title: FAS haploinsufficiency is a common disease mechanism in the human autoimmune lymphoproliferative syndrome.
abstract: The autoimmune lymphoproliferative syndrome (ALPS) is characterized by early-onset lymphadenopathy, splenomegaly, immune cytopenias, and an increased risk for B cell lymphomas. Most ALPS patients harbor mutations in the FAS gene, which regulates lymphocyte apoptosis. These are commonly missense mutations affecting the intracellular region of the protein and have a dominant-negative effect on the signaling pathway. However, analysis of a large cohort of ALPS patients revealed that ∼30% have mutations affecting the extracellular region of FAS, and among these, 70% are nonsense, splice site, or insertions/deletions with frameshift for which no dominant-negative effect would be expected. We evaluated the latter patients to understand the mechanism(s) by which these mutations disrupted the FAS pathway and resulted in clinical disease. We demonstrated that most extracellular-region FAS mutations induce low FAS expression due to nonsense-mediated RNA decay or protein instability, resulting in defective death-inducing signaling complex formation and impaired apoptosis, although to a lesser extent as compared with intracellular mutations. The apoptosis defect could be corrected by FAS overexpression in vitro. Our findings define haploinsufficiency as a common disease mechanism in ALPS patients with extracellular FAS mutations.
authors.affiliation: Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20814, USA.
authors.forename: Hye Sun
authors.initials: HS
authors.lastname: Kuehn
authors.forename: Iusta
authors.initials: I
authors.lastname: Caminha
authors.forename: Julie E
authors.initials: JE
authors.lastname: Niemela
authors.forename: V Koneti
authors.initials: VK
authors.lastname: Rao
authors.forename: Joie
authors.initials: J
authors.lastname: Davis
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Fleisher
authors.forename: João B
authors.initials: JB
authors.lastname: Oliveira
mesh_terms: D017209:Apoptosis; D056735:Autoimmune Lymphoproliferative Syndrome / Q000235:genetics* / Q000276:immunology / Q000503:physiopathology; D001402:B-Lymphocytes; D002478:Cells, Cultured; D016368:Frameshift Mutation; D057895:Haploinsufficiency; D006801:Humans; D020125:Mutation, Missense; D016133:Polymerase Chain Reaction; D020871:RNA Stability; D015398:Signal Transduction; D019014:fas Receptor / Q000235:genetics* / Q000502:physiology
chemical_list: C491901:FAS protein, human; D019014:fas Receptor