title: The precursor to the germ cell-specific PCSK4 proteinase is inefficiently activated in transfected somatic cells: evidence of interaction with the BiP chaperone.
abstract: Proprotein convertase subtilisin/kexin type 4 (PCSK4), also known as proprotein convertase 4 (PC4), is a serine endoproteinase primarily expressed in testicular germ cells and in sperm. Inactivation of its gene in mouse causes male infertility. From studies of the biosynthesis of PCSK3/furin, its closest relative, it has been inferred that PCSK4 is synthesised in the endoplasmic reticulum as a zymogen; that it is rapidly matured by autocatalytic cleavage between the prodomain and the catalytic domain; that the cleaved prodomain remains attached to the mature enzyme; and that the enzyme is finally activated by the removal of the prodomain peptides following a secondary cleavage within the prodomain. In this study, we used human embryonic kidney 293 (HEK293) cells to study the biosynthesis of rat or human PCSK4. Our results show that the bulk of PCSK4 remains as an intracellular zymogen, presumably trapped in the endoplasmic reticulum, where it interacts with the general molecular chaperone glucose-regulated protein 78/Immunoglobulin heavy-chain binding protein (GRP78/BiP). These data suggest that, unlike other members of the convertase family, proPCSK4 cannot efficiently self-activate in somatic cells. These cells may lack the intracellular environment and the interacting molecules specific to testicular germ cells where this enzyme is normally expressed.
authors.affiliation: Chronic Disease Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: Gyamera-Acheampong
authors.forename: Francine
authors.initials: F
authors.lastname: Sirois
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Denis
authors.forename: Priyambada
authors.initials: P
authors.lastname: Mishra
authors.forename: Daniel
authors.initials: D
authors.lastname: Figeys
authors.forename: Ajoy
authors.initials: A
authors.lastname: Basak
authors.forename: Majambu
authors.initials: M
authors.lastname: Mbikay
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D043484:Proprotein Convertases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D051381:Rats; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013094:Spermatozoa / Q000201:enzymology; D013381:Subtilisins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D004792:Enzyme Precursors; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; C489716:PCSK4 protein, human; C489717:Pcsk4 protein, mouse; C078312:Pcsk4 protein, rat; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D013381:Subtilisins