Mecanismes de la resistance intrinseque a l'apoptose induite par TRAIL chez les cellules de cancer ovarien par

Epithelial ovarian cancer (EOC) cells often show increased activity of the PI3K/Akt pathway. In addition, we have previously shown that EOC ascites induce Akt activation in the tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-sensitive EOC cell line, CaOV3, leading to TRAIL-mediated apoptosis inhibition. In this study, we investigated the role of Akt in intrinsic resistance to TRAIL, which is common in EOC cells. We report that Akt activation reduces the sensitivity of EOC cells to TRAIL. TRAILresistant SKOV3ipl and COV2 cells were sensitized to TRAIL-induced apoptosis by PI3K or Akt inhibitors although inhibition of PI3K/Akt signaling pathway did not interfere with the recruitment and processing of caspase-8 to the death-inducing signaling complex. Conversely, overexpression of Aktl in TRAIL-sensitive cells promoted resistance to TRAIL. Although the fact that TRAIL-induced caspase-8 activation was observed in both sensitive and resistant cell lines, Bid cleavage occurred only in sensitive cells or in SKOV3ipl cells treated with LY294002. Bid expression was low in resistant cells and Akt activation downregulated its expression. Depletion of Bid by siRNA in OVCAR3 cells was associated with a decrease in TRAIL-mediated apoptosis. Overexpression of Bid only in SKOV3ipl cells enhanced TRAIL-induced apoptosis. Simultaneous blockade of Akt pathway further increased TRAIL-induced apoptosis. Thus, Akt acts upstream of mitochondria and inhibits TRAIL-induced apoptosis by decreasing Bid protein levels and possibly inhibiting its cleavage. Oncogene (2010) 29, 5523-5536; doi:10.1038/onc.2010.288; published online 26 July 2010.