BAG-1 is a novel cytoplasmic binding partner of the membrane form of heparin-binding EGF-like growth factor: a unique role for proHB-EGF in cell survival regulation

• Published in: The Journal of biological chemistry 2001-08, Vol.276 (32), p.30127
• Main Authors: Lin, J, Hutchinson, L, Gaston, S M, Raab, G, Freeman, M R
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Binding Sites; Carrier Proteins - chemistry; Carrier Proteins - metabolism; Cell Adhesion - drug effects; Cell Division; Cell Membrane - metabolism; Cell Survival; CHO Cells; COS Cells; Cricetinae; Cytoplasm - metabolism; DNA-Binding Proteins; Dose-Response Relationship, Drug; Epidermal Growth Factor - metabolism; Etoposide - pharmacology; Glutathione Transferase - metabolism; Heparin - metabolism; HSP70 Heat-Shock Proteins - metabolism; Humans; Microscopy, Confocal; Nucleic Acid Synthesis Inhibitors - pharmacology; Protein Binding; Protein Isoforms; Protein Structure, Tertiary; Recombinant Fusion Proteins - metabolism; Time Factors; Transcription Factors; Transfection; Tumor Cells, Cultured; Two-Hybrid System Techniques; Ubiquitins - metabolism
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M010237200

Several cell functions related to growth and survival regulation have been attributed specifically to the membrane form of heparin-binding EGF-like growth factor (proHB-EGF), rather than to the diffusible, processed HB-EGF isoform. These findings suggest the existence of a functional binding partner specifically for the membrane form of the growth factor. In this study we have identified the prosurvival cochaperone, BAG-1, as a protein that interacts with the cytoplasmic tail domain of proHB-EGF. Interaction between BAG-1 and the 24-amino acid proHB-EGF cytoplasmic tail was initially identified in a yeast two-hybrid screen and was confirmed in mammalian cells. The proHB-EGF tail bound BAG-1 in an hsp70-independent manner and within a 97-amino acid segment that includes the ubiquitin homology domain in BAG-1 but does not include the hsp70 binding site. Effects of BAG-1 and proHB-EGF co-expression were demonstrated in cell adhesion and cell survival assays and in quantitative assays of regulated secretion of soluble HB-EGF. Because the BAG-1 binding site is not present on the mature, diffusible form of the growth factor, these findings suggest a new mechanism by which proHB-EGF, in isolation from the diffusible form, can mediate cell signaling events. In addition, because effects of BAG-1 on regulated secretion of soluble HB-EGF were also identified, this interaction has the potential to alter the signaling capabilities of both the membrane-anchored and the diffusible forms of the growth factor.