A TRAIL receptor-dependent synthetic lethal relationship between MYC activation and GSK3beta/FBW7 loss of function.

The MYC protooncogene is frequently deregulated in human cancers. Here, by screening a kinase-directed library of small inhibitory RNAs, we identify glycogen synthase kinase 3beta (GSK3beta) as a gene whose inactivation potentiates TNF-related apoptosis-inducing ligand death receptor-mediated apoptosis specifically in MYC-overexpressing cells. Small inhibitory RNA-induced silencing of GSK3beta prevents phosphorylation of MYC on T58, thereby inhibiting recognition of MYC by the E3 ubiquitin ligase component FBW7. Attenuating the GSK3beta-FBW7 axis results in stabilization of MYC, up-regulation of surface levels of the TNF-related apoptosis-inducing ligand death receptor 5, and potentiation of death receptor 5-induced apoptosis in vitro and in vivo. These results identify GSK3beta and FBW7 as potential cancer therapeutic targets and MYC as a critical substrate in the GSK3beta survival-signaling pathway. The results also demonstrate paradoxically that MYC-expressing tumors might be treatable by drug combinations that increase rather than decrease MYC oncoprotein function.