Theα isoform of protein kinase C inhibits histamine-stimulated adenylate cyclase activity in a particulate fraction of the human gastric cancer cell line HGT-1

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Abstract
The isoform of protein kinase C responsible for the inhibition of histamine-stimulated adenylate cyclase by the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA), has been investigated in a particulate fraction prepared from the human gastric cancer cell line HGT-1. Theα and∈ isoforms of protein kinase C were detected in HGT-1 cells and in a 40,000 × g particulate fraction by immunoblotting procedures. The inhibitory effect of TPA on histamine-stimulated adenylate cyclase was enhanced by the presence of Ca2+, but decreased in a concentrationdependent manner by anti-peptide antibody to protein kinase Cα, but not to protein kinase C∈. Addition of Ca2+ and TPA to the 40,000 × g particulate fraction stimulated the phosphorylation of the protein kinase C substrate myelin basic peptide 4–14. Protein kinase Cα is probably the isoform responsible for inhibition of histamine-stimulated adenylate cyclase in HGT-1 cells.