Condorelli G, Formisano P, Miele C, Beguinot F
Centro di Endocrinologia ed Oncologia Sperimentale del C.N.R., University of Naples, II Medical School, Italy.
Endocrinology. 1992 Mar;130(3):1615-25. doi: 10.1210/endo.130.3.1311244.
TSH regulation of insulin and insulin-like growth factor-I (IGF-I) receptor kinases has been studied in FRTL5 cultured thyroid cells. Preincubation of intact cells with TSH increased by 2-fold insulin and IGF-I receptor autophosphorylation and phosphorylation of the p175 endogenous substrate for the receptors. Enhanced phosphorylations reached a maximum within 30 min, were maintained for 30 min more, and vanished after 120 min of TSH incubation. TSH dose-responses exhibited half-maximal and maximal effects at 1 and 10 pM, respectively. In vitro, insulin as well as IGF-I receptors purified from cells treated with 10 pM TSH also exhibited 2-fold enhanced receptor autophosphorylation and kinase activity toward the exogenous substrate poly(Glu,Tyr) (4:1). At variance with TSH, cell incubation with either 8-bromo-cAMP or the protein kinase-C activator 12-O-tetradecanoylphorbol-13-acetate inhibited insulin and IGF-I receptor kinases. In intact cells, TSH stimulation of insulin and IGF-I receptor kinases was accompanied by enhanced turnover of phosphate on autophosphorylated receptors, increased receptor tyrosine phosphorylation, and decreased receptor serine/threonine phosphorylation in response to insulin. Incubation of in vivo labeled insulin and IGF-I receptors with extracts from TSH-treated cells also decreased receptor phosphoserine and phosphothreonine content. Furthermore, preincubation of insulin and IGF-I receptors with extracts from TSH-treated cells enhanced in vitro autophosphorylation. The latter effect was inhibited by the serine/threonine phosphatase inhibitors fluoride and okadaic acid, but not by the tyrosine phosphatase inhibitor vanadate. The data suggest that in FRTL5 cells, TSH induces the activity of a Ser/Thr protein phosphatase, which dephosphorylates insulin and IGF-I receptors and enhances their endogenous kinases.
在FRTL5培养的甲状腺细胞中，研究了促甲状腺激素（TSH）对胰岛素及胰岛素样生长因子-I（IGF-I）受体激酶的调节作用。完整细胞与TSH预孵育后，胰岛素和IGF-I受体的自身磷酸化以及受体的内源性底物p175的磷酸化增加了2倍。增强的磷酸化在30分钟内达到最大值，再持续30分钟，在TSH孵育120分钟后消失。TSH剂量反应分别在1和10 pM时表现出半最大效应和最大效应。在体外，从用10 pM TSH处理的细胞中纯化的胰岛素以及IGF-I受体，其自身磷酸化和对外源底物聚（Glu，Tyr）（4:1）的激酶活性也增强了2倍。与TSH不同，用8-溴-cAMP或蛋白激酶C激活剂12-O-十四烷酰佛波醇-13-乙酸酯孵育细胞会抑制胰岛素和IGF-I受体激酶。在完整细胞中，TSH刺激胰岛素和IGF-I受体激酶伴随着自身磷酸化受体上磷酸盐周转的增强、受体酪氨酸磷酸化的增加以及对胰岛素反应时受体丝氨酸/苏氨酸磷酸化的减少。用TSH处理的细胞提取物孵育体内标记的胰岛素和IGF-I受体，也会降低受体磷酸丝氨酸和磷酸苏氨酸的含量。此外，用TSH处理的细胞提取物对胰岛素和IGF-I受体进行预孵育可增强体外自身磷酸化。后一种效应被丝氨酸/苏氨酸磷酸酶抑制剂氟化物和冈田酸抑制，但不被酪氨酸磷酸酶抑制剂钒酸盐抑制。数据表明，在FRTL5细胞中，TSH诱导一种丝氨酸/苏氨酸蛋白磷酸酶的活性，该酶使胰岛素和IGF-I受体去磷酸化并增强其内源激酶活性。
