LaLonde David P, Brown Michael C, Bouverat Brian P, Turner Christopher E
Department of Cell and Developmental Biology, State University of New York Upstate Medical University, Syracuse, New York 13210, USA.
J Biol Chem. 2005 Jun 3;280(22):21680-8. doi: 10.1074/jbc.M500752200. Epub 2005 Apr 6.
The focal adhesion protein actopaxin contributes to integrin-actin associations and is involved in cell adhesion, spreading, and motility. Herein, we identify and characterize an association between actopaxin and the serine/threonine kinase testicular protein kinase 1 (TESK1), a ubiquitously expressed protein previously reported to regulate cellular spreading and focal adhesion formation via phosphorylation of cofilin. The interaction between actopaxin and TESK1 is direct and the binding sites were mapped to the carboxyl terminus of both proteins. The association between actopaxin and TESK1 is negatively regulated by adhesion to fibronectin, and a phosphomimetic actopaxin mutant that promotes cell spreading also exhibits impaired binding to TESK1. Binding of actopaxin to TESK1 inhibits TESK1 kinase activity in vitro. Expression of the carboxyl terminus of actopaxin has previously been reported to retard cell spreading. This effect was reversed following overexpression of TESK1 and was found to be dependent on an inability of actopaxin carboxyl terminus expressing cells to promote cofilin phosphorylation upon matrix adhesion and caused by retention of TESK1 by this actopaxin mutant. Thus, the association between actopaxin and TESK1, which is likely regulated by phosphorylation of actopaxin, regulates TESK1 activity and subsequent cellular spreading on fibronectin.
粘着斑蛋白桩蛋白有助于整合素与肌动蛋白的结合，并参与细胞粘附、铺展和迁移。在此，我们鉴定并表征了桩蛋白与丝氨酸/苏氨酸激酶睾丸蛋白激酶1（TESK1）之间的关联，TESK1是一种普遍表达的蛋白，此前报道其通过对丝切蛋白的磷酸化来调节细胞铺展和粘着斑形成。桩蛋白与TESK1之间的相互作用是直接的，结合位点定位于两种蛋白的羧基末端。桩蛋白与TESK1之间的关联受到与纤连蛋白粘附的负调控，促进细胞铺展的模拟磷酸化桩蛋白突变体也表现出与TESK1的结合受损。桩蛋白与TESK1的结合在体外抑制TESK1激酶活性。此前报道桩蛋白羧基末端的表达会阻碍细胞铺展。在过表达TESK1后这种效应被逆转，并且发现这取决于表达桩蛋白羧基末端的细胞在基质粘附时无法促进丝切蛋白磷酸化，以及该桩蛋白突变体对TESK1的保留。因此，桩蛋白与TESK1之间的关联可能受桩蛋白磷酸化调控，它调节TESK1活性以及随后细胞在纤连蛋白上的铺展。
