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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 LH/hCG-receptor-linked adenylate cyclase system in isolated mouse Leydig cells. Treatment of these cells with the phorbol ester, 4-β-phorbol 12-myristate 13-acetate (PMA) leads to a translocation (and a putative activation) of protein kinase C from the cytosol to the plasma membrane, as evidenced by the Western blotting procedure using particulate and cytosolic fractions of Percoll-purified mouse Leydig cells. A similar translocation is also observed following the treatment of mouse Leydig cells with hCG. Data obtained show that this effect is time-dependent and is mediated specifically through the LH/hCG-receptor. Furthermore, we show that the treatment of Leydig cells with either PMA or hCG leads to a desensitization of the adenylate cyclase stimulated with hCG, hCG plus GppNHp or AIF (4) (-) . This desensitization was not accompanied by a change in the [(125)I]-hCG binding to membrane receptors. Thus we provide here direct evidence that hCG is capable of activating protein kinase C. In addition, we postulate that PMA as well as hCG-treatment leads to a lesion located at a site distal to the receptor/G-protein interaction but proximal to the adenylate cyclase activation and that the translocation (and activation) of protein kinase C may be a common mechanism involved in this desensitizing effect caused by both PMA and hCG on Leydig cells. |
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