title: Apoptosis-inducing signal sequence mutation in carbonic anhydrase IV identified in patients with the RP17 form of retinitis pigmentosa.
abstract: Genetic and physical mapping of the RP17 locus on 17q identified a 3.6-megabase candidate region that includes the gene encoding carbonic anhydrase IV (CA4), a glycosylphosphatidylinositol-anchored protein that is highly expressed in the choriocapillaris of the human eye. By sequencing candidate genes in this region, we identified a mutation that causes replacement of an arginine with a tryptophan (R14W) in the signal sequence of the CA4 gene at position -5 relative to the signal sequence cleavage site. This mutation was found to cosegregate with the disease phenotype in two large families and was not found in 36 unaffected family members or 100 controls. Expression of the mutant cDNA in COS-7 cells produced several findings, suggesting a mechanism by which the mutation can explain the autosomal dominant disease. In transfected COS-7 cells, the R14W mutation (i) reduced the steady-state level of carbonic anhydrase IV activity expressed by 28% due to a combination of decreased synthesis and accelerated turnover; (ii) led to up-regulation of immunoglobulin-binding protein, double-stranded RNA-regulated protein kinase-like ER kinase, and CCAAT/enhancer-binding protein homologous protein, markers of the unfolded protein response and endoplasmic reticulum stress; and (iii) induced apoptosis, as evidenced by annexin V binding and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling staining, in most cells expressing the mutant, but not the WT, protein. We suggest that a high level of expression of the mutant allele in the endothelial cells of the choriocapillaris leads to apoptosis, leading in turn to ischemia in the overlying retina and producing autosomal dominant retinitis pigmentosa.
authors.affiliation: Medical Research Council Human Genetics Research Unit, Division of Human Genetics, Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Observatory, Cape Town 7925, South Africa.
authors.forename: George
authors.initials: G
authors.lastname: Rebello
authors.forename: Rajkumar
authors.initials: R
authors.lastname: Ramesar
authors.forename: Alvera
authors.initials: A
authors.lastname: Vorster
authors.forename: Lisa
authors.initials: L
authors.lastname: Roberts
authors.forename: Liezle
authors.initials: L
authors.lastname: Ehrenreich
authors.forename: Ekow
authors.initials: E
authors.lastname: Oppon
authors.forename: Dumisani
authors.initials: D
authors.lastname: Gama
authors.forename: Soraya
authors.initials: S
authors.lastname: Bardien
authors.forename: Jacquie
authors.initials: J
authors.lastname: Greenberg
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bonapace
authors.forename: Abdul
authors.initials: A
authors.lastname: Waheed
authors.forename: Gul N
authors.initials: GN
authors.lastname: Shah
authors.forename: William S
authors.initials: WS
authors.lastname: Sly
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D015153:Blotting, Western; D019556:COS Cells; D030741:Carbonic Anhydrase IV / Q000235:genetics*; D002886:Chromosomes, Human, Pair 17; D004591:Electrophoresis, Polyacrylamide Gel; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007150:Immunohistochemistry; D009154:Mutation; D012174:Retinitis Pigmentosa / Q000201:enzymology / Q000235:genetics*; D015854:Up-Regulation
chemical_list: D030741:Carbonic Anhydrase IV