title: Factor XII Ofunato: Lys346Asn mutation associated with blood coagulation factor XII deficiency causes impaired secretion through a proteasome-mediated degradation.
abstract: BACKGROUND
  Congenital blood coagulation factor XII (FXII) deficiency is a rare coagulation disease and an autosomal recessive trait. It is found by chance in many cases. We identified a novel mutation (Lys346Asn) in the FXII gene of a patient with FXII deficiency, designated as Factor XII Ofunato.
  
  
  METHODS
  The proband was a 75-year-old Japanese woman with a prolonged activated partial thromboplastin time (52.8s). The FXII activity and antigen were greatly reduced (activity, 5%; antigen, 4.5%). We analyzed FXII gene of this patient using a direct sequencing method and characterized mutant FXII through in vitro expression studies.
  
  
  RESULTS
  Sequence analysis of the FXII gene revealed a G-->C point mutation at nucleotide 9845, resulting in Lys346 (AAG)-->Asn (AAC) replacement in the catalytic domain. Expression studies in Chinese hamster ovary cells demonstrated that mutant FXII (346N-FXII) showed a lower level of accumulation in the cells than wild-type. Secretion of 346N-FXII was greatly reduced in culture medium. We also investigated mRNA expression levels of wild-type and 346N-FXII in transfected cells using quantitative RT-PCR. Both mRNA expressions were equivalent levels. Pulse-chase experiments showed that 346N-FXII was extensively degraded intracellularly compared to wild-type. Using membrane-permeable inhibitors, we observed that degradation occurred in the pre-Golgi compartment and that proteasome apparently plays a central role in this process.
  
  
  CONCLUSIONS
  These results show that most 346N-FXII is degraded intracellularly through endoplasmic reticulum-associated degradation as the protein quality control system, resulting in an insufficient secretion phenotype.
authors.affiliation: Department of Laboratory Medicine, Iwate Medical University School of Medicine, Morioka, Iwate, Japan. ksuzuki-th@umin.ac.jp
authors.forename: Keijiro
authors.initials: K
authors.lastname: Suzuki
authors.forename: Kazunori
authors.initials: K
authors.lastname: Murai
authors.forename: Akira
authors.initials: A
authors.lastname: Suwabe
authors.forename: Yoji
authors.initials: Y
authors.lastname: Ishida
mesh_terms: D000368:Aged; D005175:Factor XII Deficiency / Q000201:enzymology* / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D009154:Mutation; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics*
chemical_list: D046988:Proteasome Endopeptidase Complex