title: The effect of SERPINF1 in-frame mutations in osteogenesis imperfecta type VI.
abstract: Osteogenesis imperfecta type VI is caused by mutations in SERPINF1, which codes for pigment-epithelium derived factor (PEDF). Most of the reported SERPINF1 mutations lead to premature termination codons, but three in-frame insertion or deletion mutations have also been reported. It is not clear how such in-frame mutations lead to OI type VI. In the present study we therefore investigated how SERPINF1 in-frame mutations affect the intracellular localization and secretion of PEDF. Skin fibroblasts affected by SERPINF1 in-frame mutations transcribed SERPINF1 at slightly reduced levels but secretion of PEDF was markedly diminished. Two deletions (p.F277del and the deletion of SERPINF1 exon 5) were associated with retention of PEDF in the endoplasmic reticulum and a stress response in osteoblastic cells. A recurrent in-frame duplication of three amino acids (p.Ala91_Ser93dup) appeared to lead to intracellular degradation but no retention in the endoplasmic reticulum or stress response. Immunofluorescence imaging in transiently transfected osteoblastic MC3T3-E1 cells suggested that PEDF affected by in-frame mutations was not transported along the secretory pathway. MC3T3-E1 osteoblasts stably overexpressing SERPINF1 with the p.Ala91_Ser93dup mutation had decreased collagen type I deposition and mineralization. Thus, the assessed homozygous in-frame deletions or insertions lead to retention or degradation within cellular compartments and thereby interfere with PEDF secretion.
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada.
authors: Hadil
authors: H
authors: Al-Jallad
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada.
authors: Telma
authors: T
authors: Palomo
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada.
authors: Peter
authors: P
authors: Roughley
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada.
authors: Francis H
authors: FH
authors: Glorieux
authors: Faculty of Dentistry, McGill University, Montreal, Quebec, Canada; Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
authors: Marc D
authors: MD
authors: McKee
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada.
authors: Pierre
authors: P
authors: Moffatt
authors: Shriners Hospital for Children and McGill University, Montreal, Quebec, Canada. Electronic address: frauch@shriners.mcgill.ca.
authors: Frank
authors: F
authors: Rauch
mesh_terms: D016475:3T3 Cells; D000293:Adolescent; D000595:Amino Acid Sequence; D000818:Animals; D002648:Child; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D009154:Mutation; D009414:Nerve Growth Factors / Q000737:chemistry / Q000235:genetics*; D010013:Osteogenesis Imperfecta / Q000235:genetics* / Q000473:pathology; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry / Q000235:genetics*; D000099174:Pigment Epithelium-Derived Factor
chemical_list: D005136:Eye Proteins; D009414:Nerve Growth Factors; D015843:Serpins; D000099174:Pigment Epithelium-Derived Factor
keywords: Children; Fractures; Osteoblasts; Osteogenesis imperfecta; Pigment-epithelium derived factor