LH HCG-RECEPTOR IS COUPLED TO BOTH ADENYLATE-CYCLASE AND PROTEIN-KINASE-C SIGNALING PATHWAYS IN ISOLATED MOUSE LEYDIG-CELLS/

The aim of this study was to examine whether or not a protein kinase C -dependent pathway is involved in the desensitization process of the L H/hCG-receptor-linked adenylate cyclase system in isolated mouse Leydi g cells. Treatment of these cells with the phorbol ester, 4-beta-phorb ol 12-myristate 13-acetate (PMA) leads to a translocation (and a putat ive activation) of protein kinase C from the cytosol to the plasma mem brane, as evidenced by the Western blotting procedure using particulat e and cytosolic fractions of Percoll-purified mouse Leydig cells. A si milar translocation is also observed following the treatment of mouse Leydig cells with hCG. Data obtained show that this effect is time-dep endent and is mediated specifically through the LH/hCG-receptor. Furth ermore, we show that the treatment of Leydig cells with either PMA or hCG leads to a desensitization of the adenylate cyclase stimulated wit h hCG, hCG plus GppNHp or AlF4-. This desensitization was not accompan ied by a change in the [I-125]-hCG binding to membrane receptors. Thus we provide here direct evidence that hCG is capable of activating pro tein kinase C. In addition, we postulate that PMA as well as hCG-treat ment leads to a lesion located at a site distal to the receptor/G-prot ein interaction but proximal to the adenylate cyclase activation and t hat the translocation (and activation) of protein kinase C may be a co mmon mechanism involved in this desensitizing effect caused by both PM A and hCG on Leydig cells.