title: Stepwise deletions of polyA sequences in mismatch repair-deficient colorectal cancers.
abstract: PolyA simple repeat sequence deletions are common in tumors with microsatellite instability (MSI+). Such deletions occur one base at a time in DNA mismatch repair (MMR)-deficient yeast suggesting larger deletions in human MSI+ tumors represent multiple sequential stepwise losses. Sum total deletions in four polyA repeats were variable (between -17 to -45 bp) in 20 sporadic MSI+ colorectal cancers. Progressive but less extensive total deletions (maximum of -12 bp) occurred in similar polyA sequences in MMR-deficient mice (mlh1-/-) up to 478 days old. PolyA repeat lengths were relatively stable but already shortened in the MMR-deficient cell line HCT116. A transgene with 26 A's transfected into HCT116 shortened an average of 3.8 bases pairs after 469 days in culture, less than average deletions of BAT25 (-5.3) or BAT26 (-9.0) in MSI+ cancers. These findings further suggest that extensive polyA deletions common in MSI+ tumors likely reflect multiple stepwise smaller deletions that accumulate more than hundreds of divisions after loss of MMR.
authors.affiliation: Department of Pathology, University of Southern California School of Medicine, Los Angeles, California, USA.
authors.forename: C
authors.initials: C
authors.lastname: Blake
authors.forename: J L
authors.initials: JL
authors.lastname: Tsao
authors.forename: A
authors.initials: A
authors.lastname: Wu
authors.forename: D
authors.initials: D
authors.lastname: Shibata
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D020137:Base Pair Mismatch / Q000235:genetics; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004252:DNA Mutational Analysis; D004260:DNA Repair; D019073:HT29 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D018895:Microsatellite Repeats / Q000235:genetics; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009363:Neoplasm Proteins / Q000172:deficiency* / Q000235:genetics; D009687:Nuclear Proteins; D011061:Poly A / Q000235:genetics*; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501486:MLH1 protein, human; C501485:Mlh1 protein, mouse; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011061:Poly A; D004247:DNA; D000070957:MutL Protein Homolog 1