Bachelder R E, Wendt M A, Fujita N, Tsuruo T, Mercurio A M
Division of Cancer Biology and Angiogenesis, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
J Biol Chem. 2001 Sep 14;276(37):34702-7. doi: 10.1074/jbc.M102806200. Epub 2001 Jul 19.
Epithelial cells undergo death receptor-dependent apoptosis when detached from matrix, a process termed anoikis. Activation of Akt/protein kinase B (PKB) by matrix attachment protects cells from anoikis. In this study, we establish a link between anoikis and Akt/PKB-mediated survival by demonstrating that Akt/PKB is cleaved by caspases in matrix-detached epithelial cells by a mechanism that involves death receptors. Reduced levels of Akt/PKB protein were observed in detached Madin-Darby canine kidney cells relative to cells attached to collagen. Equivalent levels of Akt/PKB, however, were detected in matrix-adherent and detached cells after inhibition of caspase activity or expression of an Akt/PKB mutant (D108+119A) that is resistant to caspase cleavage. The contribution of death domain-containing proteins to Akt/PKB cleavage was evidenced by the ability of dominant negative Fas-associated death domain to restore normal levels of Akt/PKB in matrix-detached cells. Importantly, expression of a cleavage-resistant Akt/PKB mutant protected matrix-detached cells from apoptosis. These studies suggest that members of the death receptor family promote the caspase-mediated cleavage of Akt/PKB and that this event contributes to anoikis.
上皮细胞从基质脱离时会经历死亡受体依赖性凋亡，这一过程称为失巢凋亡。基质附着激活Akt/蛋白激酶B（PKB）可保护细胞免于失巢凋亡。在本研究中，我们通过证明Akt/PKB在基质脱离的上皮细胞中被半胱天冬酶切割，建立了失巢凋亡与Akt/PKB介导的细胞存活之间的联系，该机制涉及死亡受体。相对于附着于胶原蛋白的细胞，在脱离的Madin-Darby犬肾细胞中观察到Akt/PKB蛋白水平降低。然而，在抑制半胱天冬酶活性或表达对半胱天冬酶切割具有抗性的Akt/PKB突变体（D108+119A）后，在基质附着和脱离的细胞中检测到等量的Akt/PKB。显性负性Fas相关死亡结构域能够恢复基质脱离细胞中正常水平的Akt/PKB，这证明了含死亡结构域的蛋白对Akt/PKB切割的作用。重要的是，表达抗切割的Akt/PKB突变体可保护基质脱离的细胞免于凋亡。这些研究表明，死亡受体家族成员促进半胱天冬酶介导的Akt/PKB切割，并且这一事件促成了失巢凋亡。
