1-C regulates chromatin accessibility of enhancer-like signatures in association with the induction of the Yamanaka pluripotency factors and recruitment of JUN and BAF, which promote increases in histone activation marks and opening of chromatin. These and other findings described in this review have uncovered a pivotal role for MUC1-C in integrating lineage plasticity and epigenetic reprogramming, which are transient in wound repair and sustained in promoting CSC progression.

MUC1-C Dictates JUN and BAF-Mediated Chromatin Remodeling at Enhancer Signatures in Cancer Stem Cells

The oncogenic MUC1-C protein promotes dedifferentiation of castrate-resistant prostate cancer (CRPC) and triple-negative breast cancer (TNBC) cells. Chromatin remodeling is critical for the cancer stem cell (CSC) state; however, there is no definitive evidence that MUC1-C regulates chromatin accessibility and thereby expression of stemness-associated genes. We demonstrate that MUC1-C drives global changes in chromatin architecture in the dedifferentiation of CRPC and TNBC cells. Our results show that MUC1-C induces differentially accessible regions (DAR) across their genomes, which are significantly associated with differentially expressed genes (DEG). Motif and cistrome analysis further demonstrated MUC1-C-induced DARs align with genes regulated by the JUN/AP-1 family of transcription factors. MUC1-C activates the BAF chromatin remodeling complex, which is recruited by JUN in enhancer selection. In studies of the NOTCH1 gene, which is required for CRPC and TNBC cell self-renewal, we demonstrate that MUC1-C is necessary for (i) occupancy of JUN and ARID1A/BAF, (ii) increases in H3K27ac and H3K4me3 signals, and (iii) opening of chromatin accessibility on a proximal enhancer-like signature. Studies of the EGR1 and LY6E stemness-associated genes further demonstrate that MUC1-C-induced JUN/ARID1A complexes regulate chromatin accessibility on proximal and distal enhancer-like signatures. These findings uncover a role for MUC1-C in chromatin remodeling that is mediated at least in part by JUN/AP-1 and ARID1A/BAF in association with driving the CSC state.

IMPLICATIONS

These findings show that MUC1-C, which is necessary for the CRPC and TNBC CSC state, activates a novel pathway involving JUN/AP-1 and ARID1A/BAF that regulates chromatin accessibility of stemness-associated gene enhancers.

Emerging Roles of LncRNAs in the EZH2-regulated Oncogenic Network

Cancer is a life-threatening disease, but cancer therapies based on epigenetic mechanisms have made great progress. Enhancer of zeste homolog 2 (EZH2) is the key catalytic component of Polycomb repressive complex 2 (PRC2) that mediates the tri-methylation of lysine 27 on histone 3 (H3K27me3), a well-recognized marker of transcriptional repression. Mounting evidence indicates that EZH2 is elevated in various cancers and associates with poor prognosis. In addition, many studies revealed that EZH2 is also involved in transcriptional repression dependent or independent of PRC2. Meanwhile, long non-coding RNAs (lncRNAs) have been reported to regulate numerous and diverse signaling pathways in oncogenesis. In this review, we firstly discuss functional interactions between EZH2 and lncRNAs that determine PRC2-dependent and -independent roles of EZH2. Secondly, we summarize the lncRNAs regulating EZH2 expression at transcription, post-transcription and post-translation levels. Thirdly, we review several oncogenic pathways cooperatively regulated by lncRNAs and EZH2, including the Wnt/β-catenin and p53 pathways. In conclusion, lncRNAs play a key role in the EZH2-regulated oncogenic network with many fertile directions to be explored.

An NF-κB-responsive long noncoding RNA, PINT, regulates TNF-α gene transcription by scaffolding p65 and EZH2

Long noncoding RNAs (lncRNAs) are central regulators of the inflammatory response and play an important role in inflammatory diseases. PINT has been reported to be involved in embryonic development and tumorigenesis. However, the potential functions of PINT in the innate immune system are largely unknown. Here, we revealed the transcriptional regulation of inflammatory genes by PINT, whose expression is primarily dependent on the NF-κB signaling pathway in human and mouse macrophage and intestinal epithelial cell lines. Functionally, PINT selectively regulates the expression of TNF-α in basal and LPS-stimulated cells. Mechanistically, PINT acts as a modular scaffold of p65 and EZH2 to coordinate their localization and specify their binding to the target genes. Further, a high expression level of PINT was detected in intestinal mucosal tissues from patients with ulcerative colitis (UC). Together, these findings demonstrate that PINT acts as an activator of inflammatory responses, highlighting the importance of this lncRNA as a potential therapeutic target in infectious diseases and inflammatory diseases.

MUC1-C activates the PBAF chromatin remodeling complex in integrating redox balance with progression of human prostate cancer stem cells

The polybromo-associated PBAF (SWI/SNF) chromatin remodeling complex, which includes PBRM1, ARID2, and BRD7, regulates cell differentiation and genomic integrity. MUC1-C is an oncogenic protein that drives lineage plasticity in prostate cancer (PC) progression. The present work demonstrates that MUC1-C induces PBRM1, ARID2, and BRD7 expression by the previously unrecognized E2F1-mediated activation of their respective promoters. The functional significance of the MUC1-C→PBAF pathway is supported by demonstrating involvement of MUC1-C in associating with nuclear PBAF and driving the NRF2 antioxidant gene transcriptome in PC cells. Mechanistically, MUC1-C forms a complex with NRF2 and PBRM1 on the NRF2 target SLC7A11 gene that encodes the xCT cystine-glutamate antiporter, increases chromatin accessibility and induces SLC7A11/xCT expression. We also show that MUC1-C and PBRM1 are necessary for induction of other NRF2 target genes, including G6PD and PGD that regulate the pentose phosphate pathway. Our results further demonstrate that MUC1-C integrates activation of PBRM1 with the regulation of antioxidant genes, ROS levels, pluripotency factor expression and the cancer stem cell (CSC) state. These findings reveal a role for MUC1-C in regulating PBAF, redox balance and lineage plasticity of PC CSC progression. Our findings also uncover involvement of MUC1-C in integrating the PBAF and BAF pathways in cancer.

Overcoming Immune Checkpoint Blockade Resistance via EZH2 Inhibition

Recent progress in cancer immunotherapy highlights the power of the immune system to control tumors, although a small patient subset responds to current immunotherapies. Additional approaches to mobilize antitumor immunity are required to overcome primary and acquired resistance to immunotherapy such as immune checkpoint blockade (ICB). Emerging evidence shows that targeting epigenetic elements that promote tumor progression and inhibit immune cell activity can enhance antitumor immunity by reshaping the tumor microenvironment (TME). Here, we review the pleiotropic functions in tumor and immune cells of enhancer of zeste homolog 2 (EZH2), the catalytic subunit of polycomb repressive complex 2 (PRC2), with a focus on EZH2 inhibition as a potentially promising approach to enhance current immunotherapies and improve patient outcomes for certain cancers.

Regulation of breast cancer metastasis signaling by miRNAs

Despite the decline in death rate from breast cancer and recent advances in targeted therapies and combinations for the treatment of metastatic disease, metastatic breast cancer remains the second leading cause of cancer-associated death in U.S. women. The invasion-metastasis cascade involves a number of steps and multitudes of proteins and signaling molecules. The pathways include invasion, intravasation, circulation, extravasation, infiltration into a distant site to form a metastatic niche, and micrometastasis formation in a new environment. Each of these processes is regulated by changes in gene expression. Noncoding RNAs including microRNAs (miRNAs) are involved in breast cancer tumorigenesis, progression, and metastasis by post-transcriptional regulation of target gene expression. miRNAs can stimulate oncogenesis (oncomiRs), inhibit tumor growth (tumor suppressors or miRsupps), and regulate gene targets in metastasis (metastamiRs). The goal of this review is to summarize some of the key miRNAs that regulate genes and pathways involved in metastatic breast cancer with an emphasis on estrogen receptor α (ERα+) breast cancer. We reviewed the identity, regulation, human breast tumor expression, and reported prognostic significance of miRNAs that have been documented to directly target key genes in pathways, including epithelial-to-mesenchymal transition (EMT) contributing to the metastatic cascade. We critically evaluated the evidence for metastamiRs and their targets and miRNA regulation of metastasis suppressor genes in breast cancer progression and metastasis. It is clear that our understanding of miRNA regulation of targets in metastasis is incomplete.

MUC1-C Activates the BAF (mSWI/SNF) Complex in Prostate Cancer Stem Cells

The Brg/Brahma-associated factor (BAF, mSWI/SNF) chromatin remodeling complex is of importance in development and has been linked to prostate oncogenesis. The oncogenic MUC1-C protein promotes lineage plasticity in the progression of neuroendocrine prostate cancer (NEPC), however, there is no known association between MUC1-C and BAF. We report here that MUC1-C binds directly to the E2F1 transcription factor and that the MUC1-C→E2F1 pathway induces expression of embryonic stem cell-specific BAF (esBAF) components BRG1, ARID1A, BAF60a, BAF155, and BAF170 in castrate-resistant prostate cancer (CRPC) and NEPC cells. In concert with this previously unrecognized pathway, MUC1 was associated with increased expression of E2F1 and esBAF components in NEPC tumors as compared with CRPC, supporting involvement of MUC1-C in activating the E2F1→esBAF pathway with progression to NEPC. MUC1-C formed a nuclear complex with BAF and activated cancer stem cell (CSC) gene signatures and the core pluripotency factor gene network. The MUC1-C→E2F1→BAF pathway was necessary for induction of both the NOTCH1 effector of CSC function and the NANOG pluripotency factor, and collectively, this network drove CSC self-renewal. These findings indicate that MUC1-C promotes NEPC progression by integrating activation of E2F1 and esBAF with induction of NOTCH1, NANOG, and stemness. SIGNIFICANCE: These findings show that MUC1-C, which promotes prostate cancer progression, activates a novel pathway that drives the BAF remodeling complex, induces NOTCH1 and NANOG, and promotes self-renewal of prostate cancer stem cells.

MUC1-C drives stemness in progression of colitis to colorectal cancer

Colitis is associated with the development of colorectal cancer (CRC) by largely undefined mechanisms that are critical for understanding the link between inflammation and cancer. Intestinal stem cells (ISCs) marked by leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) expression are of importance in both the inflammatory response to colitis and progression to colitis-associated colon cancer (CACC). Here, we report in human mucin 1-transgenic (MUC1-transgenic) mouse models of CACC, targeting the MUC1-C oncogenic protein suppresses the (a) Lgr5+ ISC population, (b) induction of Myc and core pluripotency stem cell factors, and (c) severity and progression of colitis to dysplasia and cancer. By extension to human colon cancer cells, we demonstrate that MUC1-C drives MYC, forms a complex with MYC on the LGR5 promoter, and activates LGR5 expression. We also show in CRC cells that MUC1-C induces cancer stem cell (CSC) markers (BMI1, ALDH1, FOXA1, LIN28B) and the OCT4, SOX2, and NANOG pluripotency factors. Consistent with conferring the CSC state, targeting MUC1-C suppresses the capacity of CRC cells to promote wound healing, invasion, self-renewal, and tumorigenicity. In analysis of human tissues, MUC1 expression associates with activation of inflammatory pathways, development of colitis, and aggressiveness of CRCs. These results collectively indicate that MUC1-C is of importance for integrating stemness and pluripotency in colitis and CRC. Of clinical relevance, the findings further indicate that MUC1-C represents a potentially previously unrecognized target that is druggable for treating progression of colitis and CRC.

High level of EZH2 expression is linked to high density of CD8-positive T-lymphocytes and an aggressive phenotype in renal cell carcinoma

Purpose

Enhancer of zeste homolog 2 (EZH2), the catalytic part of the Polycomb repressive complex 2 (PRC2), has a prognostic role in renal cell carcinoma (RCC) and was recently shown to modulate the immune response by reducing tumor cell immunogenicity.

Methods

To investigate whether the prognostic role of EZH2 might be driven by a modified immune environment, more than 1800 RCCs were analyzed in a tissue microarray for EZH2 expression and CD8 positive lymphocytes were quantitated by automated digital imaging.

Results

EZH2 positivity was found in 75.2% of 1603 interpretable tumors. In clear cell RCC, high EZH2 expression was significantly linked to high ISUP, Furmann, and Thoenes grade (p < 0.0001 each), advanced stage (p < 0.0001), nodal (p = 0.0190) and distant metastasis (p < 0.0001) as well as shortened overall (p < 0.0027) and recurrence free survival (p < 0.0001). The density of CD8+ cells varied from 0 to 5048 cells/mm² (Median 120 cells/mm²). A high CD8+ count was significantly associated with high ISUP, Fuhrmann, and Thoenes grade (p < 0.0001 each), advanced tumor stage (p = 0.0041), distant metastasis (p = 0.0026) as well as reduced overall survival (p = 0.0373) and recurrence free survival (p = 0.0450). The density of CD8+ cells continuously increased with raising EZH2 levels (p < 0.0001).

Conclusion

Our data support a striking prognostic role of both EZH2 expression and the density of CD8+ cells in RCC. The tight relationship of EZH2 expression and CD8+ cell counts in RCC is consistent with models suggesting that EZH2 overexpression can be caused by high lymphocyte content in certain tumor types. Such a mechanism could explain the unique finding of high lymphocyte counts driving poor prognosis in RCC patients.

MUC1 oncoprotein mitigates ER stress via CDA-mediated reprogramming of pyrimidine metabolism

The Mucin 1 (MUC1) protein is overexpressed in various cancers and mediates chemotherapy resistance. However, the mechanism is not fully understood. Given that most chemotherapeutic drugs disrupt ER homeostasis as part of their toxicity, and MUC1 expression is regulated by proteins involved in ER homeostasis, we investigated the link between MUC1 and ER homeostasis. MUC1 knockdown in pancreatic cancer cells enhanced unfolded protein response (UPR) signaling and cell death upon ER stress induction. Transcriptomic analysis revealed alterations in the pyrimidine metabolic pathway and cytidine deaminase (CDA). ChIP and CDA activity assays showed that MUC1 occupied CDA gene promoter upon ER stress induction correlating with increased CDA expression and activity in MUC1-expressing cells as compared to MUC1 knockdown cells. Inhibition of either the CDA or pyrimidine metabolic pathway diminished survival in MUC1-expressing cancer cells upon ER stress induction. Metabolomic analysis demonstrated that MUC1-mediated CDA activity corresponded to deoxycytidine to deoxyuridine metabolic reprogramming upon ER stress induction. The resulting increase in deoxyuridine mitigated ER stress-induced cytotoxicity. Additionally, given 1) the established roles of MUC1 in protecting cells against reactive oxygen species (ROS) insults, 2) ER stress-generated ROS further promote ER stress and 3) the emerging anti-oxidant property of deoxyuridine, we further investigated if MUC1 regulated ER stress by a deoxyuridine-mediated modulation of ROS levels. We observed that deoxyuridine could abrogate ROS-induced ER stress to promote cancer cell survival. Taken together, our findings demonstrate a novel MUC1-CDA axis of the adaptive UPR that provides survival advantage upon ER stress induction.

MUC1-C regulates lineage plasticity driving progression to neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is an aggressive malignancy with no effective targeted therapies. The oncogenic MUC1-C protein is overexpressed in castration-resistant prostate cancer (CRPC) and NEPC, but its specific role is unknown. Here, we demonstrate that upregulation of MUC1-C in androgen-dependent PC cells suppresses androgen receptor (AR) axis signaling and induces the neural BRN2 transcription factor. MUC1-C activates a MYC→BRN2 pathway in association with induction of MYCN, EZH2 and NE differentiation markers (ASCL1, AURKA and SYP) linked to NEPC progression. Moreover, MUC1-C suppresses the p53 pathway, induces the Yamanaka pluripotency factors (OCT4, SOX2, KLF4 and MYC) and drives stemness. Targeting MUC1-C decreases PC self-renewal capacity and tumorigenicity, suggesting a potential therapeutic approach for CRPC and NEPC. In PC tissues, MUC1 expression associates with suppression of AR signaling and increases in BRN2 expression and NEPC score. These results highlight MUC1-C as a master effector of lineage plasticity driving progression to NEPC.

HO-1 promotes resistance to an EZH2 inhibitor through the pRB-E2F pathway: correlation with the progression of myelodysplastic syndrome into acute myeloid leukemia

Background

Myelodysplastic syndrome (MDS) can progress to acute myeloid leukemia (AML), and conventional chemotherapy (decitabine) does not effectively inhibit tumor cells. Enhancer of zeste homologue 2 (EZH2) and Heme oxygenase-1 (HO-1) are two key factors in patients resistance and deterioration.

Methods

In total, 58 MDS patients were divided into four groups. We analyzed the difference in HO-1 and EZH2 expression among the groups by real-time PCR. After treatment with Hemin or Znpp IX, flow cytometry was used to detect apoptosis and assess the cell cycle distribution of tumor cells. Following injection of mice with very high-risk MDS cells, spleen and bone marrow samples were studied by immunohistochemistry (IHC) and hematoxylin and eosin (H&E) staining. MDS cells overexpressing EZH2 and HO-1 were analyzed by high-throughput sequencing. The effect of HO-1 on the pRB-E2F pathway was analyzed by Western blotting. The effects of decitabine on P15INK4B and TP53 in MDS cells after inhibiting HO-1 were detected by Western blotting.

Results

Real-time PCR results showed that EZH2 and HO-1 expression levels were higher in MDS patients than in normal donors. The levels of HO-1 and EZH2 were simultaneously increased in the high-risk and very high-risk groups. Linear correlation analysis and laser scanning confocal microscopy results indicated that EZH2 was related to HO-1. MDS cells that highly expressed EZH2 and HO-1 infiltrated the tissues of experimental mice. IHC results indicated that these phenomena were related to the pRB-E2F pathway. High-throughput sequencing indicated that the progression of MDS to AML was related to EZH2. Using the E2F inhibitor HLM006474 and the EZH2 inhibitor JQEZ5, we showed that HO-1 could regulate EZH2 expression. HO-1 could stimulate the transcription and activation of EZH2 through the pRB-E2F pathway in MDS patients during chemotherapy, which reduced TP53 and P15INK4B expression.

Conclusions

EZH2 was associated with HO-1 in high-risk and very high-risk MDS patients. HO-1 could influence MDS resistance and progression to AML.

Use of immunotherapy in the treatment of gastric cancer

Gastric cancer (GC) is a malignant tumor that negatively impacts human health, which typically presents in the advanced stages of disease in the majority of patients. Despite the development of combination chemotherapy, only a modest survival advantage is gained in patients with GC treated by this method. Recently, cancer immunotherapies have received considerable attention as a viable therapeutic option for GC. Specifically, the immune checkpoint inhibitors, chimeric antigen rector (CAR)-T cells and tumor vaccines, represent immunotherapies that have exhibited promising effects in the treatment of GC. A number of clinical trials have employed either immuno-oncology monotherapies or combination therapies to improve the overall survival time (OS) and objective response rate (ORR) of patients with GC. The current review presents a summary of the clinical effects of checkpoint inhibitors, including CAR-T and tumor vaccines, in the treatment of GC.

MUC1-C Activates the NuRD Complex to Drive Dedifferentiation of Triple-Negative Breast Cancer Cells

The NuRD chromatin remodeling and deacetylation complex, which includes MTA1, MBD3, CHD4, and HDAC1 among other components, is of importance for development and cancer progression. The oncogenic mucin 1 (MUC1) C-terminal subunit (MUC1-C) protein activates EZH2 and BMI1 in the epigenetic reprogramming of triple-negative breast cancer (TNBC). However, there is no known link between MUC1-C and chromatin remodeling complexes. Here, we showed that MUC1-C binds directly to the MYC HLH-LZ domain and identified a previously unrecognized MUC1-C→MYC pathway that regulates the NuRD complex. MUC1-C/MYC complexes selectively activated the MTA1 and MBD3 genes and posttranscriptionally induced CHD4 expression in basal- but not luminal-type BC cells. In turn, MUC1-C formed complexes with these NuRD components on the ESR1 promoter. Downregulating MUC1-C decreased MTA1/MBD3/CHD4/HDAC1 occupancy and increased H3K27 acetylation on the ESR1 promoter, with induction of ESR1 expression and downstream estrogen response pathways. Targeting MUC1-C and these NuRD components also induced expression of FOXA1, GATA3, and other markers associated with the luminal phenotype. These findings support a model in which MUC1-C activates the NuRD complex to drive dedifferentiation and reprogramming of TNBC cells. SIGNIFICANCE: MUC1-C directly interacts with MYC to activate the NuRD complex, mediating regulation of the estrogen receptor in triple-negative breast cancer cells.

MUC1-C represses the RASSF1A tumor suppressor in human carcinoma cells

RASSF1A encodes a tumor suppressor that inhibits the RAS→RAF→MEK→ERK pathway and is one of the most frequently inactivated genes in human cancers. MUC1-C is an oncogenic effector of the cancer cell epigenome that is overexpressed in diverse carcinomas. We show here that MUC1-C represses RASSF1A expression in KRAS wild-type and mutant cancer cells. Mechanistically, MUC1-C occupies the RASSF1A promoter in a complex with the ZEB1 transcriptional repressor. In turn, MUC1-C/ZEB1 complexes recruit DNA methyltransferase 3b (DNMT3b) to the CpG island in the RASSF1A promoter. Targeting MUC1-C, ZEB1 and DNMT3b thereby decreases methylation of the CpG island and derepresses RASSF1A transcription. We also show that targeting MUC1-C regulates KRAS signaling, as evidenced by RNA-seq analysis, and decreases MEK/ERK activation, which is of importance for RAS-mediated tumorigenicity. These findings define a previously unrecognized role for MUC1-C in suppression of RASSF1A and support targeting MUC1-C as an approach for inhibiting MEK→ERK signaling.

Novel Apoptosis-Inducing Agents for the Treatment of Cancer, a New Arsenal in the Toolbox

Evasion from apoptosis is an important hallmark of cancer cells. Alterations of apoptosis pathways are especially critical as they confer resistance to conventional anti-cancer therapeutics, e.g., chemotherapy, radiotherapy, and targeted therapeutics. Thus, successful induction of apoptosis using novel therapeutics may be a key strategy for preventing recurrence and metastasis. Inhibitors of anti-apoptotic molecules and enhancers of pro-apoptotic molecules are being actively developed for hematologic malignancies and solid tumors in particular over the last decade. However, due to the complicated apoptosis process caused by a multifaceted connection with cross-talk pathways, protein–protein interaction, and diverse resistance mechanisms, drug development within the category has been extremely challenging. Careful design and development of clinical trials incorporating predictive biomarkers along with novel apoptosis-inducing agents based on rational combination strategies are needed to ensure the successful development of these molecules. Here, we review the landscape of currently available direct apoptosis-targeting agents in clinical development for cancer treatment and update the related biomarker advancement to detect and validate the efficacy of apoptosis-targeted therapies, along with strategies to combine them with other agents.

Targeting MUC1-C Inhibits TWIST1 Signaling in Triple-Negative Breast Cancer

The oncogenic MUC1-C protein and the TWIST1 epithelial-mesenchymal transition transcription factor (EMT-TF) are aberrantly expressed in triple-negative breast cancer (TNBC) cells. However, there is no known association between MUC1-C and TWIST1 in TNBC or other cancer cells. Here, we show that MUC1-C activates STAT3, and that MUC1-C and pSTAT3 drive induction of the TWIST1 gene. In turn, MUC1-C binds directly to TWIST1, and MUC1-C/TWIST1 complexes activate MUC1-C expression in an autoinductive circuit. The functional significance of the MUC1-C/TWIST1 circuit is supported by the demonstration that this pathway is sufficient for driving (i) the EMT-TFs, ZEB1 and SNAIL, (ii) multiple genes in the EMT program as determined by RNA-seq, and (iii) the capacity for cell invasion. We also demonstrate that the MUC1-C/TWIST1 circuit drives (i) expression of the stem cell markers SOX2, BMI1, ALDH1, and CD44, (ii) self-renewal capacity, and (iii) tumorigenicity. In concert with these results, we show that MUC1-C and TWIST1 also drive EMT and stemness in association with acquired paclitaxel (PTX) resistance. Of potential therapeutic importance, targeting MUC1-C and thereby TWIST1 reverses the PTX refractory phenotype as evidenced by synergistic activity with PTX against drug-resistant cells. These findings uncover a master role for MUC1-C in driving the induction of TWIST1, EMT, stemness, and drug resistance, and support MUC1-C as a highly attractive target for inhibiting TNBC plasticity and progression.

MUC1-C Integrates Chromatin Remodeling and PARP1 Activity in the DNA Damage Response of Triple-Negative Breast Cancer Cells

The oncogenic MUC1-C protein is overexpressed in triple-negative breast cancer (TNBC) cells and contributes to their epigenetic reprogramming and chemoresistance. Here we show that targeting MUC1-C genetically or pharmacologically with the GO-203 inhibitor, which blocks MUC1-C nuclear localization, induced DNA double-strand breaks and potentiated cisplatin (CDDP)-induced DNA damage and death. MUC1-C regulated nuclear localization of the polycomb group proteins BMI1 and EZH2, which formed complexes with PARP1 during the DNA damage response. Targeting MUC1-C downregulated BMI1-induced H2A ubiquitylation, EZH2-driven H3K27 trimethylation, and activation of PARP1. As a result, treatment with GO-203 synergistically sensitized both mutant and wild-type BRCA1 TNBC cells to the PARP inhibitor olaparib. These findings uncover a role for MUC1-C in the regulation of PARP1 and identify a therapeutic strategy for enhancing the effectiveness of PARP inhibitors against TNBC. SIGNIFICANCE: These findings demonstrate that targeting MUC1-C disrupts epigenetics of the PARP1 complex, inhibits PARP1 activity, and is synergistic with olaparib in TNBC cells.

Epigenetic silencing of the synthesis of immunosuppressive Siglec ligand glycans by NF-κB/EZH2/YY1 axis in early-stage colon cancers

Normal colonic epithelial cells express sialyl 6-sulfo Lewis^x and disialyl Lewis^a on their cell surface, which are ligands for the immunosuppressive molecule Siglec-7. Expression of these normal glycans is frequently lost upon malignant transformation by silencing DTDST and ST6GalNAc6 at the early stage of colorectal carcinogenesis, and leads to production of inflammatory mediators that facilitate carcinogenesis. Indeed, by querying The Cancer Genome Atlas datasets, we confirmed that the level of DTDST or ST6GalNAc6 mRNA is substantially decreased at the early stage of colorectal carcinogenesis. Cultured colon cancer cell lines were used in this study including DLD-1, HT-29, LS174T and SW620. Their promoter regions were strongly marked by repressive mark H3K27me3, catalyzed by EZH2 that was markedly upregulated in early stage of colorectal carcinogenesis. Suppression of EZH2 substantially downregulated H3K27me3 mark and upregulated DTDST and ST6GalNAc6 as well as expression of normal glycans and Siglec-binding activities. Transcription factor YY1 was vital for the recruitment of PRC2-containing EZH2 to both promoters. Inhibition of NF-κB substantially reduced EZH2 transcription and restored their mRNAs as well as the production of normal Siglec ligand glycans in the results obtained from in vitro studies on cultured colon cancer cell lines. These findings provide a putative mechanism for promotion of carcinogenesis by loss of immunosuppressive molecules by epigenetic silencing through NF-κB-mediated EZH2/YY1 axis.

EZH2 variants differentially regulate polycomb repressive complex 2 in histone methylation and cell differentiation

Background

Polycomb repressive complex 2 (PRC2) is responsible for establishing and maintaining histone H3K27 methylation during cell differentiation and proliferation. H3K27 can be mono-, di-, or trimethylated, resulting in differential gene regulation. However, it remains unknown how PRC2 specifies the degree and biological effects of H3K27 methylation within a given cellular context. One way to determine PRC2 specificity may be through alternative splicing of Ezh2, PRC2’s catalytic subunit, during cell differentiation and tissue maturation.

Results

We fully characterized the alternative splicing of Ezh2 in somatic cells and male germ cells and found that Ezh’s exon 14 was differentially regulated during mitosis and meiosis. The Ezh2 isoform containing exon 14 (ex14-Ezh2) is upregulated during cell cycle progression, consistent with a role in maintaining H3K27 methylation during chromatin replication. In contrast, the isoform lacking exon 14 (ex14D-Ezh2) was almost exclusively present in spermatocytes when new H3K27me2 is established during meiotic differentiation. Moreover, Ezh2’s transcript is normally controlled by E2F transcription activators, but in spermatocytes, Ezh2’s transcription is controlled by the meiotic regulator MYBL1. Compared to ex14-EZH2, ex14D-EZH2 has a diminished efficiency for catalyzing H3K27me3 and promotes embryonic stem cell differentiation.

Conclusions

Ezh2’s expression is regulated at transcriptional and post-transcriptional levels in a cellular context-dependent manner. EZH2 variants determine functional specificity of PRC2 in histone methylation during cell proliferation and differentiation.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0242-9) contains supplementary material, which is available to authorized users.

Targeting the human MUC1-C oncoprotein with an antibody-drug conjugate

Mucin 1 (MUC1) is a heterodimeric protein that is aberrantly overexpressed on the surface of diverse human carcinomas and is an attractive target for the development of mAb-based therapeutics. However, attempts at targeting the shed MUC1 N-terminal subunit have been unsuccessful. We report here the generation of mAb 3D1 against the nonshed oncogenic MUC1 C-terminal (MUC1-C) subunit. We show that mAb 3D1 binds with low nM affinity to the MUC1-C extracellular domain at the restricted α3 helix. mAb 3D1 reactivity is selective for MUC1-C-expressing human cancer cell lines and primary cancer cells. Internalization of mAb 3D1 into cancer cells further supported the conjugation of mAb 3D1 to monomethyl auristatin E (MMAE). The mAb 3D1-MMAE antibody-drug conjugate (ADC) (a) kills MUC1-C-positive cells in vitro, (b) is nontoxic in MUC1-transgenic (MUC1.Tg) mice, and (c) is active against human HCC827 lung tumor xenografts. Humanized mAb (humAb) 3D1 conjugated to MMAE also exhibited antitumor activity in (a) MUC1.Tg mice harboring syngeneic MC-38/MUC1 tumors, (b) nude mice bearing human ZR-75-1 breast tumors, and (c) NCG mice engrafted with a patient-derived triple-negative breast cancer. These findings and the absence of associated toxicities support clinical development of humAb 3D1-MMAE ADCs as a therapeutic for the many cancers with MUC1-C overexpression.

Targeting MUC1-C suppresses BCL2A1 in triple-negative breast cancer

B-cell lymphoma 2-related protein A1 (BCL2A1) is a member of the BCL-2 family of anti-apoptotic proteins that confers resistance to treatment with anti-cancer drugs; however, there are presently no agents that target BCL2A1. The MUC1-C oncoprotein is aberrantly expressed in triple-negative breast cancer (TNBC) cells, induces the epithelial-mesenchymal transition (EMT) and promotes anti-cancer drug resistance. The present study demonstrates that targeting MUC1-C genetically and pharmacologically in TNBC cells results in the downregulation of BCL2A1 expression. The results show that MUC1-C activates the BCL2A1 gene by an NF-κB p65-mediated mechanism, linking this pathway with the induction of EMT. The MCL-1 anti-apoptotic protein is also of importance for the survival of TNBC cells and is an attractive target for drug development. We found that inhibiting MCL-1 with the highly specific MS1 peptide results in the activation of the MUC1-C→NF-κB→BCL2A1 pathway. In addition, selection of TNBC cells for resistance to ABT-737, which inhibits BCL-2, BCL-xL and BCL-W but not MCL-1 or BCL2A1, is associated with the upregulation of MUC1-C and BCL2A1 expression. Targeting MUC1-C in ABT-737-resistant TNBC cells suppresses BCL2A1 and induces death, which is of potential therapeutic importance. These findings indicate that MUC1-C is a target for the treatment of TNBCs unresponsive to agents that inhibit anti-apoptotic members of the BCL-2 family.

Epigenetic Contribution of High-Mobility Group A Proteins to Stem Cell Properties

High-mobility group A (HMGA) proteins have been examined to understand their participation as structural epigenetic chromatin factors that confer stem-like properties to embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and cancer stem cells (CSCs). The function of HMGA was evaluated in conjunction with that of other epigenetic factors such as histones and microRNAs (miRs), taking into consideration the posttranscriptional modifications (PTMs) of histones (acetylation and methylation) and DNA methylation. HMGA proteins were coordinated or associated with histone and DNA modification and the expression of the factors related to pluripotency. CSCs showed remarkable differences compared with ESCs and iPSCs.

MUC1-C activates polycomb repressive complexes and downregulates tumor suppressor genes in human cancer cells

The PRC2 and PRC1 complexes are aberrantly expressed in human cancers and have been linked to decreases in patient survival. MUC1-C is an oncoprotein that is also overexpressed in diverse human cancers and is associated with a poor prognosis. Recent studies have supported a previously unreported function for MUC1-C in activating PRC2 and PRC1 in cancer cells. In the regulation of PRC2, MUC1-C (i) drives transcription of the EZH2 gene, (ii) binds directly to EZH2, and (iii) enhances occupancy of EZH2 on target gene promoters with an increase in H3K27 trimethylation. Regarding PRC1, which is recruited to PRC2 sites in the hierarchical model, MUC1-C induces BMI1 transcription, forms a complex with BMI1, and promotes H2A ubiquitylation. MUC1-C thereby contributes to the integration of PRC2 and PRC1-mediated repression of tumor suppressor genes, such as CDH1, CDKN2A, PTEN and BRCA1. Like PRC2 and PRC1, MUC1-C is associated with the epithelial-mesenchymal transition (EMT) program, cancer stem cell (CSC) state, and acquisition of anticancer drug resistance. In concert with these observations, targeting MUC1-C downregulates EZH2 and BMI1, inhibits EMT and the CSC state, and reverses drug resistance. These findings emphasize the significance of MUC1-C as a therapeutic target for inhibiting aberrant PRC function and reprogramming the epigenome in human cancers.

MUC1-C Induces PD-L1 and Immune Evasion in Triple-Negative Breast Cancer

The immune checkpoint ligand PD-L1 and the transmembrane mucin MUC1 are upregulated in triple-negative breast cancer (TNBC), where they contribute to its aggressive pathogenesis. Here, we report that genetic or pharmacological targeting of the oncogenic MUC1 subunit MUC1-C is sufficient to suppress PD-L1 expression in TNBC cells. Mechanistic investigations showed that MUC1-C acted to elevate PD-L1 transcription by recruitment of MYC and NF-κB p65 to the PD-L1 promoter. In an immunocompetent model of TNBC in which Eo771/MUC1-C cells were engrafted into MUC1 transgenic mice, we showed that targeting MUC1-C associated with PD-L1 suppression, increases in tumor-infiltrating CD8+ T cells and tumor cell killing. MUC1 expression in TNBCs also correlated inversely with CD8, CD69, and GZMB, and downregulation of these markers associated with decreased survival. Taken together, our findings show how MUC1 contributes to immune escape in TNBC, and they offer a rationale to target MUC1-C as a novel immunotherapeutic approach for TNBC treatment.Significance: These findings show how upregulation of the transmembrane mucin MUC1 contributes to immune escape in an aggressive form of breast cancer, with potential implications for a novel immunotherapeutic approach. Cancer Res; 78(1); 205-15. ©2017 AACR.