Tang D, Gururajan R, Kidd V J
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101, USA.
J Biol Chem. 1998 Jun 26;273(26):16601-7. doi: 10.1074/jbc.273.26.16601.
A number of cellular proteins have been identified as caspase targets during cell death, including the PITSLRE protein kinases. These targets generally fall into one of three possible categories: 1) other caspases, 2) proteins that are inactivated during apoptosis, and 3) proteins that are required for execution of the cell death program. However, not all proteins are cleaved by caspases during apoptosis. Why only specific proteins are destined to be processed by caspases during cell death is currently not clear. Here we show that multiple caspase-like activities are involved in the processing of the PITSLRE p110 isoforms during Fas-induced apoptosis in Jurkat T-cells. Three p110 caspase cleavage sites have been mapped to the amino-terminal domain of p110 and verified by site-directed mutagenesis. Curiously, the mutagenesis studies revealed that cleavage of two juxtaposed caspase sites is necessary for the complete processing of this protein during cell death in vivo. Finally, we demonstrate that the PITSLRE p110 protein is rapidly phosphorylated during Fas-induced apoptosis in Jurkat cells and that phosphorylation of an amino-terminal portion of the protein may enhance caspase cleavage in this region.
在细胞死亡过程中，许多细胞蛋白已被确定为半胱天冬酶的作用靶点，包括PITSLRE蛋白激酶。这些靶点通常可分为以下三种可能的类别之一：1）其他半胱天冬酶，2）在细胞凋亡过程中失活的蛋白，3）执行细胞死亡程序所需的蛋白。然而，并非所有蛋白在细胞凋亡过程中都会被半胱天冬酶切割。目前尚不清楚为什么在细胞死亡过程中只有特定的蛋白会被半胱天冬酶加工处理。在此我们表明，在Jurkat T细胞中，Fas诱导的细胞凋亡过程中，多种类半胱天冬酶活性参与了PITSLRE p110亚型的加工处理。已将三个p110半胱天冬酶切割位点定位到p110的氨基末端结构域，并通过定点诱变进行了验证。奇怪的是，诱变研究表明，在体内细胞死亡过程中，两个相邻的半胱天冬酶位点的切割对于该蛋白的完全加工处理是必要的。最后，我们证明在Jurkat细胞中，Fas诱导的细胞凋亡过程中，PITSLRE p110蛋白会迅速磷酸化，并且该蛋白氨基末端部分的磷酸化可能会增强该区域的半胱天冬酶切割。
