Induction of mucin gene expression in human colonic cell lines by PMA is dependent on PKC-epsilon

Treatment of HT-29 cells with phorbol 12-myristate 13-acetate (PMA), an act ivator of protein kinase C (PKC), induces MUC2 expression. To investigate t he role of PKC in regulating mucin genes in intestinal cells, we examined t he regulation of MUC1, MUC2, MUC5AC, MUC5B, and MUC6 expression in two huma n mucin-producing colonic cell lines, T84 and HT29/A1. T84 and HT29/A1 cell s (at 80-90% confluency) were exposed to 100 nM PMA for 0, 3, and 6 h. Twof old or greater increases in mRNA levels for MUC2 and MUC5AC were observed i n both cell lines during this time period, whereas the levels of MUC1, MUC5 B, and MUC6 mRNAs were only marginally affected. These results indicated th at PKC differentially regulates mucin gene expression and that it may be re sponsible for altered mucin expression. Our previous results suggested that the Ca2+-independent PKC-epsilon isoform appeared to mediate PMA-regulated mucin exocytosis in these cell lines. To determine if PKC-epsilon was also involved in MUC2/MUC5AC gene induction, HT29/A1 cells were stably transfec ted with either a wild-type PKC-epsilon or a dominant-negative ATP-binding mutant of PKC-epsilon (PKC-epsilon K437R). Overexpression of the dominant-n egative PKC-epsilon K437R blocked induction of both mucin genes, whereas PM A-induced mucin gene expression was not prevented by overexpression of wild -type PKC-epsilon. PMA-dependent MUC2 mucin secretion was also blocked in c ells overexpressing the dominant-negative PKC-epsilon K437R. On the basis o f these observations, PKC-epsilon appears to mediate the expression of two major gastrointestinal mucins in response to PMA as well as PMA-regulated m ucin exocytosis.