Inhibition of proteasome activity sensitizes human granulosa tumor cells to TRAIL-induced cell death

Human granulosa tumor cell (GCT) lines (KGN and COV434) were utilized to establish the combinatorial effects of TRAIL treatment and a proteasome inhibitor on cell viability, in vitro. TRAIL induced a slight, but consistent, decrease in viability for both cell lines, and pharmacologic inhibition of proteasome activity, using Z-LLF-CHO (Z-LLF), synergistically enhanced TRAIL-induced loss of viability. This enhanced sensitization was associated with the up-regulation of a TRAIL receptor, DR5, and pro-apoptotic Bax. Targeted reduction of p53 expression revealed that the ability of Z-LLF to enhance DR5 and Bax expression occurs independent of p53 activity. These studies underscore the potential to develop targeted treatments for GCTs using established cell lines.