MP85-13 FNIP CO-CHAPERONES PROTECT THE TUMOR SUPPRESSOR FLCN FROM UBIQUITINATION AND DEGRADATION IN THE PROTEASOME

Abstract

INTRODUCTION AND OBJECTIVES: Currently one of the major goals of cancer therapy is selective killing of cancer cells. TRAIL has attracted considerable attention due to its ability to kill tumor cells while sparing the normal ones. When TRAIL induces apoptosis, it binds to death receptor 4 (DR4) and 5(DR5). After that, TRAIL induces trimerization of death receptors to form a complex named deathinducing signaling complex (DISC), which in turn activates caspase-8, leading to the further activation of caspase-3 and subsequent apoptosis. However, the development of resistance to TRAIL, which mechanism is still not fully understood, in many tumor types appears as a major roadblock for the application of TRAIL-based cancer therapy. In recent years, many studies indicated synergistic effect between TRAIL and numerous agents which can be applied to overcome resistance and therefore enhance the tumor-killing ability of TRAIL. Diosmetin is an O-methylated flavone, a compound which can be isolated in Caucasian vetch. In this study, we investigated whether diosmetin can increase the tumor-killing ability of TRAIL and looked into the mechanisms. METHODS: Anti-proliferative activity of diosmetin alone or in combination with TRAIL was investigated by cell viability assays. Cell death was evaluated using PI/Annexin V staining and flow cytometer. Furthermore, changes of protein were also investigated by Western Blot. RESULTS: We found that diosmetin was capable of promoting anti-tumor ability of TRAIL in renal carcinoma cells (Fig 1). Further investigation showed that diosmetin can up-regulate the expression of DR5 but not DR4 in Caki cells. Silencing of DR5 can abolish the synergistic effect between diosmetin and TRAIL. Mechanistically, induction of DR5 by diosmetin was found to be p53-independent but relied on the expression of CHOP. Knockdown of CHOP abrogated diosmetin-induced DR5 expression and the related enhancement of TRAIL-mediated cell death. In addition diosmetin could also down-regulate the expression of several cell survival proteins. CONCLUSIONS: Our results indicated that diosmetin potentiate TRAIL-induced apoptosis in renal carcinoma cells which relies on the CHOP-dependent up-regulation of DR5. Source of Funding: none