Role of PIP2 and PIP3 binding proteins on cell growth signals

1.组蛋白作为新的PIP_2结合蛋白我们发现PIP_2与组蛋白H_1和H_3结合，并确定了结合部位。PIP_2与C-端103个氨基酸结合。当组蛋白H_1被PKC磷酸化时，与组蛋白H_1结合的PIP_2的量减少。在组蛋白H_1中加入PIP_2可抑制组蛋白H_1对RNA聚合酶碱性转录活性的抑制作用。酪氨酸激酶下游的PIP_2磷酸酶我们从牛脑中纯化了与Ash/Grb2结合的150 kDa蛋白，并分离出其cDNA。P150与突触素具有同源性。当P150在Cos细胞中表达时，肌动蛋白应激纤维断裂，细胞呈多核形态。我们从牛脑中提纯了P150，并对其进行了鉴定。肌动蛋白调节蛋白Cofilin、Profilin和α-Actinin对PIP2磷酸酶活性无抑制作用，而对PLCdelta1有抑制作用。这些结果表明，P150能使PIP_2与肌动蛋白调节蛋白结合，导致肌动蛋白纤维的重组。

1. Histons as novel PIP_2 binding proteinsWe found that PIP_2 bound to histon H_1 and H_3 and determined the binding sites. PIP_2 bound to the C-terminal 103 aminoacids. The amounts of PIP_2 bound to histon H_1 decreased when histon H_1 was phosphorylated by PKC.The addition of PIP_2 to histon H_1 suppressed the inhibitory effect of histon H_1 on basic transcriptional activity by RNA polymerase.2. PIP_2 phosphatase downstream of tyrosine kinaseWe purified 150kDa protein bound to Ash/Grb2 from bovine brain, and isolated its cDNA.P150 was found to have homology with synaptojanin. When P150 was expressed in Cos cells, actin stress fibers was disrupted and the cells showed multi-nuclear in shape. We purified P150 from bovine brain and characterized it. PIP_2 phosphatase activity was not inhibited by actin regulatory proteins such as cofilin, profilin and alpha-actinin, While PLCdelta_1 was inhibited. These results suggest that P150 hydrolyzes PIP_2 bound to actin regulatory proteins, resulting in reorganization of actin fibers.