title: Mutation frequency in coding and non-coding repeat sequences in mismatch repair deficient cells derived from normal human tissue.
abstract: Repetitive tracts within the coding regions of TGFBR2 and BAX are frequently mutated in mismatch repair deficient tumours and are implicated in tumour progression. However, there has been little study of the balance between selection pressure and inherent instability at sequences within these genes. To determine whether TGFBR2 and BAX are inherently prone to mutations in the presence of MMR defects, we studied MMR deficient cells derived from B-lymphocytes. By analysing cells derived from normal tissue we aimed to minimize the effects of selection pressures that bias the apparent frequency of mutation. We definitively show that certain sequences, usually repaired by MMR, are inherently unstable. Using a small pool PCR technique we confirmed these cells exhibit microsatellite instability. Additionally, we demonstrate that MMR deficiency results in an excess of mutations, specifically at the poly(A)(10) tract compared to other regions of the TGFBR2 gene (P<0.001). Conversely, an excess of mutations does not appear to arise at the poly(G)(8) tract of the BAX gene. These studies provide insight into the mechanism by which TGFBR2 and BAX genes become mutated during tumorigenesis. These findings invoke the notion of "unmasking" specific hypermutable sequences in particular genes adding further complexity to the concept of the mutator phenotype.
authors.affiliation: Department of Oncology and MRC Human Genetics Unit, Western General Hospital, University of Edinburgh, Crewe Road, Edinburgh, EH4 2XU, UK.
authors.forename: A L
authors.initials: AL
authors.lastname: Bacon
authors.forename: S M
authors.initials: SM
authors.lastname: Farrington
authors.forename: M G
authors.initials: MG
authors.lastname: Dunlop
mesh_terms: D000483:Alleles; D020137:Base Pair Mismatch; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004260:DNA Repair; D004262:DNA Restriction Enzymes / Q000378:metabolism; D005091:Exons; D005434:Flow Cytometry; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism; D018895:Microsatellite Repeats / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D011061:Poly A; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid; D051028:bcl-2-Associated X Protein
chemical_list: C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D018125:Receptors, Transforming Growth Factor beta; D051028:bcl-2-Associated X Protein; D011061:Poly A; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D004262:DNA Restriction Enzymes