Chemotherapeutic drugs sensitize cancer cells to TRAIL-mediated apoptosis: up-regulation of DR5 and inhibition of Yin Yang 1

Several chemotherapeutic drugs in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) result in reversal of resistance to TRAIL-mediated apoptosis through up-regulation of DR5 expression. The promoter of DR5 has one putative binding site for the transcription repressor in Yang 1 (YY1), and thus, we hypothesized that the sensitizing drugs may inhibit YY1. We have found that treatment of tumor cells with various chemotherapeutic drugs inhibited nuclear factor-kappa B. We examined whether drugs also inhibit YY1 activity and whether YY1 inhibition correlates with up-regulation of DR5 expression and sensitization of cells to TRAIL-induced apoptosis. The TRAIL- and drug-resistant prostate carcinoma PC-3 cell line was treated with CDDP, VP-16, ADR, and vincristine. DR5 luciferase reporter constructs and small interfering RNA against YY1 were used to determine the role of YY1 in DR5 transcription. Pretreatment of PC-3 cells and other tumor cell lines with various chemotherapeutic drugs sensitized the cells to TRAIL-induced apoptosis concurrently with up-regulation of DR5 expression and inhibition of YY1 expression and its DNA-binding activity. The baseline luciferase activity in PC-3 cells transfected with the wildtype DR5 reporter was significantly augmented in cells transfected with DR5 constructs carrying deletions or mutation in the YY1-binding site. Treatment with drug enhanced DR5 wild-type luciferase activity, with no increase in cells transfected with the YY1-deleted or YY1-mutated constructs. Cells transfected with YY1 small interfering RNA showed up-regulation of DR5 expression and sensitization to TRAIL-mediated apoptosis. The findings provide evidence that drug-induced sensitization of tumor cells to TRAIL is mediated, in part, by inhibition of the transcription repressor YY1 and up-regulation of DR5 expression. Hence, YY1 may be a potential therapeutic target to reverse resistance to TRAIL-induced apoptosis.