Park S J, Itoh T, Takenawa T
Department of Biochemistry, Institute of Medical Science, University of Tokyo, Shirokanedai, Minato-ku, Tokyo 108, Japan.
J Biol Chem. 2001 Feb 16;276(7):4781-7. doi: 10.1074/jbc.M010177200. Epub 2000 Nov 21.
Phosphatidylinositol 4-phosphate 5-kinase (PIPK) catalyzes a final step in the synthesis of phosphatidylinositol 4,5-bisphosphate (PIP(2)), a lipid signaling molecule. Strict regulation of PIPK activity is thought to be essential in intact cells. Here we show that type I enzymes of PIPK (PIPKI) are phosphorylated by cyclic AMP-dependent protein kinase (PKA), and phosphorylation of PIPKI suppresses its activity. Serine 214 was found to be a major phosphorylation site of PIPK type Ialpha (PIPKIalpha) that is catalyzed by PKA. In contrast, lysophosphatidic acid-induced protein kinase C activation increased PIPKIalpha activity. Activation of PIPKIalpha was induced by dephosphorylation, which was catalyzed by an okadaic acid-sensitive phosphatase, protein phosphatase 1 (PP1). In vitro dephosphorylation of PIPKIalpha with PP1 increased PIPK activity, indicating that PP1 plays a role in lysophosphatidic acid-induced dephosphorylation of PIPKIalpha. These results strongly suggest that activity of PIPKIalpha in NIH 3T3 cells is regulated by the reversible balance between PKA-dependent phosphorylation and PP1-dependent dephosphorylation.
磷脂酰肌醇4 - 磷酸5 - 激酶（PIPK）催化脂质信号分子磷脂酰肌醇4,5 - 二磷酸（PIP(2)）合成的最后一步。在完整细胞中，严格调控PIPK活性被认为至关重要。在此我们表明，PIPK的I型酶（PIPKI）被环磷酸腺苷依赖性蛋白激酶（PKA）磷酸化，且PIPKI的磷酸化会抑制其活性。丝氨酸214被发现是PKA催化的Iα型PIPK（PIPKIα）的主要磷酸化位点。相反，溶血磷脂酸诱导的蛋白激酶C激活会增加PIPKIα的活性。PIPKIα的激活是由去磷酸化诱导的，该去磷酸化由冈田酸敏感的磷酸酶——蛋白磷酸酶1（PP1）催化。用PP1对PIPKIα进行体外去磷酸化增加了PIPK活性，表明PP1在溶血磷脂酸诱导的PIPKIα去磷酸化过程中发挥作用。这些结果强烈表明，NIH 3T3细胞中PIPKIα的活性受PKA依赖性磷酸化和PP1依赖性去磷酸化之间的可逆平衡调控。
