Brostrom M A, Brostrom C O, Bocckino S B, Green S S
J Cell Physiol. 1984 Nov;121(2):391-401. doi: 10.1002/jcp.1041210217.
Effects of Ca2+ and hormones on short-term protein synthesis were examined utilizing intact Ca2+-depleted and Ca2+-restored GH3 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 Ca2+. Thyrotropin-releasing hormone (TRH) rapidly enhanced amino acid incorporation and prolactin production, with both effects being reserved by EGTA in excess of extracellular Ca2+ or prevented by cellular Ca2+ 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 Ca2+-restored than in Ca2+-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 Ca2+ 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 Ca2+ 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 Ca2+ of amino acid incorporation and prolactin production. Unlike total prolactin, the total protein content of GH3 cells during these short incubations was not altered by Ca2+, hormones or trifluoperazine. It is proposed that hormones and Ca2+, which have been demonstrated to regulate prolactin secretion and prolactin mRNA transcription in GH3 cells, also exert translational controls which serve to facilitate the overall expression of the prolactin gene.
利用完整的缺钙和再补钙的GH3垂体肿瘤细胞作为模型系统，研究了Ca2+和激素对短期蛋白质合成的影响。在短期孵育期间，完全生长培养基中的细胞氨基酸掺入量被超过Ca2+浓度的EGTA显著降低。促甲状腺激素释放激素（TRH）迅速增强氨基酸掺入和催乳素产生，这两种作用都被超过细胞外Ca2+的EGTA所抑制或被细胞缺钙所阻止。表皮生长因子和佛波酯肉豆蔻酸酯（PMA）也刺激氨基酸掺入和催乳素产生；这些试剂在再补钙制剂中提供的蛋白质合成绝对增加量显著大于缺钙制剂。提高催乳素产生的TRH和PMA浓度与增加氨基酸掺入总蛋白质速率的浓度相同。氨基酸掺入和催乳素产生的细胞外Ca2+浓度依赖性相似，且不受激素影响。PMA是测试试剂中最有效的，Ca2+促进氨基酸掺入相同的蛋白质谱。激素对蛋白质合成的刺激并非归因于氨基酸摄取、附着于底物、激素结合、蛋白质分解代谢或转录的改变。三氟拉嗪选择性地阻止Ca2+对氨基酸掺入和催乳素产生的刺激。与总催乳素不同，在这些短期孵育期间，GH3细胞的总蛋白质含量不受Ca2+、激素或三氟拉嗪的影响。有人提出，已证明在GH3细胞中调节催乳素分泌和催乳素mRNA转录的激素和Ca2+，也发挥翻译控制作用，以促进催乳素基因的整体表达。
