Abstract 1269: Molecular changes underlying bortezomib sensitization of cancer cells to TRAIL-mediated apoptosis

Abstract We have previously shown that the proteasome inhibitor bortezomib (Velcade/PS-341) specifically sensitized certain human renal carcinoma (RCC) lines to apoptosis induced by the TNF family-member TRAIL. A comparison of RCC sensitized by bortezomib with those that remained resistant revealed no major bortezomib-induced changes in the levels of many apoptosis proteins. Also, when bortezomib treatment induced specific changes in protein levels (mcl-1, Bik and survivin) these changes did not directly correlate with subsequent sensitization or resistance to TRAIL apoptosis. In addition changes in surface expression of TRAIL receptors (DR4, DR5, DcR1, DcR2) following bortezomib treatment also did not correlate well with sensitization or resistance. By contrast, enhanced procaspase 8 activation following bortezomib pretreatment and TRAIL exposure was only observed in the sensitized RCC. This increase in procaspase 8 activation in cell extracts of sensitized RCC was observed using both enzyme assays as well as western blotting for activated (cleaved) caspase 8. Use of the apoptosis-resistant MCF-7 cell line demonstrated that bortezomib pretreatment increased caspase-8 activation on exposure to TRAIL even in the absence of subsequent downstream caspase activation and apoptosis. This suggests that bortezomib increases caspase-8 activation upstream at the death-inducing signaling complex (DISC). Furthermore, immunoprecipitation of the DISC demonstrated higher levels of active caspase 8 in the DISC of sensitized but not resistant RCC. Interestingly ACHN (a bortezomib-sensitized RCC) was also sensitized to TRAIL apoptosis when adherence was prevented by coating cell culture dishes with poly-HEMA. In parallel this loss of adherence abolished the sensitizing effects of bortezomib treatment. Bortezomib and poly-HEMA treatment of RCC both result in reduced cellular proliferation, and may change cell adherence properties. Whether both of these treatments sensitize RCC to TRAIL using common or distinct molecular pathways is under further investigation. Funded in part by DHSS #NO1-CO-12400 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1269.