Calcium-activated, phospholipid-dependent protein kinase in human gastric mucosa and carcinoma

Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) activities in human gastric mucosa and carcinoma were examined. The bulk of protein kinase C activity was associated with the cytosol in both gastric mucosa and carcinoma. Protein kinase C activity in the soluble fraction in human gastric carcinoma was significantly higher than that in nonneoplastic gastric mucosa (P less than 0.05), the values being 357.7 and 215.3 units/g protein, respectively. On the other hand, cAMP-dependent protein kinase (protein kinase A) activity was decreased slightly in gastric carcinomas. The ratios of protein kinase C to protein kinase A in human gastric carcinoma and nonneoplastic mucosa were 0.849 and 0.435, respectively, the difference being significant (P less than 0.01). In DEAE-cellulose column chromatography, the elution profiles of protein kinases from gastric carcinomas were the same as those from gastric mucosas except that a larger peak of protein kinase C was found. It seems probable that increased protein kinase C activity plays an important role in the growth of human gastric carcinoma as a signal transducer.