Epigenetic regulation (DNA methylation, histone modifications) of the 11p15 mucin genes (MUC2, MUC5AC, MUC5B, MUC6) in epithelial cancer cells.

The human genes MUC2, MUC5AC, MUC5B and MUC6 are clustered on chromosome 11 and encode large secreted gel-forming mucins. The frequent occurrence of their silencing in cancers and the GC-rich structure of their promoters led us to study the influence of epigenetics on their expression. Pre- and post-confluent cells were treated with demethylating agent 5-aza-2'-deoxycytidine and histone deacetylase (HDAC) inhibitor, trichostatin A. Mapping of methylated cytosines was performed by bisulfite-treated genomic DNA sequencing. Histone modification status at the promoters was assessed by chromatin immunoprecipitation assays. Our results indicate that MUC2 was regulated by site-specific DNA methylation associated with establishment of a repressive histone code, whereas hypermethylation of MUC5B promoter was the major mechanism responsible for its silencing. DNA methyltransferase 1 was identified by small interfering RNA approach as a regulator of MUC2 and MUC5B endogenous expression that was potentiated by HDAC2. MUC2 and MUC5B epigenetic regulation was cell-specific, depended on cell differentiation status and inhibited their activation by Sp1. The expression of MUC5AC was rarely influenced by epigenetic mechanisms and methylation of MUC6 promoter was not correlated to its silencing. In conclusion, this study demonstrates the important role for methylation and/or histone modifications in regulating the 11p15 mucin genes in epithelial cancer cells.