title: MSH3-deficiency initiates EMAST without oncogenic transformation of human colon epithelial cells.
abstract: OBJECTIVE
  Elevated microsatellite instability at selected tetranucleotide repeats (EMAST) is a genetic signature in certain cases of sporadic colorectal cancer and has been linked to MSH3-deficiency. It is currently controversial whether EMAST is associated with oncogenic properties in humans, specifically as cancer development in Msh3-deficient mice is not enhanced. However, a mutator phenotype is different between species as the genetic positions of repetitive sequences are not conserved. Here we studied the molecular effects of human MSH3-deficiency.
  
  
  METHODS
  HCT116 and HCT116+chr3 (both MSH3-deficient) and primary human colon epithelial cells (HCEC, MSH3-wildtype) were stably transfected with an EGFP-based reporter plasmid for the detection of frameshift mutations within an [AAAG]17 repeat. MSH3 was silenced by shRNA and changes in protein expression were analyzed by shotgun proteomics. Colony forming assay was used to determine oncogenic transformation and double strand breaks (DSBs) were assessed by Comet assay.
  
  
  RESULTS
  Despite differential MLH1 expression, both HCT116 and HCT116+chr3 cells displayed comparable high mutation rates (about 4×10(-4)) at [AAAG]17 repeats. Silencing of MSH3 in HCECs leads to a remarkable increased frameshift mutations in [AAAG]17 repeats whereas [CA]13 repeats were less affected. Upon MSH3-silencing, significant changes in the expression of 202 proteins were detected. Pathway analysis revealed overexpression of proteins involved in double strand break repair (MRE11 and RAD50), apoptosis, L1 recycling, and repression of proteins involved in metabolism, tRNA aminoacylation, and gene expression. MSH3-silencing did not induce oncogenic transformation and DSBs increased 2-fold.
  
  
  CONCLUSIONS
  MSH3-deficiency in human colon epithelial cells results in EMAST, formation of DSBs and significant changes of the proteome but lacks oncogenic transformation. Thus, MSH3-deficiency alone is unlikely to drive human colon carcinogenesis.
authors.affiliation: Christian Doppler Laboratory for Molecular Cancer Chemoprevention, Division of Gastroenterology and Hepatology, Department of Medicine 3, Medical University of Vienna, Vienna, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Campregher
authors.forename: Gerald
authors.initials: G
authors.lastname: Schmid
authors.forename: Franziska
authors.initials: F
authors.lastname: Ferk
authors.forename: Siegfried
authors.initials: S
authors.lastname: Knasmüller
authors.forename: Vineeta
authors.initials: V
authors.lastname: Khare
authors.forename: Benedikt
authors.initials: B
authors.lastname: Kortüm
authors.forename: Kyle
authors.initials: K
authors.lastname: Dammann
authors.forename: Michaela
authors.initials: M
authors.lastname: Lang
authors.forename: Theresa
authors.initials: T
authors.lastname: Scharl
authors.forename: Andreas
authors.initials: A
authors.lastname: Spittler
authors.forename: Andres I
authors.initials: AI
authors.lastname: Roig
authors.forename: Jerry W
authors.initials: JW
authors.lastname: Shay
authors.forename: Christopher
authors.initials: C
authors.lastname: Gerner
authors.forename: Christoph
authors.initials: C
authors.lastname: Gasche
mesh_terms: D002460:Cell Line; D003106:Colon / Q000166:cytology / Q000378:metabolism* / Q000473:pathology*; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology*; D053903:DNA Breaks, Double-Stranded; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D053842:Microsatellite Instability; D018895:Microsatellite Repeats / Q000235:genetics*; D000074081:MutS Homolog 3 Protein
chemical_list: D004268:DNA-Binding Proteins; C078444:MSH3 protein, human; D000074081:MutS Homolog 3 Protein