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

Abstract 3257

Poster Board III-1

We 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.