title: Impaired suppressive activities of human MUTYH variant proteins against oxidative mutagenesis.
abstract: OBJECTIVE
  To investigate the suppressive activity of MUTYH variant proteins against mutations caused by oxidative lesion, 8-hydroxyguanine (8OHG), in human cells.
  
  
  METHODS
  p.R154H, p.M255V, p.L360P, and p.P377L MUTYH variants, which were previously found in patients with colorectal polyposis and cancer, were selected for use in this study. Human H1299 cancer cell lines inducibly expressing wild-type (WT) MUTYH (type 2) or one of the 4 above-mentioned MUTYH variants were established using the piggyBac transposon vector system, enabling the genomic integration of the transposon sequence for MUTYH expression. MUTYH expression was examined after cumate induction using Western blotting analysis and immunofluorescence analysis. The intracellular localization of MUTYH variants tagged with FLAG was also immunofluorescently examined. Next, the mutation frequency in the supF of the shuttle plasmid pMY189 containing a single 8OHG residue at position 159 of the supF was compared between empty vector cells and cells expressing WT MUTYH or one of the 4 MUTYH variants using a supF forward mutation assay.
  
  
  RESULTS
  The successful establishment of human cell lines inducibly expressing WT MUTYH or one of the 4 MUTYH variants was concluded based on the detection of MUTYH expression in these cell lines after treatment with cumate. All of the MUTYH variants and WT MUTYH were localized in the nucleus, and nuclear localization was also observed for FLAG-tagged MUTYH. The mutation frequency of supF was 2.2 × 10(-2) in the 8OHG-containing pMY189 plasmid and 2.5 × 10(-4) in WT pMY189 in empty vector cells, which was an 86-fold increase with the introduction of 8OHG. The mutation frequency (4.7 × 10(-3)) of supF in the 8OHG-containing pMY189 plasmid in cells overexpressing WT MUTYH was significantly lower than in the empty vector cells (P < 0.01). However, the mutation frequencies of the supF in the 8OHG-containing pMY189 plasmid in cells overexpressing the p.R154H, p.M255V, p.L360P, or p.P377L MUTYH variant were 1.84 × 10(-2), 1.55 × 10(-2), 1.91 × 10(-2), and 1.96 × 10(-2), respectively, meaning that no significant difference was observed in the mutation frequency between the empty vector cells and cells overexpressing MUTYH mutants.
  
  
  CONCLUSIONS
  The suppressive activities of p.R154H, p.M255V, p.L360P, and p.P377L MUTYH variants against mutations caused by 8OHG are thought to be severely impaired in human cells.
authors: Department of Tumor Pathology, Hamamatsu University School of Medicine, Shizuoka 431-3192, Japan. kzshinmu@hama-med.ac.jp
authors: Kazuya
authors: K
authors: Shinmura
authors: Masanori
authors: M
authors: Goto
authors: Hong
authors: H
authors: Tao
authors: Shun
authors: S
authors: Matsuura
authors: Tomonari
authors: T
authors: Matsuda
authors: Haruhiko
authors: H
authors: Sugimura
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000235:genetics; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics; D045647:DNA Glycosylases / Q000235:genetics*; D004260:DNA Repair; D019084:Fluorescent Antibody Technique, Indirect; D014644:Genetic Variation; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D016296:Mutagenesis; D009154:Mutation; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism
chemical_list: C024829:8-hydroxyguanine; D006147:Guanine; D045647:DNA Glycosylases; C061738:mutY adenine glycosylase; D010100:Oxygen
keywords: 8-hydroxyguanine; Colorectal polyposis; MUTYH; MUTYH-associated polyposis; Mutation; Oxidative mutagenesis; piggyBac transposon; supF forward mutation assay