ABSTRACT
Immunotherapeutic approaches, particularly programmed death 1/programmed death ligand 1 (PD-1/PD-L1) blockade, have improved the treatment of non-small-cell lung cancer (NSCLC), supporting the premise that evasion of immune destruction is of importance for NSCLC progression. However, the signals responsible for upregulation of PD-L1 in NSCLC cells and whether they are integrated with the regulation of other immune-related genes are not known. Mucin 1 (MUC1) is aberrantly overexpressed in NSCLC, activates the nuclear factor-κB (NF-κB) p65âï¸ZEB1 pathway and confers a poor prognosis. The present studies demonstrate that MUC1-C activates PD-L1 expression in NSCLC cells. We show that MUC1-C increases NF-κB p65 occupancy on the CD274/PD-L1 promoter and thereby drives CD274 transcription. Moreover, we demonstrate that MUC1-C-induced activation of NF-κBâï¸ZEB1 signaling represses the TLR9 (toll-like receptor 9), IFNG, MCP-1 (monocyte chemoattractant protein-1) and GM-CSF genes, and that this signature is associated with decreases in overall survival. In concert with these results, targeting MUC1-C in NSCLC tumors suppresses PD-L1 and induces these effectors of innate and adaptive immunity. These findings support a previously unrecognized central role for MUC1-C in integrating PD-L1 activation with suppression of immune effectors and poor clinical outcome.
Subject(s)
B7-H1 Antigen/genetics , Carcinoma, Non-Small-Cell Lung , Immunity, Cellular/genetics , Lung Neoplasms , Mucin-1/physiology , Tumor Escape/genetics , A549 Cells , Animals , Carcinoma, Non-Small-Cell Lung/genetics , Carcinoma, Non-Small-Cell Lung/immunology , Carcinoma, Non-Small-Cell Lung/pathology , Cell Line, Tumor , Female , Gene Expression Regulation, Neoplastic , Humans , Lung Neoplasms/genetics , Lung Neoplasms/immunology , Lung Neoplasms/pathology , Mice , Mice, Nude , Signal Transduction/genetics , Signal Transduction/immunologyABSTRACT
B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1) is a component of the polycomb repressive complex 1 (PRC1) complex that is overexpressed in breast and other cancers, and promotes self-renewal of cancer stem-like cells. The oncogenic mucin 1 (MUC1) C-terminal (MUC1-C) subunit is similarly overexpressed in human carcinoma cells and has been linked to their self-renewal. There is no known relationship between MUC1-C and BMI1 in cancer. The present studies demonstrate that MUC1-C drives BMI1 transcription by a MYC-dependent mechanism in breast and other cancer cells. In addition, we show that MUC1-C blocks miR-200c-mediated downregulation of BMI1 expression. The functional significance of this MUC1-Câï¸BMI1 pathway is supported by the demonstration that targeting MUC1-C suppresses BMI1-induced ubiquitylation of H2A and thereby derepresses homeobox HOXC5 and HOXC13 gene expression. Notably, our results further show that MUC1-C binds directly to BMI1 and promotes occupancy of BMI1 on the CDKN2A promoter. In concert with BMI1-induced repression of the p16INK4a tumor suppressor, we found that targeting MUC1-C is associated with induction of p16INK4a expression. In support of these results, analysis of three gene expresssion data sets demonstrated highly significant correlations between MUC1-C and BMI1 in breast cancers. These findings uncover a previously unrecognized role for MUC1-C in driving BMI1 expression and in directly interacting with this stem cell factor, linking MUC1-C with function of the PRC1 in epigenetic gene silencing.
Subject(s)
Mucin-1/metabolism , Neoplasms/metabolism , Polycomb Repressive Complex 1/metabolism , Amino Acid Motifs , Amino Acid Sequence , Cell Line, Tumor , Cyclin-Dependent Kinase Inhibitor p16/genetics , Cyclin-Dependent Kinase Inhibitor p16/metabolism , Gene Expression Regulation, Neoplastic , Gene Silencing , Histones/metabolism , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Humans , Mucin-1/chemistry , Mucin-1/genetics , NF-kappa B/metabolism , Neoplasms/genetics , Promoter Regions, Genetic , Protein Binding , Protein Interaction Domains and Motifs , Proto-Oncogene Proteins c-myc/metabolism , Transcription, Genetic , UbiquitinationABSTRACT
Aberrant expression of the DNA methyltransferases (DNMTs) and disruption of DNA methylation patterns are associated with carcinogenesis and cancer cell survival. The oncogenic MUC1-C protein is aberrantly overexpressed in diverse carcinomas; however, there is no known link between MUC1-C and DNA methylation. Our results demonstrate that MUC1-C induces the expression of DNMT1 and DNMT3b, but not DNMT3a, in breast and other carcinoma cell types. We show that MUC1-C occupies the DNMT1 and DNMT3b promoters in complexes with NF-κB p65 and drives DNMT1 and DNMT3b transcription. In this way, MUC1-C controls global DNA methylation as determined by analysis of LINE-1 repeat elements. The results further demonstrate that targeting MUC1-C downregulates DNA methylation of the CDH1 tumor suppressor gene in association with induction of E-cadherin expression. These findings provide compelling evidence that MUC1-C is of functional importance to induction of DNMT1 and DNMT3b and, in turn, changes in DNA methylation patterns in cancer cells.
