The Neurosecretory Vesicle Protein Phogrin Functions as a Phosphatidylinositol Phosphatase to Regulate Insulin Secretion
The Neurosecretory Vesicle Protein Phogrin Functions as a Phosphatidylinositol Phosphatase to Regulate Insulin Secretion
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DOI：
10.1074/jbc.m109.066563
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发表时间：
2010-04-02
影响因子：
4.8
通讯作者：
Bowen-Pope, Daniel F.
中科院分区：
文献类型：
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作者：
Caromile, Leslie A.;Oganesian, Anush;Bowen-Pope, Daniel F.
寡聚蛋白是在具有刺激偶联肽激素分泌的细胞（包括胰腺β细胞）中表达的跨膜蛋白，其中其定位于含胰岛素的致密核心囊泡的膜。根据序列，phogrin是受体样蛋白酪氨酸磷酸酶家族的成员，但它在保守的催化序列中含有取代，并且从未报道过phogrin的显著酶活性。我们在这里报告，phogrin能够去磷酸化特定的肌醇磷脂，包括磷脂酰肌醇（PI）3-磷酸和PI 4，5-二磷酸，但不是PI 3，4，5-三磷酸。磷脂酰肌醇磷酸酶（PIPase）活性的phogrin是可测量的，但低的催化结构域融合蛋白水解可溶性短链磷脂酰肌醇磷脂的能力进行评估时。与大多数PIP酶（其是与膜缔合的细胞质蛋白）不同，成熟的磷酸蛋白是跨膜蛋白。当跨膜形式的磷酸蛋白在哺乳动物细胞中过表达时，它以剂量依赖性方式降低质膜磷脂酰肌醇4，5-二磷酸水平。当纯化和体外测定时，跨膜形式具有142 mol/min/mol的比活性，比催化结构域融合蛋白活性高75倍，并且与其他PIP酶的比活性相当。磷酸根蛋白的PIPase活性依赖于催化位点半胱氨酸，并与葡萄糖刺激的胰岛素分泌的影响。我们建议，phogrin功能作为一个磷脂酰肌醇磷酸酶，有助于维持PIP水平的亚细胞差异，这是重要的调节刺激耦合的胰岛素胞吐作用。
Phogrin is a transmembrane protein expressed in cells with stimulus-coupled peptide hormone secretion, including pancreatic beta cells, in which it is localized to the membrane of insulin-containing dense-core vesicles. By sequence, phogrin is a member of the family of receptor-like protein-tyrosine phosphatases, but it contains substitutions in conserved catalytic sequences, and no significant enzymatic activity for phogrin has ever been reported. We report here that phogrin is able to dephosphorylate specific inositol phospholipids, including phosphatidylinositol (PI) 3-phosphate and PI 4,5-diphosphate but not PI 3,4,5-trisphosphate. The phosphatidylinositol phosphatase (PIPase) activity of phogrin was measurable but low when evaluated by the ability of a catalytic domain fusion protein to hydrolyze soluble short-chain phosphatidylinositol phospholipids. Unlike most PIPases, which are cytoplasmic proteins that associate with membranes, mature phogrin is a transmembrane protein. When the transmembrane form of phogrin was overexpressed in mammalian cells, it reduced plasma membrane phosphatidylinositol 4,5-disphosphate levels in a dose-dependent manner. When purified and assayed in vitro, the transmembrane form had a specific activity of 142 mol/min/mol, 75-fold more active than the catalytic domain fusion protein and comparable with the specific activities of the other PIPases. The PIPase activity of phogrin depended on the catalytic site cysteine and correlated with effects on glucose-stimulated insulin secretion. We propose that phogrin functions as a phosphatidylinositol phosphatase that contributes to maintaining subcellular differences in levels of PIP that are important for regulating stimulus-coupled exocytosis of insulin.