title: Ataxia-telangiectasia: phenotype/genotype studies of ATM protein expression, mutations, and radiosensitivity.
abstract: Previous studies on a limited number of ataxia-telangiectasia (A-T) patients with detectable levels of intracellular ATM protein have suggested a genotype/phenotype correlation. We sought to elucidate this possible correlation by comparing ATM protein levels with mutation types, radiosensitivity, and clinical phenotype. In this study, Western blot analysis was used to measure ATM protein in lysates of lymphoblastoid cell lines (LCLs) from 123 unrelated A-T patients, 10 A-T heterozygotes, and 10 patients with phenotypes similar to A-T. Our Western blot protocol can detect the presence of ATM protein in as little as 1 microg of total protein; at least 25 microg of protein was tested for each individual. ATM protein was absent in 105 of the 123 patients (85%); most of these patients had truncating mutations. The remaining subset of 18 patients (15%) had reduced levels of normal-sized ATM protein; missense mutations were more common in this subset. We used a colony survival assay to characterize the phenotypic response of the LCLs to radiation exposure; patients with or without detectable ATM protein were typically radiosensitive. Nine of 10 A-T heterozygotes also had reduced expression of ATM, indicating that both alleles contribute to ATM protein production. These data suggest that although ATM-specific mRNA is abundant in A-T cells, the abnormal ATM protein is unstable and is quickly targeted for degradation. We found little correlation between level of ATM protein and the type of underlying mutation, the clinical phenotype, or the radiophenotype.
authors.affiliation: Department of Pathology and Laboratory Medicine, UCLA School of Medicine, Los Angeles, California, 90095, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Becker-Catania
authors.forename: G
authors.initials: G
authors.lastname: Chen
authors.forename: M J
authors.initials: MJ
authors.lastname: Hwang
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: X
authors.initials: X
authors.lastname: Sun
authors.forename: O
authors.initials: O
authors.lastname: Sanal
authors.forename: E
authors.initials: E
authors.lastname: Bernatowska-Matuszkiewicz
authors.forename: L
authors.initials: L
authors.lastname: Chessa
authors.forename: E Y
authors.initials: EY
authors.lastname: Lee
authors.forename: R A
authors.initials: RA
authors.lastname: Gatti
mesh_terms: D017668:Age of Onset; D000818:Animals; D001260:Ataxia Telangiectasia / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins; D002472:Cell Transformation, Viral; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins; D015870:Gene Expression; D005838:Genotype; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism / Q000528:radiation effects*; D009154:Mutation; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D011836:Radiation Tolerance; D015996:Survival Rate; D025521:Tumor Suppressor Proteins
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases