The cleavage of Akt/protein kinase B by death receptor signaling is an important event in detachment-induced apoptosis.
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.
Bachelder
R E
RE
Division of Cancer Biology and Angiogenesis, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA. rbacheld@caregroup.harvard.edu
Wendt
M A
MA
Fujita
N
N
Tsuruo
T
T
Mercurio
A M
AM
D000818:Animals; D023102:Anoikis; D017209:Apoptosis; D020169:Caspases / Q000502:physiology; D002460:Cell Line; D004285:Dogs; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D053219:Receptors, Tumor Necrosis Factor, Member 25
D011518:Proto-Oncogene Proteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053219:Receptors, Tumor Necrosis Factor, Member 25; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; C506033:TNFRSF25 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020169:Caspases