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 activator of protein kinase C (PKC), induces MUC2 expression. To investigate the role of PKC in regulating mucin genes in intestinal cells, we examined the regulation of MUC1, MUC2, MUC5AC, MUC5B, and MUC6 expression in two human mucin-producing colonic cell lines, T84 and HT29/A1. T84 and HT29/A1 cells (at 80-90% confluency) were exposed to 100 nM PMA for 0, 3, and 6 h. Twofold or greater increases in mRNA levels for MUC2 and MUC5AC were observed in both cell lines during this time period, whereas the levels of MUC1, MUC5B, and MUC6 mRNAs were only marginally affected. These results indicated that PKC differentially regulates mucin gene expression and that it may be responsible for altered mucin expression. Our previous results suggested that the Ca(2+)-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 transfected with either a wild-type PKC-epsilon or a dominant-negative ATP-binding mutant of PKC-epsilon (PKC-epsilon K437R). Overexpression of the dominant-negative PKC-epsilon K437R blocked induction of both mucin genes, whereas PMA-induced mucin gene expression was not prevented by overexpression of wild-type PKC-epsilon. PMA-dependent MUC2 mucin secretion was also blocked in cells overexpressing the dominant-negative PKC-epsilon K437R. On the basis of these observations, PKC-epsilon appears to mediate the expression of two major gastrointestinal mucins in response to PMA as well as PMA-regulated mucin exocytosis.