Protein kinase C activity in human thyroid carcinoma and adenoma.

Protein kinase C (PKC) activity was examined in the cytosolic and particulate fractions of homogenates obtained from 12 papillary thyroid carcinomas, 12 follicular thyroid adenomas, and the adjacent normal thyroid tissue. Particulate PKC activity was elevated significantly in thyroid carcinomas compared with normal thyroid tissue (P < 0.01) and adenomas (P < 0.05). By contrast, cytosolic PKC activity of carcinomas and adenomas was lower significantly than that of normal thyroid tissue (P < 0.01). The percentage of particulate PKC activity in carcinoma and adenoma was higher than in normal thyroid tissue (carcinoma, P < 0.001; adenoma, P < 0.01). The average particulate PKC activity of carcinomas more than 3 cm in diameter was significantly lower than that of carcinomas less than or equal to 3 cm in diameter (P < 0.05). The average cytosolic PKC activity of carcinomas more than 3 cm also was lower significantly than that of smaller carcinomas (P < 0.05). These results suggest that alterations in PKC activity may be important in the development of papillary thyroid cancer.