1. ¹Center for Advanced Biotechnology and Medicine, UMDNJ—Robert Wood Johnson Medical School, Piscataway, NJ, USA
2. ²Graduate Program in Biochemistry and Molecular Biology, UMDNJ—Robert Wood Johnson Medical School, Piscataway, NJ, USA
3. ³Department of Molecular Biology and Biochemistry, Rutgers University, New Brunswick, NJ, USA
4. ⁴Cancer Institute of New Jersey, New Brunswick, NJ, USA
5. ⁵Department of Biochemistry, UMDNJ—Robert Wood Johnson Medical School, Piscataway, NJ, USA

Correspondence: Dr C Gélinas, CABM and Department of Biochemistry, Robert Wood Johnson Medical School, CABM, room 137, 679 Hoes Lane, Piscataway, NJ 08854-5638, USA. E-mail: gelinas@cabm.rutgers.edu

⁶Present address: Department of Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01650, USA.

⁷Present address: Department of Molecular Genetics and Microbiology, SUNY-Stony Brook, Stony Brook, NY 11794-5222, USA.

Received 21 March 2007; Revised 23 July 2007; Accepted 3 August 2007; Published online 3 September 2007.

Abstract

The prosurvival Bcl-2-family member Bfl-1/A1 is a transcriptional target of nuclear factor-B (NF-B) that is overexpressed in many human tumors and is a means by which NF-B inhibits apoptosis, but its mode of action is controversial. To better understand how Bfl-1 functions, we investigated its interaction with proapoptotic multidomain proteins Bax and Bak, and the BH3-only proteins Bid and tBid. We demonstrate that in living cells Bfl-1 selectively interacts with Bak and tBid, but not with Bax or Bid. Bfl-1/Bak interaction is functional as Bfl-1 suppressed staurosporine (STS)-induced apoptosis in wild-type and Bax-deficient cells, but not in Bak-/- cells. We also show that Bfl-1 blocks tumor necrosis factor- (TNF)-induced activation of Bax indirectly, via association with tBid. C-terminal deletion decreased Bfl-1's interaction with Bak and tBid and reduced its ability to suppress Bak- and tBid-mediated cell death. These data indicate that Bfl-1 utilizes different mechanisms to suppress apoptosis depending on the stimulus. Bfl-1 associates with tBid to prevent activation of proapoptotic Bax and Bak, and it also interacts directly with Bak to antagonize Bak-mediated cell death, similar to Mcl-1. Thus, part of the protective function of NF-B is to induce Mcl-1-like activity by upregulating Bfl-1.