Cooray P, Yuan Y, Schoenwaelder S M, Mitchell C A, Salem H H, Jackson S P
Department of Medicine, Monash Medical School, Victoria, Australia.
Biochem J. 1996 Aug 15;318 ( Pt 1)(Pt 1):41-7. doi: 10.1042/bj3180041.
Focal adhesion kinase (125 kDa form; pp125FAK) is a widely expressed non-receptor tyrosine kinase that is implicated in integrin-mediated signal transduction. We have identified a novel means of pp 125FAK regulation in human platelets, in which this kinase undergoes sequential proteolytic modification from the native 125 kDa form to 90, 45 and 40 kDa fragments in thrombin-, collagen- and ionophore A23187-stimulated platelets. The proteolysis of pp125FAK was prevented by pretreating platelets with the calpain inhibitors calpeptin or calpain inhibitor-1, and was reproduced in vitro by incubating immunoprecipitated pp125FAK with purified calpain. Proteolysis of pp125FAK resulted in a dramatic reduction in its autokinase activity and led to its dissociation from the cytoskeletal fraction of platelets. These studies define a novel signal-terminating role for calpain, wherein proteolytic modification of pp125FAK attenuates its autokinase activity and induces its subcellular relocation within the cell.
粘着斑激酶（125 kDa形式；pp125FAK）是一种广泛表达的非受体酪氨酸激酶，参与整合素介导的信号转导。我们在人血小板中发现了一种新的pp125FAK调节方式，在凝血酶、胶原和离子载体A23187刺激的血小板中，这种激酶经历了从天然的125 kDa形式到90、45和40 kDa片段的顺序蛋白水解修饰。用钙蛋白酶抑制剂钙肽素或钙蛋白酶抑制剂-1预处理血小板可阻止pp125FAK的蛋白水解，并且通过将免疫沉淀的pp125FAK与纯化的钙蛋白酶一起孵育可在体外重现这种蛋白水解。pp125FAK的蛋白水解导致其自身激酶活性显著降低，并导致其从血小板的细胞骨架部分解离。这些研究确定了钙蛋白酶的一种新的信号终止作用，其中pp125FAK的蛋白水解修饰减弱其自身激酶活性并诱导其在细胞内的亚细胞重新定位。
