Phosphorylation of murine caspase-9 by the protein kinase casein kinase 2 regulates its cleavage by caspase-8
Phosphorylation of murine caspase-9 by the protein kinase casein kinase 2 regulates its cleavage by caspase-8
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DOI：
10.1074/jbc.m802846200
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发表时间：
2008-07-18
影响因子：
4.8
通讯作者：
Kelekar, Ameeta
中科院分区：
文献类型：
--
作者：
McDonnell, Maureen A.;Abedin, Md. Joynal;Kelekar, Ameeta
我们实验室之前的研究表明，细胞色素c非依赖性加工和caspase-8对caspase-9的激活有助于肿瘤坏死因子(TNF) α处理的小鼠细胞中caspase级联的早期扩增。在这里，我们发现小鼠caspase-9在caspase-8切割位点附近的丝氨酸上被酪蛋白激酶2 （CK2）磷酸化。CK2已被证明通过磷酸化caspase-8切割位点附近的丝氨酸残基来调节促凋亡Bid蛋白的切割。同样，CK2修饰caspase-9上的Ser（348）似乎使该蛋白酶不易被活性caspase-8切割。这种磷酸化不影响caspase-9的自动加工能力。替换Ser（348）可消除磷酸化，但不能消除切割，在tnf α处理的caspase-9敲除小鼠胚胎成纤维细胞中，磷酸化位点突变可促进细胞凋亡。此外，CK2活性的抑制和RNA干扰介导的激酶的敲低加速了caspase-9的激活，而磷酸酶的抑制延迟了caspase-9的激活和死亡，以响应TNF受体的占领。综上所述，这些研究表明TNF受体交联促进caspase-9的去磷酸化，使其易于被活化的caspase-8蛋白加工。因此，我们的数据表明，对procaspase-9进行修饰以保护其免受不适当的切割和激活是致癌激酶CK2促进生存的另一种机制。
Previous studies from our laboratory had indicated that cytochrome c-independent processing and activation of caspase-9 by caspase-8 contributed to early amplification of the caspase cascade in tumor necrosis factor (TNF)-alpha-treated murine cells. Here we show that murine caspase-9 is phosphorylated by casein kinase 2 (CK2) on a serine near the site of caspase-8 cleavage. CK2 has been shown to regulate cleavage of the pro-apoptotic Bid protein by phosphorylating serine residues near its caspase-8 cleavage site. Similarly, CK2 modification of Ser(348) on caspase-9 appears to render the protease refractory to cleavage by active caspase-8. This phosphorylation did not affect the ability of caspase-9 to autoprocess. Substitution of Ser(348) abolished phosphorylation but not cleavage, and a phospho-site mutant promoted apoptosis in TNF-alpha-treated caspase-9 knock-out mouse embryo fibroblasts. Furthermore, inhibition of CK2 activity and RNA interference-mediated knockdown of the kinase accelerated caspase-9 activation, whereas phosphatase inhibition delayed both caspase-9 activation and death in response to TNF receptor occupation. Taken together, these studies show that TNF receptor cross-linking promotes dephosphorylation of caspase-9, rendering it susceptible to processing by activated caspase-8 protein. Thus, our data suggest that modification of procaspase-9 to protect it from inappropriate cleavage and activation is yet another mechanism by which the oncogenic kinase CK2 promotes survival.