Flevaris Panagiotis, Stojanovic Aleksandra, Gong Haixia, Chishti Athar, Welch Emily, Du Xiaoping
Department of Pharmacology, University of Illinois at Chicago, Chicago, IL 60612, USA.
J Cell Biol. 2007 Nov 5;179(3):553-65. doi: 10.1083/jcb.200703185. Epub 2007 Oct 29.
Integrin-dependent cell spreading and retraction are required for cell adhesion, migration, and proliferation, and thus are important in thrombosis, wound repair, immunity, and cancer development. It remains unknown how integrin outside-in signaling induces and controls these two opposite processes. This study reveals that calpain cleavage of integrin beta(3) at Tyr(759) switches the functional outcome of integrin signaling from cell spreading to retraction. Expression of a calpain cleavage-resistant beta(3) mutant in Chinese hamster ovary cells causes defective clot retraction and RhoA-mediated retraction signaling but enhances cell spreading. Conversely, a calpain-cleaved form of beta(3) fails to mediate cell spreading, but inhibition of the RhoA signaling pathway corrects this defect. Importantly, the calpain-cleaved beta(3) fails to bind c-Src, which is required for integrin-induced cell spreading, and this requirement of beta(3)-associated c-Src results from its inhibition of RhoA-dependent contractile signals. Thus, calpain cleavage of beta(3) at Tyr(759) relieves c-Src-mediated RhoA inhibition, activating the RhoA pathway that confines cell spreading and causes cell retraction.
整合素依赖性细胞铺展和收缩是细胞黏附、迁移和增殖所必需的，因此在血栓形成、伤口修复、免疫和癌症发展中很重要。整合素外向内信号如何诱导和控制这两个相反的过程仍然未知。本研究表明，钙蛋白酶在酪氨酸（Tyr）759处对整合素β3的切割将整合素信号的功能结果从细胞铺展转变为收缩。在中国仓鼠卵巢细胞中表达抗钙蛋白酶切割的β3突变体导致凝块收缩缺陷和RhoA介导的收缩信号，但增强细胞铺展。相反，钙蛋白酶切割形式的β3未能介导细胞铺展，但抑制RhoA信号通路可纠正这一缺陷。重要的是，钙蛋白酶切割的β3未能结合整合素诱导细胞铺展所需的c-Src，而β3相关c-Src的这一需求源于其对RhoA依赖性收缩信号的抑制。因此，钙蛋白酶在酪氨酸759处对β3的切割解除了c-Src介导的RhoA抑制，激活了限制细胞铺展并导致细胞收缩的RhoA途径。
