title: The nucleotide composition of microsatellites impacts both replication fidelity and mismatch repair in human colorectal cells.
abstract: Microsatellite instability is a key mechanism of colon carcinogenesis. We have previously studied mutations within a (CA)13 microsatellite using an enhanced green fluorescent protein (EGFP)-based reporter assay that allows the distinction of replication errors and mismatch repair (MMR) activity. Here we utilize this assay to compare mutations of mono- and dinucleotide repeats in human colorectal cells. HCT116 and HCT116+chr3 cells were stably transfected with EGFP-based plasmids harboring A10, G10, G16, (CA)13 and (CA)26 repeats. EGFP-positive mutant fractions were quantitated by flow cytometry, mutation rates were calculated and the mutant spectrum was analyzed by cycle sequencing. EGFP fluorescence pattern changed with the microsatellite's nucleotide sequence and cell type and clonal variations were observed in mononucleotide repeats. Replication errors (as calculated in HCT116) at A10 repeats were 5-10-fold higher than in G10, G16 were 30-fold higher than G10 and (CA)26 were 10-fold higher than (CA)13. The mutation rates in hMLH1-proficient HCT116+chr3 were 30-230-fold lower than in HCT116. MMR was more efficient in G16 than in A10 clones leading to a higher stability of poly-G tracts. Mutation spectra revealed predominantly 1-unit deletions in A10, (CA)13 and G10 and 2-unit deletions or 1-unit insertion in (CA)26. These findings indicate that both replication fidelity and MMR are affected by the microsatellite's nucleotide composition.
authors.affiliation: Department of Medicine 3, Medical University of Vienna, Vienna, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Campregher
authors.forename: Theresa
authors.initials: T
authors.lastname: Scharl
authors.forename: Manuela
authors.initials: M
authors.lastname: Nemeth
authors.forename: Clemens
authors.initials: C
authors.lastname: Honeder
authors.forename: Thomas
authors.initials: T
authors.lastname: Jascur
authors.forename: C Richard
authors.initials: CR
authors.lastname: Boland
authors.forename: Christoph
authors.initials: C
authors.lastname: Gasche
mesh_terms: D001483:Base Sequence; D002893:Chromosomes, Human, Pair 3; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism; D053843:DNA Mismatch Repair; D004261:DNA Replication / Q000235:genetics; D018900:Dinucleotide Repeats; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins; D045325:HCT116 Cells; D006801:Humans; D018895:Microsatellite Repeats / Q000235:genetics*; D009154:Mutation; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured
chemical_list: D049452:Green Fluorescent Proteins