The phosphatase PHLPP controls the cellular levels of protein kinase C
The phosphatase PHLPP controls the cellular levels of protein kinase C
复制标题
DOI：
10.1074/jbc.m707319200
复制
发表时间：
2008-03-07
影响因子：
4.8
通讯作者：
Newton, Alexandra C.
中科院分区：
文献类型：
--
作者：
Gao, Tianyan;Brognard, John;Newton, Alexandra C.
蛋白激酶C （PKC）的生命周期由多个磷酸化和去磷酸化步骤控制。PKC的成熟需要三个有序的磷酸化，一个在激活环上，两个在cooh末端，转动基序和疏水基序上，以产生稳定的和具有信号能力的酶。这种酶的去磷酸化导致蛋白质降解。我们最近发现了一个新的蛋白磷酸酶家族，称为PH结构域富亮氨酸重复蛋白磷酸酶（PHLPP），其成员通过去磷酸化Akt上的疏水基序来终止Akt信号传导。在这里，我们发现两个PHLPP亚型，PHLPP1和PHLPP2，也会使PKC β II上的疏水基序去磷酸化，这一事件将PKC转移到洗涤剂不溶部分，有效地终止其生命周期。缺失突变表明PH结构域对于PHLPP在细胞中有效地去磷酸化PKC β II是必需的，而Akt调控所需的pdz结合基序则是可缺性的。phobol酯介导的疏水位点的去磷酸化，而不是旋转基序或激活环，对冈田酸不敏感，这与PP2C家族成员PHLPP控制疏水位点一致。此外，敲低PHLPP的表达降低了phobol酯引发的PKC α疏水基序的去磷酸化速率，但不影响转过基序的去磷酸化速率。最后，我们发现结肠癌和正常乳腺上皮细胞中PHLPP的消耗导致传统和新型PKC水平的增加。这些数据表明，PHLPP通过特异性地去磷酸化疏水基序来控制PKC的细胞水平，从而使酶不稳定并促进其降解。
The life cycle of protein kinase C (PKC) is controlled by multiple phosphorylation and dephosphorylation steps. The maturation of PKC requires three ordered phosphorylations, one at the activation loop and two at COOH-terminal sites, the turn motif and the hydrophobic motif, to yield a stable and signaling-competent enzyme. Dephosphorylation of the enzyme leads to protein degradation. We have recently discovered a novel family of protein phosphatases named PH domain leucine-rich repeat protein phosphatase (PHLPP) whose members terminate Akt signaling by dephosphorylating the hydrophobic motif on Akt. Here we show that the two PHLPP isoforms, PHLPP1 and PHLPP2, also dephosphorylate the hydrophobic motif on PKC beta II, an event that shunts PKC to the detergent-insoluble fraction, effectively terminating its life cycle. Deletion mutagenesis reveals that the PH domain is necessary for the effective dephosphorylation of PKC beta II by PHLPP in cells, whereas the PDZ-binding motif, required for Akt regulation, is dispensable. The phorbol ester-mediated dephosphorylation of the hydrophobic site, but not the turn motif or activation loop, is insensitive to okadaic acid, consistent with PHLPP, a PP2C family member, controlling the hydrophobic site. In addition, knockdown of PHLPP expression reduces the rate of phorbol ester-triggered dephosphorylation of the hydrophobic motif, but not turn motif, of PKC alpha. Last, we show that depletion of PHLPP in colon cancer and normal breast epithelial cells results in an increase in conventional and novel PKC levels. These data reveal that PHLPP controls the cellular levels of PKC by specifically dephosphorylating the hydrophobic motif, thus destabilizing the enzyme and promoting its degradation.