title: Compound heterozygous mutations (p.Leu13Pro and p.Tyr294*) associated with factor VII deficiency cause impaired secretion through ineffective translocation and extensive intracellular degradation of factor VII.
abstract: BACKGROUND
  Congenital coagulation factor VII (FVII) deficiency is a rare coagulation disease. We investigated the molecular mechanisms of this FVII deficiency in a patient with compound heterozygous mutations.
  
  
  METHODS
  A 22-year-old Japanese female was diagnosed with asymptomatic FVII deficiency. The FVII activity and antigen were greatly reduced (activity, 13.0%; antigen, 10.8%). We analyzed the F7 gene of this patient and characterized mutant FVII proteins using in vitro expression studies.
  
  
  RESULTS
  Sequence analysis revealed that the patient was compound heterozygous with a point mutation (p.Leu13Pro) in the central hydrophobic core of the signal peptides and a novel non-sense mutation (p.Tyr294*) in the catalytic domain. Expression studies revealed that mutant FVII with p.Leu13Pro (FVII13P) showed less accumulation in the cells (17.5%) and less secretion into the medium (64.8%) than wild type showed. Truncated FVII resulting from p.Tyr294* (FVII294X) was also decreased in the cells (32.0%), but was not secreted into the medium. Pulse-chase experiments revealed that both mutants were extensively degraded intracellularly compared to wild type. The majority of FVII13P cannot translocate into endoplasmic reticulum (ER). However, a small amount of FVII13P was processed normally with post-translational modifications and was secreted into the medium. The fact that FVII294X was observed only in ER suggests that it is retained in ER. Proteasome apparently plays a central role in these degradations.
  
  
  CONCLUSIONS
  These findings demonstrate that both mutant FVIIs impaired secretion through ineffective translocation to and retention in ER with extensive intracellular degradation, resulting in an insufficient 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: Takeshi
authors.initials: T
authors.lastname: Sugawara
authors.forename: Yoji
authors.initials: Y
authors.lastname: Ishida
authors.forename: Akira
authors.initials: A
authors.lastname: Suwabe
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D005167:Factor VII / Q000378:metabolism*; D005168:Factor VII Deficiency / Q000097:blood* / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D017354:Point Mutation; D011499:Protein Processing, Post-Translational; D014162:Transfection; D055815:Young Adult
chemical_list: D005167:Factor VII