The role of intracellular phospholipase Al family in the maintenance of cellular compartments and membrane traffic

哺乳动物细胞内磷脂酶A1家族由三个成员组成，即偏爱磷脂酸的磷脂酶A1(PA-PLA1)、p125和KIAA0725p。在之前的研究中，我们证明了p125是内质网出口部位的哺乳动物特有的成分，并参与了这个间隔的组织。在本研究中，我们研究了KIAA0725p的功能。1)为了解KIAA0725p的功能，RNAi以KIAA0725p为靶点进行降解。在KIAA0725P耗竭的细胞中，高尔基体的组织受到微妙的影响。VSV-G蛋白从高尔基体到质膜的转运以及志贺毒素从质膜到高尔基体的转运都受到了影响。这些结果表明KIAA0725p参与了高尔基体和质膜之间的蛋白质转运。2)从Sf9细胞中纯化重组蛋白，并分析其与各种磷脂的结合。我们发现p125和KIAA0725P与磷脂酰肌醇3-磷酸(PI3P)、PI4P和PI5P结合。另一方面，在相同的条件下，PA-PLA1不与任何脂质结合。KIAA0725P和PA-PLA1分别定位于高尔基体和胞浆。这些结果提示PIP可能是p125和KIAA0725p的膜受体。

The mammalian intracellular phospholipase A1 family consists of three members, phosphatidic acid-preferring phospholipase A1 (PA-PLA1), p125, and KIAA0725p. In a previous study, we showed that p125 is a mammalian-specific component of ER exit sites and participates in the organization of this compartment. In this study, we examined the function of KIAA0725p. In addition, the binding affinity of three proteins to various phospholipids was analyzed.1) To gain insight into the function of KIAA0725p, KIAA0725p mRNA was targeted for degradation by RNAi. In KIAA0725p-depleted cells, the organization of the Golgi apparatus was subtly affected. VSV-G Protein transport from the Golgi to plasma membrane and Shiga-toxin transport from the plasma membrane to the Golgi were affected in these cells. These results suggest that KIAA0725p participates in protein transport between the Golgi and the plasma membrane.2) Recombinant proteins were purified from Sf9 cells and used to analyze their binding to various phoispholipids. We found that p125 and KIAA0725p bind to phosphatidylinositol 3-phosphate (PI3P), PI4P, and PI5P. On the other hand, PA-PLA1 did not bind to any lipids under the same condition. KIAA0725p and PA-PLA1localize to the Golgi apparatus and the cytosol, respectively. These results rise the possibility that PIP is a membrane receptor for p125 and KIAA0725p.