Effects of Phorbol Esters on Protein Phosphorylation and Free T₃ Release by Mouse Thyroid Lobes

Abstract

Phospholipid-dependent calcium-activated protein kinase, previously identified and termed protein kinase C (1), is known to be widely distributed among various tissues. Although many proteins can be substrates of protein kinase C, little is known about its physiological role. Diacylglycerol, a major degradative product of phosphatidylinositol (PI) turnover, was reported to stimulate protein kinase C in vitro (2). Previously, Igarashi and Kondo (3) have clearly shown that a transient increase of diacylglcerol is elicited by TSH in hog thyroid follicles. We, therefore, wished to know whether thyroid protein kinase C has a role in thyroid physiology. In the present paper, we report some aspects of protein kinase C in mouse thyroid lobes.