Factor XII Ofunato: Lys346Asn mutation associated with blood coagulation factor XII deficiency causes impaired secretion through a proteasome-mediated degradation.
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.
Suzuki
Keijiro
K
Department of Laboratory Medicine, Iwate Medical University School of Medicine, Morioka, Iwate, Japan. ksuzuki-th@umin.ac.jp
Murai
Kazunori
K
Suwabe
Akira
A
Ishida
Yoji
Y
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*
D046988:Proteasome Endopeptidase Complex