title: FAS Haploinsufficiency Caused by Extracellular Missense Mutations Underlying Autoimmune Lymphoproliferative Syndrome.
abstract: Mutations in the FAS gene are the most common cause of Autoimmune Lymphoproliferative Syndrome (ALPS), and the majority of them affect the intracellular domain of FAS protein, particularly the region termed death domain. However, approximately one third of these mutations affect the extracellular region of FAS and most are stop codons, with very few missense changes having been described to date. We previously described 7 patients with a FAS missense extracellular mutation, C107Y, two in homozygozity and 5 in heterozygosity. We investigated here the mechanistic effects of this mutation and observed that the homozygous patients did not show any FAS surface expression, while the heterozygous patients had diminished receptor expression. Aiming to understand why a missense mutation was abolishing receptor expression, we analyzed intracellular FAS protein trafficking using fluorescent fusion proteins of wild type FAS, two missense extracellular mutants (FAS-C107Y and FAS-C104Y) and one missense change localized in the intracellular region, FAS-D260E. The FAS-C107Y and FAS-C104Y mutants failed to reach the cell surface, being retained at the endoplasmic reticulum, unlike the WT or the FAS-D260E which were clearly expressed at the plasma membrane. These results support haploinsufficiency as the underlying mechanism involved in the pathogenesis of ALPS caused by extracellular FAS missense mutations.
authors.affiliation: Laboratorio de Biología Molecular Inmunología, Servicio de Inmunología y Reumatología, Hospital de Pediatría S.A.M.I.C. "Prof. Dr. Juan P. Garrahan", Combate de los Pozos N° 1881 (CPA: C 1245 AAM), Ciudad Autónoma de Buenos Aires, República Argentina. gabysimesen@gmail.com.
authors.forename: María Gabriela Simesen
authors.initials: MG
authors.lastname: de Bielke
authors.affiliation: Laboratorio de Inmunología Humoral, Servicio de Inmunología y Reumatología, Hospital de Pediatría S.A.M.I.C. "Prof. Dr. Juan P. Garrahan", Buenos Aires, Argentina.
authors.forename: Laura
authors.initials: L
authors.lastname: Perez
authors.affiliation: Laboratorio de Biología Molecular Inmunología, Servicio de Inmunología y Reumatología, Hospital de Pediatría S.A.M.I.C. "Prof. Dr. Juan P. Garrahan", Combate de los Pozos N° 1881 (CPA: C 1245 AAM), Ciudad Autónoma de Buenos Aires, República Argentina.
authors.forename: Judith
authors.initials: J
authors.lastname: Yancoski
authors.affiliation: Instituto de Medicina Integral Prof. Fernando Figueira-IMIP, Recife, PE, Brazil.
authors.forename: João Bosco
authors.initials: JB
authors.lastname: Oliveira
authors.affiliation: Laboratorio de Biología Molecular Inmunología, Servicio de Inmunología y Reumatología, Hospital de Pediatría S.A.M.I.C. "Prof. Dr. Juan P. Garrahan", Combate de los Pozos N° 1881 (CPA: C 1245 AAM), Ciudad Autónoma de Buenos Aires, República Argentina.
authors.forename: Silvia
authors.initials: S
authors.lastname: Danielian
mesh_terms: D000483:Alleles; D017209:Apoptosis / Q000235:genetics; D001118:Argentina; D056735:Autoimmune Lymphoproliferative Syndrome / Q000235:genetics*; D005110:Extracellular Space; D057809:HEK293 Cells; D057895:Haploinsufficiency; D006801:Humans; D020125:Mutation, Missense / Q000235:genetics*; D010375:Pedigree; D015202:Protein Engineering; D017434:Protein Structure, Tertiary / Q000235:genetics*; D021381:Protein Transport / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics*; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*
chemical_list: C491901:FAS protein, human; D011993:Recombinant Fusion Proteins; D019014:fas Receptor
keywords: ALPS; FAS; apoptosis; haploinsufficiency