Arsenic Sulfide Binds c-CBL to Promote BCR-ABL Ubiquitination and Degradation In Chronic Myelogenous Leukemia.

Abstract 1200

Using immunoprecipitation (IP)-2D-nano-HPLC-MALDI-MS-MS, we identified c-CBL in association with BCR-ABL in a multi-protein complex in K562 cells. In vitro ubiquitination and mutagenesis analyses show that c-CBL serves as a specific E3 ligase for ubiquitination of BCR-ABL at K1517. Arsenic sulfide (As₄S₄) treatment results in increased c-CBL protein level, which promotes ubiquitination and subsequent degradation of BCR-ABL and apoptosis of K562 cells. Elevated c-CBL is necessary and sufficient to recapitulate the effect of As₄S_4. Interestingly, arsenic directly binds the RING finger domain of c-CBL, inhibiting its self-ubiquitination and degradation, thus leading to accumulation of c-CBL. However, this interaction between As₄S₄ and c-CBL does not interfere with its E3 ligase activity towards BCR-ABL. Increased c-CBL protein and BCR-ABL degradation are also observed in vivo after As₄S₄ administration in BCR-ABL leukemia mice. These findings provide insights into the molecular mechanisms of arsenic and its potential therapeutic applications in CML.