Duex Jason E, Tang Fusheng, Weisman Lois S
Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.
J Cell Biol. 2006 Feb 27;172(5):693-704. doi: 10.1083/jcb.200512105. Epub 2006 Feb 21.
Phosphoinositide-signaling lipids function in diverse cellular pathways. Dynamic changes in the levels of these signaling lipids regulate multiple processes. In particular, when Saccharomyces cerevisiae cells are exposed to hyperosmotic shock, PI3,5P2 (phosphatidylinositol [PI] 3,5-bisphosphate) levels transiently increase 20-fold. This causes the vacuole to undergo multiple acute changes. Control of PI3,5P2 levels occurs through regulation of both its synthesis and turnover. Synthesis is catalyzed by the PI3P 5-kinase Fab1p, and turnover is catalyzed by the PI3,5P2 5-phosphatase Fig4p. In this study, we show that two putative Fab1p activators, Vac7p and Vac14p, independently regulate Fab1p activity. Although Vac7p only regulates Fab1p, surprisingly, we find that Vac14 regulates both Fab1p and Fig4p. Moreover, Fig4p itself functions in both PI3,5P2 synthesis and turnover. In both the absence and presence of Vac7p, the Vac14p-Fig4p complex controls the hyperosmotic shock-induced increase in PI3,5P2 levels. These findings suggest that the dynamic changes in PI3,5P2 are controlled through a tight coupling of synthesis and turnover.
磷酸肌醇信号脂在多种细胞途径中发挥作用。这些信号脂水平的动态变化调节着多个过程。特别是，当酿酒酵母细胞受到高渗冲击时，PI3,5P2（磷脂酰肌醇[PI]3,5-二磷酸）水平会瞬时增加20倍。这会导致液泡发生多种急性变化。PI3,5P2水平的控制通过其合成和周转的调节来实现。合成由PI3P 5-激酶Fab1p催化，周转由PI3,5P2 5-磷酸酶Fig4p催化。在本研究中，我们表明两个假定的Fab1p激活剂Vac7p和Vac14p独立调节Fab1p活性。虽然Vac7p只调节Fab1p，但令人惊讶的是，我们发现Vac14既调节Fab1p又调节Fig4p。此外，Fig4p自身在PI3,5P2的合成和周转中都发挥作用。无论有无Vac7p，Vac14p-Fig4p复合物都控制着高渗冲击诱导的PI3,5P2水平的增加。这些发现表明，PI3,5P2的动态变化是通过合成和周转的紧密耦合来控制的。
