Nonsteroidal antiestrogen inhibition of protein kinase C in human corpus luteum and placenta.
These studies were undertaken to determine whether nonsteroidal antiestrogens would inhibit the calcium/lipid-dependent protein kinase (protein kinase C) activity in hormonally-responsive human reproductive tissues. Cytosol was prepared from human corpus luteum and term placenta. Protein kinase C activity was examined with various antiestrogens, estrogens, and catecholestrogens. The nonsteroidal antiestrogens tamoxifen, clomiphene and Z-4-hydroxytamoxifen inhibited protein kinase C in cytosol from human corpora lutea and placentae in a concentration-dependent manner. The IC50 values were 35-45 microM for tamoxifen, 58-66 microM for clomiphene, and 88 microM for hydroxytamoxifen. Protein kinase C purified 600-fold from human placenta was also inhibited by tamoxifen. The estrogens, estradiol and diethylstilbestrol (DES), and the catecholestrogens, 2-hydroxyestradiol and 4-hydroxyestradiol, had no effect on protein kinase C activity, nor were they able to prevent the inhibition of protein kinase C by the antiestrogens. Inhibition of the enzyme by the antiestrogens was competitive with phosphatidylserine and 1,2-diolein. In addition, tamoxifen inhibited enzyme activity stimulated by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). The data suggest that the action of these antiestrogens on protein kinase C was a direct inhibition of the enzyme. Furthermore, the site of interaction showed markedly different structural specificity from that of the estrogen receptor.
Eyster
K M
KM
Department of Obstetrics and Gynecology, University of North Carolina School of Medicine, Chapel Hill 27599.
Clark
M R
MR
D003338:Corpus Luteum / Q000201:enzymology*; D004054:Diethylstilbestrol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D010920:Placenta / Q000201:enzymology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D013629:Tamoxifen / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004965:Estrogen Antagonists; D013629:Tamoxifen; D004054:Diethylstilbestrol; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate