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      Effect of tamoxifen, a nonsteroidal antiestrogen, on phospholipid/calcium-dependent protein kinase and phosphorylation of its endogenous substrate proteins from the rat brain and ovary

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      Biochemical Pharmacology

      Elsevier BV

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          Abstract

          Antiestrogens (tamoxifen, clomiphene and nafoxidine) were found to inhibit phospholipid/Ca2+-dependent protein kinase (PL/Ca-PK, or protein kinase C), whereas estrogens (estradiol and diethylstilbesterol) and the weakly estrogenic chlorotrianisene were inactive. Kinetic analysis indicated that the antiestrogens inhibited PL/Ca-PK competitively with respect to phosphatidylserine (Ki = 16-27 microM), but non-competitively with Ca2+ (Ki = 14-30 microM). Tamoxifen, but not diethylstilbesterol, also inhibited the phospholipid/Ca2+-dependent phosphorylation of various endogenous proteins from the total, solubilized fraction of the rat brain and ovary. Myosin light chain kinase, a calmodulin/Ca2+-dependent class of protein kinase, was similarly inhibited by tamoxifen; the drug, however, was without effect on cyclic AMP-dependent and cyclic GMP-dependent protein kinases. It is suggested that PL/Ca-PK, by virtue of the hydrophobic interactions required for the enzyme activation, may represent a potential site of action for the lipophilic antiestrogens, in addition to the commonly recognized intracellular estrogen receptors.

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          Author and article information

          Journal
          Biochemical Pharmacology
          Biochemical Pharmacology
          Elsevier BV
          00062952
          October 1985
          October 1985
          : 34
          : 20
          : 3649-3653
          Article
          10.1016/0006-2952(85)90225-4
          3840375
          © 1985

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