title: 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.
abstract: 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.
authors.affiliation: Urologic Laboratory, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: J
authors.initials: J
authors.lastname: Lin
authors.forename: L
authors.initials: L
authors.lastname: Hutchinson
authors.forename: S M
authors.initials: SM
authors.lastname: Gaston
authors.forename: G
authors.initials: G
authors.lastname: Raab
authors.forename: M R
authors.initials: MR
authors.lastname: Freeman
mesh_terms: D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D016466:CHO Cells; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism*; D002470:Cell Survival; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques; D014452:Ubiquitins / Q000378:metabolism
chemical_list: C091732:BCL2-associated athanogene 1 protein; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D014452:Ubiquitins; D004815:Epidermal Growth Factor; D005047:Etoposide; D006493:Heparin; D005982:Glutathione Transferase