title: Natural and engineered carboxy-terminal variants: decreased secretion and gain-of-function result in asymptomatic coagulation factor VII deficiency.
abstract: We report 2 asymptomatic homozygotes for the nonsense p.R462X mutation affecting the carboxy-terminus of coagulation factor VII (FVII, 466 aminoacids). FVII levels of 3-5% and 2.7 ± 0.4% were found in prothrombin time-based and activated factor X (FXa) generation assays with human thromboplastins. Noticeably, FVII antigen levels were barely detectable (0.7 ± 0.2%) which suggested a gain-of-function effect. This effect was more pronounced with bovine thromboplastin (4.8 ± 0.9%) and disappeared with rabbit thromboplastin (0.7 ± 0.2%). This suggests that the mutation influences tissue factor/FVII interactions. Whereas the recombinant rFVII-462X variant confirmed an increase in specific activity (~400%), a panel of nonsense (p.P466X, p.F465X, p.P464X, p.A463X) and missense (p.R462A, p.R462Q, p.R462W) mutations of the FVII carboxy-terminus resulted in reduced secretion but normal specific activity. These data provide evidence for counteracting pleiotropic effects of the p.R462X mutation, which explains the asymptomatic FVII deficiency, and contributes to our understanding of the role of the highly variable carboxy-terminus of coagulation serine proteases.
authors.affiliation: Dipartimento di Biochimica e Biologia Molecolare and LTTA Centre, Università degli Studi di Ferrara, Ferrara, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Branchini
authors.forename: Lara
authors.initials: L
authors.lastname: Rizzotto
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Mariani
authors.forename: Mariasanta
authors.initials: M
authors.lastname: Napolitano
authors.forename: Mario
authors.initials: M
authors.lastname: Lapecorella
authors.forename: Muriel
authors.initials: M
authors.lastname: Giansily-Blaizot
authors.forename: Rosella
authors.initials: R
authors.lastname: Mari
authors.forename: Alessandro
authors.initials: A
authors.lastname: Canella
authors.forename: Mirko
authors.initials: M
authors.lastname: Pinotti
authors.forename: Francesco
authors.initials: F
authors.lastname: Bernardi
mesh_terms: D000818:Animals; D001777:Blood Coagulation / Q000235:genetics*; D002417:Cattle; D002648:Child; D018389:Codon, Nonsense / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D005167:Factor VII / Q000235:genetics* / Q000378:metabolism*; D005168:Factor VII Deficiency / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D008875:Middle Aged; D016297:Mutagenesis, Site-Directed; D011517:Prothrombin Time; D011817:Rabbits; D013925:Thromboplastin / Q000378:metabolism
chemical_list: D018389:Codon, Nonsense; D005167:Factor VII; D013925:Thromboplastin