MUC1-C represses the RASSF1A tumor suppressor and activated Kras signaling in human carcinoma cells

RASSF1A encodes a tumor suppressor that inhibits RAS'RAF'MEK'ERK signaling 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 multiple types of 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 thus decreases methylation of the CpG island and derepresses RASSF1A transcription. We also show that targeting MUC1-C downregulates KRAS signaling with decreases in 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 KRAS signaling. Overall design: Using Lentiviral vector, a control shRNA hairpin and shRNA against MUC1-C were used to generate the stably silenced MUC1-C and control cell lines of BT-549 and A549 cells respectively. Total RNA were isolated from 3 different sets of control shRNA and MUC1-shRNA for both BT549 and A549 cell types and used for RNA-seq library preparation.