Takazawa K, Go M, Endo T, Erneux C, Onaya T
Third Department of Internal Medicine, University of Yamanashi Medical School, Japan.
J Endocrinol. 1995 Mar;144(3):527-32. doi: 10.1677/joe.0.1440527.
Inositol 1,4,5-trisphosphate (InsP3) 3-kinase phosphorylates the Ca(2+)-mobilizing second messenger InsP3 to inositol 1,3,4,5-tetrakisphosphate (InsP4). InsP3 5-phosphatase dephosphorylates InsP3 to inositol 1,4-bisphosphate (InsP2). We compared the effects of TSH added to a culture of FRTL-5 thyroid cells on the activity of InsP3 5-phosphatase and InsP3 3-kinase. InsP3 3-kinase activity was decreased at a physiological concentration of TSH. Inhibition of this activity started after 3 h of incubation with TSH and was maximal after 24 h. In contrast, InsP3 5-phosphatase activity was not affected by TSH under the same conditions. The inhibitory effect of TSH on InsP3 3-kinase was characterized as follows: a) inhibition of activity was mimicked by both dibutyryl cyclic AMP and forskolin; b) activity obtained by mixing lysates of TSH-stimulated and non-stimulated cells was the sum of each activity measured separately; c) inhibition persisted after a crude lysate of TSH-stimulated cells had been subjected to SDS/polyacrylamide gel electrophoresis and the extraction of InsP3 3-kinase activity. The data suggest that TSH reduced the activity of InsP3 3-kinase in FRTL-5 cells either by a phosphorylation/dephosphorylation mechanism, or by affecting expression of the enzyme.
肌醇1,4,5-三磷酸（InsP3）3-激酶将可动员钙离子的第二信使InsP3磷酸化为肌醇1,3,4,5-四磷酸（InsP4）。InsP3 5-磷酸酶将InsP3去磷酸化为肌醇1,4-二磷酸（InsP2）。我们比较了添加到FRTL-5甲状腺细胞培养物中的促甲状腺激素（TSH）对InsP3 5-磷酸酶和InsP3 3-激酶活性的影响。在生理浓度的TSH作用下，InsP3 3-激酶活性降低。与TSH孵育3小时后，该活性开始受到抑制，24小时后达到最大抑制。相比之下，在相同条件下，InsP3 5-磷酸酶活性不受TSH影响。TSH对InsP3 3-激酶的抑制作用具有以下特点：a）二丁酰环磷腺苷和福斯可林均可模拟其对活性的抑制作用；b）将TSH刺激的细胞裂解物与未刺激的细胞裂解物混合后测得的活性，是分别测量的每种活性之和；c）将TSH刺激的细胞粗裂解物进行SDS/聚丙烯酰胺凝胶电泳并提取InsP3 3-激酶活性后，抑制作用仍然存在。这些数据表明，TSH通过磷酸化/去磷酸化机制或通过影响该酶的表达来降低FRTL-5细胞中InsP3 3-激酶的活性。
