PDF(Pubmed)
Abstract：
KRAS is a small GTPase, ubiquitously expressed in mammalian cells, that functions as a molecular switch to regulate cell proliferation and differentiation. Oncogenic mutations that render KRAS constitutively active occur frequently in human cancers. KRAS must localize to the plasma membrane (PM) for biological activity. KRAS PM binding is mediated by interactions of the KRAS membrane anchor with phosphatidylserine (PtdSer), therefore, depleting PM PtdSer content abrogates KRAS PM binding and oncogenic function. From a genome-wide siRNA screen to search for genes that regulate KRAS PM localization, we identified a set of phosphatidylinositol (PI) 3-phosphatase family members: myotubularin-related (MTMR) proteins 2, 3, 4 and 7. Here we show that knockdown of MTMR 2/3/4/7 expression disrupts KRAS PM interactions. The molecular mechanism involves depletion of PM PI 4-phosphate (PI4P) levels, which in turn disrupts the subcellular localization and operation of oxysterol-binding protein related protein (ORP) 5, a PtdSer lipid transfer protein that maintains PM PtdSer content. Concomitantly, silencing MTMR 2/3/4/7 expression elevates PM levels of PI3P and reduces PM and total cellular levels of PtdSer. In summary we propose that the PI 3-phosphatase activity provided by MTMR proteins is required to generate PM PI for the synthesis of PM PI4P, which in turn, promotes the PM localization of PtdSer and KRAS.
摘要：
KRAS是一种小的GTPase,在哺乳动物细胞中普遍表达，作为调节细胞增殖和分化的分子开关。使KRAS具有组成活性的致癌突变在人类癌症中频繁发生。KRAS必须定位于质膜(PM)以获得生物活性。KRASPM结合由KRAS膜锚与磷脂酰丝氨酸（PtdSer）的相互作用介导，因此,消耗PMPtdSer含量消除了KRASPM结合和致癌功能。从全基因组siRNA筛选中寻找调节KRASPM定位的基因，我们确定了一组磷脂酰肌醇（PI）3-磷酸酶家族成员：肌管蛋白相关（MTMR）蛋白2，3，4和7。在这里，我们显示了MTMR2/3/4/7表达的敲低会破坏KRASPM相互作用。分子机制涉及PMPI4-磷酸（PI4P）水平的消耗，反过来又破坏了氧固醇结合蛋白相关蛋白（ORP）5的亚细胞定位和操作，该蛋白是PtdSer脂质转移蛋白，可维持PMPtdSer含量。同时，沉默MTMR2/3/4/7表达会提高PI3P的PM水平，并降低PM和PtdSer的总细胞水平。总之，我们建议MTMR蛋白提供的PI3-磷酸酶活性是产生PMPI合成PMPI4P所必需的，反过来，促进PtdSer和KRAS的PM本地化。
