Protein phosphatase 1α activity prevents oncogenic transformation
Protein phosphatase 1α activity prevents oncogenic transformation
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DOI：
10.1002/mc.20191
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发表时间：
2006-09-01
影响因子：
4.6
通讯作者：
Berndt, Norbert
中科院分区：
文献类型：
--
作者：
Liu, Cathy W. Y.;Wang, Rui-Hong;Berndt, Norbert
细胞周期蛋白依赖性激酶2 （Cdk2）在G(1)晚期磷酸化蛋白磷酸酶1 α (PP1 α)的Thr320，从而抑制其活性。抗磷酸化PP1 α T320A作为一个组成型活性（CA）突变体，通过阻止视网膜母细胞瘤蛋白（pRb）的磷酸化和失活，导致G阻滞晚期。PP1 α介导的G、阻滞和PP1 α在G晚期的磷酸化都需要pRb的存在，这表明PP1a是pRb通路的关键调节因子，而pRb通路在人类癌症中几乎总是发生突变。这些发现促使我们研究PP1 α是否干扰致癌转化。与PP1 α T320A共转染后，ras/cyclin D1转染后的NIH 3T3细胞形成灶的能力明显受到抑制，但PP1 α不受抑制。同样，表达PP1 α T320A或PPlaT320A与绿色荧光蛋白（GFP）融合的细胞，无论PP1a构建体是否与ras/cyclin D1共转染或转染到稳定转化的细胞中，都不能在软琼脂中形成菌落。过表达的野生型（Wt） PP1 α和GFP-PP1 α在Thr320中被磷酸化，这很可能解释了其缺乏作用。在Western blots （WB）中，GFP-PP1 α - T320A的表达与caspase-cleaved pRb和细胞死亡的形态学迹象相关。这些发现表明PP1a活性可以通过引起细胞周期阻滞和/或凋亡而不是恢复接触抑制或锚定依赖来覆盖致癌信号。(c) 2006 Wiley-Liss, Inc。
Cyclin-dependent kinase 2 (Cdk2) phosphorylates Thr320 of protein phosphatase 1 alpha (PP1 alpha) in late G(1), thereby inhibiting its activity. Phosphorylation-resistant PP1 alpha T320A, acting as a constitutively active (CA) mutant, causes a late G, arrest by preventing the phosphorylation and inactivation of the retinoblastoma protein (pRb). Both PP1 alpha-mediated G, arrest and PP1 alpha phosphorylation in late G, require the presence of pRb, indicating that PP1a is a crucial regulator of the pRb pathway, which is almost invariably mutated in human cancer. These findings prompted us to investigate whether PP1 alpha interferes with oncogenic transformation. The ability of NIH 3T3 cells to form foci after transformation with ras/cyclin D1 was significantly inhibited by co-transfection with PP1 alpha T320A, but not PP1 alpha. Likewise, cells expressing PP1 alpha T320A or PPlaT320A fused to green fluorescent protein (GFP) were unable to form colonies in soft agar, regardless of whether PP1a constructs were co-transfected with ras/cyclin D1 or transfected into stably transformed cells. Overexpressed wild-type (Wt) PP1 alpha and GFP-PP1 alpha were phosphorylated in Thr320, most likely explaining its lack of effect. Expression of GFP-PP1 alpha T320A was associated with caspase-cleaved pRb in Western blots (WB) and morphological signs of cell death. These findings demonstrate that PP1a activity can override oncogenic signaling by causing cell-cycle arrest and/or apoptosis rather than restoring contact inhibition or anchorage dependence. (c) 2006 Wiley-Liss, Inc.