Characterization of a novel Bax-associated protein expressed in hemopoietic tissues and regulated during thymocyte apoptosis.

Members of the Bcl-2 protein family have been implicated as critical intracellular regulators of apoptosis. Most studies of this protein family have utilized transformed and/or transfected cell lines expressing high levels of these proteins. In the current study, we have analyzed normal murine lymphoid cells and tissues and have detected a previously unreported protein of approximately 16 kDa recognized by an anti-Bax Ab. This 16-kDa protein is abundant in hemopoietic tissues of both wild-type and Bax knock-out mice, it can heterodimerize with Bax in normal lymphocytes, and it is dramatically down-modulated in thymocytes in response to apoptotic stimuli. These results suggest that this protein may have antiapoptotic activity and may participate in the regulation of apoptosis in normal lymphocytes.