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.