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.
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.
O'Callaghan
Katie M
KM
Cell Biology Laboratory, Department of Biochemistry, BioSciences Institute, University College Cork, Cork, Ireland.
Ayllon
Veronica
V
O'Keeffe
Jean
J
Wang
Yanru
Y
Cox
Orla T
OT
Loughran
Gary
G
Forgac
Michael
M
O'Connor
Rosemary
R
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*
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