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.
