Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510, USA.
J Cell Biol. 2012 Dec 10;199(6):1003-16. doi: 10.1083/jcb.201206095.
Plasma membrane phosphatidylinositol (PI) 4-phosphate (PtdIns4P) has critical functions via both direct interactions and metabolic conversion to PI 4,5-bisphosphate (PtdIns(4,5)P₂) and other downstream metabolites. However, mechanisms that control this PtdIns4P pool in cells of higher eukaryotes remain elusive. PI4KIIIα, the enzyme thought to synthesize this PtdIns4P pool, is reported to localize in the ER, contrary to the plasma membrane localization of its yeast homologue, Stt4. In this paper, we show that PI4KIIIα was targeted to the plasma membrane as part of an evolutionarily conserved complex containing Efr3/rolling blackout, which we found was a palmitoylated peripheral membrane protein. PI4KIIIα knockout cells exhibited a profound reduction of plasma membrane PtdIns4P but surprisingly only a modest reduction of PtdIns(4,5)P₂ because of robust up-regulation of PtdIns4P 5-kinases. In these cells, however, much of the PtdIns(4,5)P₂ was localized intracellularly, rather than at the plasma membrane as in control cells, along with proteins typically restricted to this membrane, revealing a major contribution of PI4KIIIα to the definition of plasma membrane identity.
质膜磷脂酰肌醇 4-磷酸（PtdIns4P）通过直接相互作用和代谢转化为磷脂酰肌醇 4,5-二磷酸（PtdIns（4,5）P₂）和其他下游代谢物发挥关键功能。然而，高等真核细胞中控制这种 PtdIns4P 池的机制仍然难以捉摸。PI4KIIIα 是合成这种 PtdIns4P 池的酶，据报道它定位于内质网，与酵母同源物 Stt4 定位于质膜相反。在本文中，我们表明 PI4KIIIα 作为包含 Efr3/rolling blackout 的进化保守复合物的一部分被靶向到质膜，我们发现 Efr3/rolling blackout 是一种棕榈酰化的外周膜蛋白。PI4KIIIα 敲除细胞表现出质膜 PtdIns4P 的显著减少，但令人惊讶的是 PtdIns(4,5)P₂ 的减少幅度较小，因为 PtdIns4P 5-激酶的表达显著上调。然而，在这些细胞中，大部分 PtdIns(4,5)P₂ 被定位在细胞内，而不是像对照细胞那样位于质膜上，同时还有通常局限于该膜的蛋白质，这表明 PI4KIIIα 对质膜身份的定义有很大贡献。
