title: Down-regulation of MutS homolog 3 by hypoxia in human colorectal cancer.
abstract: Down-regulation of hMSH3 is associated with elevated microsatellite alterations at selected tetranucleotide repeats and low levels of microsatellite instability in colorectal cancer (CRC). However, the mechanism that down-regulates hMSH3 in CRC is not known. In this study, a significant association between over-expression of glucose transporter 1, a marker for hypoxia, and down-regulation of hMSH3 in CRC tissues was observed. Therefore, we examined the effect of hypoxia on the expression of hMSH3 in human cell lines. When cells with wild type p53 (wt-p53) were exposed to hypoxia, rapid down-regulation of both hMSH2 and hMSH3 occurred. In contrast, when null or mutated p53 (null/mut-p53) cells were exposed to hypoxia, only hMSH3 was down-regulated, and at slower rate than wt-p53 cells. Using a reporter assay, we found that disruption of the two putative hypoxia response elements (HREs) located within the promoter region of the hMSH3 abrogated the suppressive effect of hypoxia on reporter activity regardless of p53 status. In an EMSA, two different forms of HIF-1α complexes that specifically bind to these HREs were detected. A larger complex containing HIF-1α predominantly bound to the HREs in hypoxic null/mut-p53 cells whereas a smaller complex predominated in wt-p53 cells. Finally, HIF-1α knockdown by siRNA significantly inhibited down-regulation of hMSH3 by hypoxia in both wt-p53 and mut-p53 cells. Taken together, our results suggest that the binding of HIF-1α complexes to HRE sites is necessary for down-regulation of hMSH3 in both wt-p53 and mut-p53 cells.
authors.affiliation: Department of Molecular Biology, Toho University School of Medicine, Tokyo, Japan.
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Junichi
authors.initials: J
authors.lastname: Koike
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kugoh
authors.forename: Michitsune
authors.initials: M
authors.lastname: Arita
authors.forename: Takahito
authors.initials: T
authors.lastname: Ohhira
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kikuchi
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Funahashi
authors.forename: Ken
authors.initials: K
authors.lastname: Takamatsu
authors.forename: C Richard
authors.initials: CR
authors.lastname: Boland
authors.forename: Minoru
authors.initials: M
authors.lastname: Koi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Hemmi
mesh_terms: D001483:Base Sequence; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008969:Molecular Sequence Data; D000074081:MutS Homolog 3 Protein; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D020218:Response Elements / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D051272:Glucose Transporter Type 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C078444:MSH3 protein, human; D000074081:MutS Homolog 3 Protein; C495677:SLC2A1 protein, human; D016159:Tumor Suppressor Protein p53