Cloning and functional analysis of BAG-1: a novel Bcl-2-binding protein with anti-cell death activity.

Using a protein interaction cloning technique, we identified cDNAs that encode a novel Bcl-2-binding protein, termed BAG-1. The BAG-1 protein shares no significant homology with Bcl-2 or other Bcl-2 family proteins, which can form homo- and heterodimers. In gene transfer experiments using a human lymphoid cell line, Jurkat, coexpression of BAG-1 and Bcl-2 provided markedly increased protection from cell death induced by several stimuli, including staurosporine, anti-Fas antibody, and cytolytic T cells, relative to cells that contained gene transfer-mediated elevations in either BAG-1 or Bcl-2 protein alone. BAG-transfected 3T3 fibroblasts also exhibited prolonged cell survival in response to an apoptotic stimulus. The findings indicate that bag-1 represents a new type of anti-cell death gene and suggest that some routes of apoptosis induction previously ascribed to Bcl-2-independent pathways may instead reflect a need for the combination of Bcl-2 and BAG-1.