E3 Ligase c-CBL Mediates Ubiquitination-Proteasomal Degradation of BCR-ABL and Therapeutic Effects against BCR-ABL Leukemia.

Abstract

Abstract 3257Poster Board III-1We previously demonstrated that the cellular level of the fusion oncoprotein BCR-ABL in chronic myelogenous leukemia (CML) could be regulated by the proteolysis via ubiquitin-proteasome pathway and arsenic sulfide (As4S4) could enhance this process to exert therapeutic effects against CML. However, the exact biochemical mechanism and molecules involved, including the ubiquitin E3 ligases of BCR-ABL, their modification sites and the topologic type of ubiquitination remain uncovered. In this work, by using immunoprecipitation (IP) /2D-nano-HPLC/MALDI-TOF-TOF, we found a number of components in ubiquitination process, such as ubiquitin, E1, E2 and E3 ligases in the BCR-ABL protein complex. Particularly, several E3 ligases including the CBL family E3 ligase c-CBL were identified. The in vitro ubiquitination experiments indicated that c-CBL was one of the E3 ligases of BCR-ABL. Overexpression and knockdown experiments of the c-CBL gene revealed it participated in the process of endogeneous BCR-ABL ubiquitination and turnover. The enforced overexpression of c-CBL could enhance the degradation of BCR-ABL and apoptosis of CML cells whereas the down regulation of c-CBL generated opposite effects. Furthermore, we mapped a domain of c-CBL as the interface to form complex with BCR-ABL based on the protein structure prediction. Either the identification of BCR-ABL ubiquitination sites or the interaction experiment among the c-CBL and BCR-ABL are undergoing. Our data thus suggest that induction of c-CBL may be a new therapeutic approach for CML. Disclosures:No relevant conflicts of interest to declare.