1. ¹Center for Advanced Biotechnology and Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854-5638, USA
2. ²Graduate Program in Biochemistry and Molecular Biology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854-5638, USA
3. ³Department of Pathology and Internal Medicine, University of Michigan, Ann Arbor, MI 48109-0602, USA
4. ⁴Department of Biochemistry and Cancer Institute of New Jersey, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854-5638, USA
5. ⁵Present address: CRBM-CNRS FRE 2593, 1919 Route de Mende, F-34293 Montpellier, France

Correspondence: C Gélinas, CABM and Department of Biochemistry, UMDNJ – Robert Wood Johnson Medical School, 679 Hoes Lane, Piscataway, NJ 08854-5638, USA. Tel: 732 235 5035; Fax: 732 235 4466; E-mail: gelinas@cabm.rutgers.edu

Received 15 November 2004; Revised 11 April 2005; Accepted 28 April 2005; Published online 17 June 2005.

Abstract

Bfl-1/A1 is generally recognized as a Bcl-2-related inhibitor of apoptosis. We show that Bfl-1 undergoes constitutive ubiquitin/proteasome-mediated turnover. Moreover, while Bfl-1 suppresses apoptosis induced by staurosporine or cytokine withdrawal, it is proapoptotic in response to tumor necrosis factor (TNF) receptor activation in FL5.12 pro-B cells. Its anti- versus proapoptotic effect is regulated by two proteolytic events: (1) its constitutive proteasome-mediated turnover and (2) its TNF/cycloheximide (CHX)-induced cleavage by -calpain, or a calpain-like activity, coincident with acquisition of a proapoptotic phenotype. In vitro studies suggest that calpain-mediated cleavage of Bfl-1 occurs between its Bcl-2 homology (BH)4 and BH3 domains. This would be consistent with the generation of a proapoptotic Bax-like BH1–3 molecule. Overall, our studies uncovered two new regulatory mechanisms that play a decisive role in determining Bfl-1's prosurvival versus prodeath activities. These findings might provide important clues to counteract chemoresistance in tumor cells that highly express Bfl-1.