title: Heme-binding protein HRG-1 is induced by insulin-like growth factor I and associates with the vacuolar H+-ATPase to control endosomal pH and receptor trafficking.
abstract: Endocytosis and trafficking of receptors and nutrient transporters are dependent on an acidic intra-endosomal pH that is maintained by the vacuolar H(+)-ATPase (V-ATPase) proton pump. V-ATPase activity has also been associated with cancer invasiveness. Here, we report on a new V-ATPase-associated protein, which we identified in insulin-like growth factor I (IGF-I) receptor-transformed cells, and which was separately identified in Caenorhabditis elegans as HRG-1, a member of a family of heme-regulated genes. We found that HRG-1 is present in endosomes but not in lysosomes, and it is trafficked to the plasma membrane upon nutrient withdrawal in mammalian cells. Suppression of HRG-1 with small interfering RNA causes impaired endocytosis of transferrin receptor, decreased cell motility, and decreased viability of HeLa cells. HRG-1 interacts with the c subunit of the V-ATPase and enhances V-ATPase activity in isolated yeast vacuoles. Endosomal acidity and V-ATPase assembly are decreased in cells with suppressed HRG-1, whereas transferrin receptor endocytosis is enhanced in cells that overexpress HRG-1. Cellular uptake of a fluorescent heme analogue is enhanced by HRG-1 in a V-ATPase-dependent manner. Our findings indicate that HRG-1 regulates V-ATPase activity, which is essential for endosomal acidification, heme binding, and receptor trafficking in mammalian cells. Thus, HRG-1 may facilitate tumor growth and cancer progression.
authors.affiliation: Cell Biology Laboratory, Department of Biochemistry, BioSciences Institute, University College Cork, Cork, Ireland.
authors.forename: Katie M
authors.initials: KM
authors.lastname: O'Callaghan
authors.forename: Veronica
authors.initials: V
authors.lastname: Ayllon
authors.forename: Jean
authors.initials: J
authors.lastname: O'Keeffe
authors.forename: Yanru
authors.initials: Y
authors.lastname: Wang
authors.forename: Orla T
authors.initials: OT
authors.lastname: Cox
authors.forename: Gary
authors.initials: G
authors.lastname: Loughran
authors.forename: Michael
authors.initials: M
authors.lastname: Forgac
authors.forename: Rosemary
authors.initials: R
authors.lastname: O'Connor
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects* / Q000201:enzymology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006420:Hemeproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011990:Receptors, Transferrin / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: C546603:HRG-1 protein, mouse; D006420:Hemeproteins; D012333:RNA, Messenger; D011990:Receptors, Transferrin; C546602:SLC48A1 protein, human; D007334:Insulin-Like Growth Factor I; D025262:Vacuolar Proton-Translocating ATPases