Myotubularin, a phosphatase deficient in myotubular myopathy, acts on phosphatidylinositol 3-kinase and phosphatidylinositol 3-phosphate pathway
Myotubularin, a phosphatase deficient in myotubular myopathy, acts on phosphatidylinositol 3-kinase and phosphatidylinositol 3-phosphate pathway
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DOI：
10.1093/oxfordjournals.hmg.a018913
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发表时间：
2000-09-22
影响因子：
3.5
通讯作者：
Mandel, JL
中科院分区：
文献类型：
--
作者：
Blondeau, F;Laporte, J;Mandel, JL
肌管性肌病(MTM1)是一种X连锁疾病，以新生儿严重的低张力和全身性肌肉无力为特征，病理特征提示肌肉纤维成熟障碍，MTM1基因编码一种具有磷酸酪氨酸磷酸酶共识的蛋白质(肌管蛋白)。它定义了一个至少由九个基因组成的家族，其中包括最近发现突变为隐性Charcot-Marie-Tooth病的抗磷酸酶hMTMR5/Sbf1和hMTMR2。肌管蛋白在体外具有双重特异性的蛋白磷酸酶活性。我们在体内对裂殖酵母的酪氨酸磷酸酶活性进行了测试，表明肌管蛋白不具有广泛的特异性酪氨酸磷酸酶活性。活性人肌管蛋白的表达抑制了S.pombe的生长，并诱导了一种类似于空泡蛋白分类(VPS)途径突变体的空泡表型，尤其是磷脂酰肌醇3-激酶(PI3K)Vps34突变体。在缺失内源性MTM同源基因的S.pombe细胞中，人肌管蛋白的表达降低了磷脂酰肌醇3-磷酸(P13P)的水平。我们已经创造了一个底物陷阱突变体，它在HeLa细胞中显示出对质膜投射(棘突)的重新定位，并且在S.pombe试验中是不活跃的。这个突变体，而不是野生型或磷酸酶位点突变体，能够免疫沉淀Vps34激酶活性。野生型肌管蛋白在体外也能直接去磷酸化P13P和P14P。因此，肌管蛋白可能通过下调PI3K活性和直接降解P13P来降低P13P水平。
Myotubular myopathy (MTM1) is an X-linked disease, characterized by severe neonatal hypotonia and generalized muscle weakness, with pathological features suggesting an impairment in maturation of muscle fibres, The MTM1 gene encodes a protein (myotubularin) with a phosphotyrosine phosphatase consensus. It defines a family of at least nine genes in man, including the antiphosphatase hMTMR5/Sbf1 and hMTMR2, recently found mutated in a recessive form of Charcot-Marie-Tooth disease. Myotubularin shows a dual specificity protein phosphatase activity in vitro. We have performed an in vivo test of tyrosine phosphatase activity in Schizosaccharomyces pombe, indicating that myotubularin does not have a broad specificity tyrosine phosphatase activity. Expression of active human myotubularin inhibited growth of S.pombe and induced a vacuolar phenotype similar to that of mutants of the vacuolar protein sorting (VPS) pathway and notably of mutants of VPS34, a phosphatidylinositol 3-kinase (PI3K). In S.pombe cells deleted for the endogenous MTM homologous gene, expression of human myotubularin decreased the level of phosphatidylinositol 3-phosphate (P13P). We have created a substrate trap mutant which shows relocalization to plasma membrane projections (spikes) in HeLa cells and was inactive in the S.pombe assay. This mutant, but not the wild-type or a phosphatase site mutant, was able to immunoprecipitate a VPS34 kinase activity. Wild-type myotubularin was also able to directly dephosphorylate P13P and P14P in vitro. Myotubularin may thus decrease P13P levels by down-regulating PI3K activity and by directly degrading P13P.