Abstract 1978: The poly-SUMO protein specific E3 ubiquitin ligase RNF4 is induced in multiple myeloma and reduces bortezomib-induced cell killing

Abstract

Abstract Multiple Myeloma (MM) is a fatal neoplasm of B-cell origin characterized by the clonal proliferation and accumulation of malignant plasma cells in the bone marrow. While recent advances in mechanistic understanding and treatment modalities have extended median survival to >6 years and 10% of patients survive >10 years, the vast majority of MM remains incurable with conventional, high dose therapy or stem cell transplantation. Bortezomib is a selective, reversible inhibitor of the 26S proteasome that inhibits protein degradation and is now FDA-approved for the treatment of newly diagnosed, relapsed and refractory MM. Though the catabolism of ubiquitinated substrates has been targeted therapeutically with significantly improved prognosis, patient response to bortezomib remains highly variable and cannot be predicted accurately. E3 ligases confer specificity on target selection for Ub+proteasome degradation. We therefore analyzed the expression of individual E3's using a microarray dataset obtained from MM patient tumor samples and found a striking variability in the expression level of individual E3 ligases between normal plasma cells and patients MM cells. RNF4, an E3 specific for poly-sumoylated proteins, was induced in MM patients and correlated with decreased patient response to the proteasome inhibitor bortezomib. Expression profiling of pretreatment tumor samples obtained from MM patients in independent clinical trials were used to generate a signature that correlated expression of SUMO+Ub+Proteasome pathway components with clinical outcome to predict patient response to bortezomib. Experimental validation by overexpression of RNF4-wt rendered myeloma cell lines relatively resistant to bortezomib while RNF4 depletion by shRNA enhanced sensitivity to bortezomib. Transfection of HA-tagged SUMO followed by bortezomib exposure led to the accumulation of HA-SUMO∼conjugates that were immunoreactive with Ub and proteasome components to further link the pathways. In summary, RNF4 an E3 ligase specific for SUMO-conjugates and induced in myeloma, modulates the cellular response to proteasome-based therapy and promotes bortezomib resistance. Our results support regulators of the sumoylation pathway as biomarkers to predict clinical response to bortezomib and provide evidence for targeting SUMO pathway to improve therapeutic outcome in myeloma in general and bortezomib specifically. 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 1978.