Proapoptotic BH3-Only Proteins Trigger Membrane Integration of Prosurvival Bcl-w and Neutralize Its Activity

• Published in: The Journal of cell biology Vol. 162; no. 5; pp. 877 - 887
• Main Authors: Wilson-Annan, Julie, O'Reilly, Lorraine A., Crawford, Simon A., Hausmann, George, Beaumont, Jennifer G., Parma, Loes P., Chen, Lin, Lackmann, Martin, Lithgow, Trevor, Hinds, Mark G., Day, Catherine L., Adams, Jerry M., David C. S. Huang
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 01-09-2003; The Rockefeller University Press
• Subjects: Animals; Apoptosis; Apoptosis - physiology; Apoptosis Regulatory Proteins; Cell death; Cell division; Cell Fractionation; Cell lines; Cell Membrane - metabolism; Cell Survival - physiology; Cells; Cellular immunity; Chimeras; Fractionation; HeLa Cells; Humans; Membrane Potentials - physiology; Membrane Proteins - genetics; Membrane Proteins - metabolism; Membranes; Mitochondria; Mitochondria - metabolism; Mitochondria - ultrastructure; Mitochondrial Proteins - metabolism; P branes; Peptide Fragments - genetics; Peptide Fragments - metabolism; Protein Binding; Proteins; Proteins - genetics; Proteins - metabolism; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rats; Recombinant Fusion Proteins - metabolism
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200302144

Prosurvival Bcl-2-like proteins, like Bcl-w, are thought to function on organelles such as the mitochondrion and to be targeted to them by their hydrophobic COOH-terminal domain. We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis. In healthy cells, Bcl-w was loosely attached to the mitochondrial membrane, but it was converted into an integral membrane protein by cytotoxic signals that induce binding of BH3-only proteins, such as Bim, or by the addition of BH3 peptides to lysates. As the structure of Bcl-w has revealed that its COOH-terminal domain occupies the hydrophobic groove where BH3 ligands bind, displacement of that domain by a BH3 ligand would displace the hydrophobic COOH-terminal residues, allowing their insertion into the membrane. To determine whether BH3 ligation is sufficient to induce the enhanced membrane affinity, or to render Bcl-w proapoptotic, we mimicked their complex by tethering the Bim BH3 domain to the NH2 terminus of Bcl-w. The chimera indeed bound avidly to membranes, in a fashion requiring the COOH-terminal domain, but neither promoted nor inhibited apoptosis. These results suggest that ligation of a proapoptotic BH3-only protein alters the conformation of Bcl-w, enhances membrane association, and neutralizes its survival function.