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Bile acids, non‐phorbol‐ester‐type tumor promoters, stimulate the phosphorylation of protein kinase C substrates in human platelets and colon cell line HT29
Author(s) -
Huang X. P.,
Fan X. T.,
Desjeux J. F.,
Castagna M.
Publication year - 1992
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910520319
Subject(s) - protein kinase c , diacylglycerol kinase , phosphatidylserine , biochemistry , phospholipid , egta , phosphorylation , platelet activation , phorbol , tetradecanoylphorbol acetate , enzyme , chemistry , enzyme activator , biology , platelet , microbiology and biotechnology , calcium , immunology , organic chemistry , membrane
Protein kinase C (PKC) is the target for a number of tumor promoters. The mechanism underlying the promoting effects of bile acids in colorectal cancer is not understood. We report that sodium deoxycholate (DOC) triggered activation of PKC in physiological conditions. The biphasic effects of DOC upon PKC activation were Ca 2+ ‐stimulated and did not require phosphatidylserine (PtdSer) as phospholipid co‐factor. The optimal rate of activation was obtained at 0.4 mM DOC and reached approximately half the maximal rate of activation obtained in the presence of PtdSer. Similarly to PtdSer, DOC supported diacylglycerol‐as well as phorbol‐ester‐mediated PKC activation. The reciprocal effects of PtdSer and DOC upon PKC in either 0.5 mM CaCl 2 or 0.5 mM EGTA suggest that DOC interacts with the phospholipid‐binding domain to elicit PKC activation. DOC‐supported enzyme activation exhibited substrate specificity different from that of PtdSer‐supported enzyme activation. All tested primary and secondary bile acids activated PKC to various extents, with DOC being the most potent. We suggest that amphipathic bile acids acting in a PtdSer‐like manner provide the hydrophobic environment required for PKC activation. Treatment of 32 P‐labeled platelets and colonic cells HT29 C1. 19A with DOC enhanced the phosphorylation of endogenous substrates for PKC. Colonic cells responsive at 50 μM DOC, appeared to be 10‐fold more sensitive than platelets. We suggest that direct or indirect activation of PKC by bile acids may account for the promoting effects of these non‐phorbol‐ester‐type tumor promoters. © 1992 Wiley‐Liss, Inc.