Premium
Ca 2+ and hormones interact synergistically to stimulate rapidly both prolactin production and overall protein synthesis in pituitary tumor cells
Author(s) -
Brostrom Margaret A.,
Brostrom Charles O.,
Bocckino Stephen B.,
Green Susan S.
Publication year - 1984
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041210217
Subject(s) - prolactin , egta , extracellular , amino acid , trifluoperazine , stimulation , hormone , medicine , protein biosynthesis , thyrotropin releasing hormone , endocrinology , chemistry , biochemistry , biology , calmodulin , calcium , enzyme
Effects of Ca 2+ and hormones on short‐term protein synthesis were examined utilizing intact Ca 2+ ‐depleted and Ca 2+ ‐restored GH 3 pituitary tumor cells as a model system. Amino acid incorporation by cells in complete growth medium during short incubations was markedly reduced by EGTA concentrations in excess of Ca 2+ . Thyrotropin‐releasing hormone (TRH) rapidly enhanced amino acid incorporation and prolactin production, with both effects being reserved by EGTA in excess of extracellular Ca 2+ or prevented by cellular Ca 2+ depletion. Epidermal growth factor and phorbol myristate acetate (PMA) also stimulated amino acid incorporation and prolactin production; absolute increases in protein synthesis provided by these agents were significantly greater in Ca 2+ ‐restored than in Ca 2+ ‐depleted preparations. TRH and PMA concentrations which raised prolactin production were identical to those increasing the rate of amino acid incorporation into overall protein. The extracellular Ca 2+ concentration dependencies of amino acid incorporation and prolactin production were similar and were unchanged by hormone. PMA, the most efficacious of the agents tested, and Ca 2+ promoted incorporation of amino acid into the same spectrum of proteins. Stimulation of protein synthesis by hormones was not attributable to alterations in amino acid uptake, attachment to substrata, hormone binding, protein catabolism or transcription. Trifluoperazine selectively prevented the stimulation by Ca 2+ of amino acid incorporation and prolactin production. Unlike total prolactin, the total protein content of GH 3 cells during these short incubations was not altered by Ca 2+ , hormones or trifluoperazine. It is proposed that hormones and Ca 2+ , which have been demonstrated to regulate prolactin secretion and prolactin mRNA transcription in GH 3 cells, also exert translational controls which serve to facilitate the overall expression of the prolactin gene.