ABSTRACT
BH3-only proteins function at a proximal point in a conserved cell death pathway by binding, through their BH3 domains, to other Bcl-2 family members and triggering mitochondrial events associated with apoptosis. Here, we describe a strongly pro-apoptotic BH3-only protein, designated Bbc3, whose expression increases in response to diverse apoptotic stimuli. bbc3 mRNA levels were induced by exposure to DNA-damaging agents and by wild-type p53, which mediates DNA damage-induced apoptosis. p53 transactivated bbc3 through consensus p53 binding sites within the bbc3 promoter region, indicating that bbc3 is a direct target of p53. Additionally, bbc3 mRNA was induced by p53-independent apoptotic stimuli, including dexamethasone treatment of thymocytes, and serum deprivation of tumor cells. Insulin-like growth factor-1 and epidermal growth factor, growth factors with broad anti-apoptotic activity, were each sufficient to suppress Bbc3 expression in serum-starved tumor cells. These results suggest that the transcriptional regulation of bbc3 contributes to the transduction of diverse cell death and survival signals.
Subject(s)
Apoptosis/genetics , Gene Expression Regulation/physiology , Proteins/genetics , Proto-Oncogene Proteins , Signal Transduction/physiology , Tumor Suppressor Protein p53/metabolism , Amino Acid Sequence , Animals , Apoptosis Regulatory Proteins , Base Sequence , Binding Sites , Cell Death , Cell Survival , Cells, Cultured , Consensus Sequence , Fibroblasts/cytology , Fibroblasts/physiology , Genes, p53 , Humans , Leukemia, Myeloid , Mice , Mice, Knockout , Molecular Sequence Data , Open Reading Frames , Polymerase Chain Reaction , Proteins/chemistry , Proteins/metabolism , Sequence Alignment , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Transfection , Tumor Cells, Cultured , Tumor Suppressor Protein p53/geneticsABSTRACT
Regulation of the cell death program involves physical interactions between different members of the Bcl-2 family that either promote or suppress apoptosis. The Bcl-2 homolog, Bak, promotes apoptosis and binds anti-apoptotic family members including Bcl-2 and Bcl-xL. We have identified a domain in Bak that is both necessary and sufficient for cytotoxic activity and binding to Bcl-xL. Sequences similar to this domain were identified in Bax and Bip1, two other proteins that promote apoptosis and interact with Bcl-xL, and were likewise critical for their capacity to kill cells and bind Bcl-xL. Thus, the domain is of central importance in mediating the function of multiple cell death-regulatory proteins that interact with Bcl-2 family members.
Subject(s)
Apoptosis , Conserved Sequence , Membrane Proteins/metabolism , Proto-Oncogene Proteins/metabolism , Amino Acid Sequence , Animals , Apoptosis Regulatory Proteins , Binding Sites , Cell Line , Membrane Proteins/chemistry , Mitochondrial Proteins , Molecular Sequence Data , Protein Binding , Proteins/chemistry , Proto-Oncogene Proteins/chemistry , Proto-Oncogene Proteins c-bcl-2 , Sequence Homology, Amino Acid , bcl-2 Homologous Antagonist-Killer Protein , bcl-2-Associated X Protein , bcl-X ProteinABSTRACT
The survival-promoting activity of the Bcl-2 family of proteins appears to be modulated by interactions between various cellular proteins. We have identified a novel cellular protein, Bik, that interacts with the cellular survival-promoting proteins, Bcl-2 and Bcl-xL, as well as the viral survival-promoting proteins, Epstein Barr virus-BHRF1 and adenovirus E1B-19 kDa. In transient transfection assays, Bik promotes cell death in a manner similar to the death-promoting members of the Bcl-2 family, Bax and Bak. This death-promoting activity of Bik can be suppressed by coexpression of Bcl-2, Bcl-XL, EBV-BHRF1 and E1B-19 kDa proteins suggesting that Bik may be a common target for both cellular and viral anti-apoptotic proteins. While Bik does not show overt homology to the BH1 and BH2 conserved domains characteristic of the Bcl-2 family, it does share a 9 amino acid domain (BH3) with Bax and Bak which may be a critical determinant for the death-promoting activity of these proteins.
