Protein kinase C inhibits cyclic adenosine monophosphate generation by histamine and truncated glucagon like peptide 1 in the human gastric cancer cell line HGT-1.

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Abstract
The HGT-1 gastric cancer cell line was used to determine the actions of protein kinase C on the stimulation of adenylate cyclase by the human histamine H2 receptor, and the receptors for gastric inhibitory polypeptide and truncated glucagon like peptide 1 (TGLP-1). Suspensions of HGT-1 cells were preincubated with the activator of protein kinase C, 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 nmol/l), for 10 minutes. The subsequent cyclic adenosine monophosphate (AMP) response to 0.5 mmol/l histamine or 100 nmol/l TGLP-1 was reduced by comparison with control cells preincubated in the absence of TPA. The cyclic AMP response to 100 nmol/l gastric inhibitory polypeptide was enhanced by preincubation with TPA, while the responses to cholera toxin and forskolin were unaffected. Preincubation with pertussis toxin prevented the enhancement of the gastric inhibitory polypeptide response by TPA, suggesting an involvement of an inhibitory guanine nucleotide regulatory subunit of the Gi class, but did not change the inhibition of histamine stimulation. In conclusion, activation of protein kinase C produces a specific inhibition of the effects of histamine and TGLP-1 on adenylate cyclase activity in a human gastric cancer cell line by acting at a site close to their receptors.