Role of tyrosine kinases in gastrin induction of ornithine decarboxylase in colonic mucosa.
An organ culture system was utilized to evaluate the role of tyrosine kinases (Tyr-k) and tyrosine-specific phosphorylation of proteins in gastrin regulation of ornithine decarboxylase (ODC) activity in colonic mucosa. Exposure of colonic mucosal explants to gastrin (50-100 ng G-17 I/ml) resulted in a profound stimulation of both Tyr-k and ODC activities compared with the corresponding basal levels. Whereas the maximal stimulation (ranging between 70 and 150%) of Tyr-k occurred within 10-15 min of exposure to gastrin, ODC activity was significantly stimulated (180%) 2 h after exposure to the hormone, and at 4 h it was found to be 750% above the corresponding basal level. Difluoromethylornithine (DFMO; 2 mM), an irreversible inhibitor of ODC, completely abolished the gastrin-mediated stimulation of ODC but not Tyr-k activity. On the other hand, genistein (100 micrograms/ml), a specific inhibitor of Tyr-k, caused a total suppression of the gastrin-induced stimulation of both Tyr-k and ODC. Gastrin also stimulated tyrosyl phosphorylation of a colonic mucosal membrane protein with molecular mass of 57 kDa, and genistein greatly attenuated this effect. We conclude that gastrin stimulates colonic mucosal ODC in vitro, and Tyr-k may be required for the regulation of this process.
Majumdar
A P
AP
Research Service, Veterans Administration Medical Center, Allen Park, Michigan 48101.
D000818:Animals; D003106:Colon / Q000201:enzymology; D000518:Eflornithine / Q000494:pharmacology; D004790:Enzyme Induction; D005755:Gastrins / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D009924:Organ Culture Techniques; D009955:Ornithine Decarboxylase / Q000096:biosynthesis*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344
D005755:Gastrins; D011505:Protein-Tyrosine Kinases; D009955:Ornithine Decarboxylase; D000518:Eflornithine