title: Natural mutations lead to enhanced proteasomal degradation of human Ncb5or, a novel flavoheme reductase.
abstract: NADH cytochrome b5 oxidoreductase (Ncb5or) protects β-cells against oxidative stress and lipotoxicity. The predominant phenotype of lean Ncb5or-null mouse is insulin-dependent diabetes due to β-cell death. This suggests the putative role of NCB5OR polymorphism in human diabetes. Therefore, we aimed to investigate the effect of natural missense mutations on the expression of human NCB5OR. Protein and mRNA levels of five non-synonymous coding variants were analyzed in transfected HEK293 and HepG2 cells. Although the mRNA levels were only slightly affected by the mutations, the amount of Ncb5or protein was largely reduced upon two Glu to Gly replacements in the third exon (p.E87G, p.E93G). These two mutations remarkably and synergistically shortened the half-life of Ncb5or and their effect could be attenuated by proteasome inhibitors. Our results strongly indicate that p.E87G, p.E93G mutations lead to enhanced proteasomal degradation due to manifest conformational alterations in the b5 domain. These data provide first evidence for natural mutations in NCB5OR gene resulting in decreased protein levels and hence having potential implications in human pathology.
authors.affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, POB 260, 1444 Budapest, Hungary. kalmanfanni@yahoo.com
authors.forename: Fanni S
authors.initials: FS
authors.lastname: Kálmán
authors.forename: Beáta
authors.initials: B
authors.lastname: Lizák
authors.forename: Szilvia K
authors.initials: SK
authors.lastname: Nagy
authors.forename: Tamás
authors.initials: T
authors.lastname: Mészáros
authors.forename: Veronika
authors.initials: V
authors.lastname: Zámbó
authors.forename: József
authors.initials: J
authors.lastname: Mandl
authors.forename: Miklós
authors.initials: M
authors.lastname: Csala
authors.forename: Eva
authors.initials: E
authors.lastname: Kereszturi
mesh_terms: D042966:Cytochrome-B(5) Reductase / Q000235:genetics* / Q000378:metabolism*; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection
chemical_list: D012333:RNA, Messenger; D042966:Cytochrome-B(5) Reductase; D046988:Proteasome Endopeptidase Complex