TSH REGULATION OF THYROIDAL PROTEIN-KINASE-C ISOENZYMES

Protein Kinase C (PKC) isoenzymes differ in their tissue expression, r equirements for activation and cellular localisation, which suggests t hey have discrete functions in cell signalling. We have examined PKC i soenzymes present in sheep thyroid cells treated with varying concentr ations of TSH to induce differentiation. Differentiated function was a ssessed by measurements of thyroid hormone production. Thyroid hormone production was dependent on TSH and was maximal at 0.3 nM TSH (300 mu U per ml). Higher TSH levels decreased production of both thyroid hor mones. Western blotting of cell extracts using specific antisera to PK C isoenzymes and confocal microscopy of immunostained cells, showed th at undifferentiated cells grown in the absence of TSH contained alpha, delta and zeta as the major PKC isoenzymes. They contained very low l evels of PKC-beta and PKC-8. Upon stimulation with 0.3 nM TSH, PKC-del ta immunoreactivity fell to an almost undetectable level. At high TSH concentrations (10 nM, 10 mU per ml) PKC-delta returned to control lev els. Conversely the beta and epsilon isoenzymes showed a marked increa se at 0.1-0.3 nM TSH with a decrease to control levels at 10 nM TSH. B oth the alpha and zeta isoenzymes showed a gradual increase in express ion with TSH treatment, which did not decrease at the higher TSH conce ntrations. The subcellular distribution of the isoenzymes was also reg ulated by TSH. These data show the marked regulation of the synthesis of PKC isoenzymes in thyroid cells in undifferentiated, fully differen tiated and partially differentiated thyroid cells. The role of the act ivation of these PKC isoenzymes remains to be determined.