CHARACTERIZATION OF A NOVEL BAX-ASSOCIATED PROTEIN EXPRESSED IN HEMATOPOIETIC TISSUES AND REGULATED DURING THYMOCYTE APOPTOSIS

Members of the Bcl-2 protein family have been implicated as critical i ntracellular regulators of apoptosis. Most studies of this protein fam ily 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 previous ly unreported protein of approximately 16 kDa recognized by an anti-Ba r Ab. This 16-kDa protein is abundant in hemopoietic tissues of both w ild-type and Bax knock-out mice, it can heterodimerize,vith Bar in nor mal lymphocytes, and it is dramatically down-modulated in thymocytes i n response to apoptotic stimuli. These results suggest that this prote in may have antiapoptotic activity and may participate in the regulati on of apoptosis in normal lymphocytes.