The role of BH3 proteins in development and disease

Production of cells within an organ is governed by the rates of proliferation, differentiation and death of cells. Apoptosis is the physiological process for deletion of unwanted and potentially harmful cells. Apoptosis is central for modeling tissues during development and for the maintenance of tissue homeostasis. Abnormalities in cell death control can contribute to the development of cancer or autoimmune disease. Under physiological conditions apoptosis is triggered either by ligand-mediated activation of certain members of the tumor necrosis factor receptor (TNF-R) family (e.g. TNF-RI, TRAIL-receptors or CD95/Fas/APO-1) or can be induced by pro-apoptotic members of the Bcl-2 family (e.g. Bim in the case of cytokine withdrawal). Pro-apoptotic members of the Bcl-2 family antagonize the function of pro-survival members of the family and promote the assembly of a signaling complex, the apoptosome, which causes activation of a cascade of cysteine proteases, termed caspases. These enzymes cleave vital cellular proteins and thereby lead to cell collapse. For this return fellowship, I propose to analyze the biological function of two novel pro-apoptotic Bcl-2 family members termed Bmf (Bcl-2 modifying factor) and PUMA/bbc3 (p53 upregulated mediator of apoptosis/Bcl-2 binding component 3), respectively. Bmf was cloned in my current host laboratory as a Bcl-2-binding protein and has all the hallmarks of a pro-apoptotic Bcl-2 protein of the BH3-only subgroup (see below). Bmf is expressed in hemopoietic cells and during early embryogenesis. Our work also demonstrates that Bmf activity is, at least in part, regulated at the posttranslational level. PUMA/bbc3 is also a novel member of the BH3-only subgroup of the Bcl-2 protein family and was cloned simultaneously by different groups as a primary response gene of the tumor suppressor p53. PUMA/bbc3 ideally fits the criteria of a pro-apoptotic Bcl-2 protein of the BH3-only subgroup and is induced in response to a variety of stresses such as g-radiation, cytotoxic drug- or steroid-treatment, as well as serum-withdrawal in a broad range of tissues. I am currently in the process of generating mice that lack bmf or PUMA/bbc3 by targeted deletion of the respective genes. I propose to investigate the function of these novel cell death regulators in normal physiology and in neoplastic disease.