Nakanishi S, Catt K J, Balla T
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5317-21. doi: 10.1073/pnas.92.12.5317.
The synthesis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], the immediate precursor of intracellular signals generated by calcium-mobilizing hormones and growth factors, is initiated by the conversion of phosphatidylinositol to phosphatidylinositol 4-phosphate [PtdIns(4)P] by phosphatidylinositol 4-kinase (PtdIns 4-kinase). Although cells contain several PtdIns 4-kinases, the enzyme responsible for regulating the synthesis of hormone-sensitive PtdIns(4,5)P2 pools has not been identified. In this report we describe the inhibitory effect of micromolar concentrations of wortmannin (WT) on the synthesis of hormone-sensitive PtdIns(4)P and PtdIns(4,5)P2 pools in intact adrenal glomerulosa cells, and the presence of a WT-sensitive PtdIns 4-kinase in adrenocortical extracts. In addition to its sensitivity to the PtdIns 3-kinase inhibitor WT, this enzyme is distinguished from the recognized membrane-bound PtdIns 4-kinases by its molecular size and weak membrane association. Inhibition of this PtdIns 4-kinase by WT results in rapid loss of the hormone-sensitive PtdIns(4,5)P2 pool in angiotensin II-stimulated glomerulosa cells. Consequently, WT treatment inhibits the sustained but not the initial increases in inositol 1,4,5-trisphosphate and cytoplasmic [Ca2+] in a variety of agonist-stimulated cells, including adrenal glomerulosa cells, NIH 3T3 fibroblasts, and Jurkat lymphoblasts. These results indicate that a specific WT-sensitive PtdIns 4-kinase is critical for the maintenance of the agonist-sensitive polyphosphoinositide pool in several cell types.
磷脂酰肌醇4,5 - 二磷酸[PtdIns(4,5)P2]是由钙动员激素和生长因子产生的细胞内信号的直接前体，其合成起始于磷脂酰肌醇4 - 激酶（PtdIns 4 - 激酶）将磷脂酰肌醇转化为磷脂酰肌醇4 - 磷酸[PtdIns(4)P]。虽然细胞含有多种PtdIns 4 - 激酶，但负责调节激素敏感型PtdIns(4,5)P2池合成的酶尚未确定。在本报告中，我们描述了微摩尔浓度的渥曼青霉素（WT）对完整肾上腺球状带细胞中激素敏感型PtdIns(4)P和PtdIns(4,5)P2池合成的抑制作用，以及肾上腺皮质提取物中存在WT敏感的PtdIns 4 - 激酶。除了对PtdIns 3 - 激酶抑制剂WT敏感外，该酶在分子大小和弱膜结合方面与公认的膜结合PtdIns 4 - 激酶不同。WT对该PtdIns 4 - 激酶的抑制导致血管紧张素II刺激的球状带细胞中激素敏感型PtdIns(4,5)P2池迅速丧失。因此，WT处理抑制了多种激动剂刺激细胞（包括肾上腺球状带细胞、NIH 3T3成纤维细胞和Jurkat淋巴细胞）中肌醇1,4,5 - 三磷酸和细胞质[Ca2+]的持续增加，但不抑制其初始增加。这些结果表明，一种特定的WT敏感型PtdIns 4 - 激酶对于维持几种细胞类型中激动剂敏感的多磷酸肌醇池至关重要。
