title: Frequent alteration of MLL3 frameshift mutations in microsatellite deficient colorectal cancer.
abstract: BACKGROUND
  MLL3 is a histone 3-lysine 4 methyltransferase with tumor-suppressor properties that belongs to a family of chromatin regulator genes potentially altered in neoplasia. Mutations in MLL3 were found in a whole genome analysis of colorectal cancer but have not been confirmed by a separate study.
  
  
  RESULTS
  We analyzed mutations of coding region and promoter methylation in MLL3 using 126 cases of colorectal cancer. We found two isoforms of MLL3 and DNA sequencing revealed frameshift and other mutations affecting both isoforms of MLL3 in colorectal cancer cells and 19 of 134 (14%) primary colorectal samples analyzed. Moreover, frameshift mutations were more common in cases with microsatellite instability (31%) both in CRC cell lines and primary tumors. The largest isoform of MLL3 is transcribed from a CpG island-associated promoter that has highly homology with a pseudo-gene on chromosome 22 (psiTPTE22). Using an assay which measured both loci simultaneously we found prominent age related methylation in normal colon (from 21% in individuals less than 25 years old to 56% in individuals older than 70, R = 0.88, p<0.001) and frequent hypermethylation (83%) in both CRC cell lines and primary tumors. We next studied the two loci separately and found that age and cancer related methylation was solely a property of the pseudogene CpG island and that the MLL3 loci was unmethylated.
  
  
  CONCLUSIONS
  We found that frameshift mutations of MLL3 in both CRC cells and primary tumor that were more common in cases with microsatellite instability. Moreover, we have shown CpG island-associated promoter of MLL3 gene has no DNA methylation in CRC cells but also primary tumor and normal colon, and this region has a highly homologous of pseudo gene (psiTPTE22) that was age relate DNA methylation.
authors.affiliation: Department of Leukemia, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, United States of America. ponponta@marianna-u.ac.jp
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Castoro
authors.forename: Hyun Soo
authors.initials: HS
authors.lastname: Kim
authors.forename: Brittany
authors.initials: B
authors.lastname: North
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Oikawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hiraishi
authors.forename: Saira S
authors.initials: SS
authors.lastname: Ahmed
authors.forename: Woonbok
authors.initials: W
authors.lastname: Chung
authors.forename: Mee-Yon
authors.initials: MY
authors.lastname: Cho
authors.forename: Minoru
authors.initials: M
authors.lastname: Toyota
authors.forename: Fumio
authors.initials: F
authors.lastname: Itoh
authors.forename: Marcos R H
authors.initials: MR
authors.lastname: Estecio
authors.forename: Lanlan
authors.initials: L
authors.lastname: Shen
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Jelinek
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation / Q000235:genetics; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005260:Female; D016368:Frameshift Mutation / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D015894:Genome, Human / Q000235:genetics; D006801:Humans; D008297:Male; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D008969:Molecular Sequence Data; D015203:Reproducibility of Results
chemical_list: D004268:DNA-Binding Proteins; C452979:KMT2C protein, human