1. ¹Department of Translational Cancer Research, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan
2. ²Department of Dental and Medical Biochemistry, Hiroshima University, Hiroshima, Japan
3. ³Department of Molecular Oral Medicine and Maxillofacial Surgery, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan
4. ⁴Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, Sweden
5. ⁵Natural Science Center for Basic Research and Development, Hiroshima University, Hiroshima, Japan
6. ⁶Saitama Medical University International Medical Center, Saitama, Japan

Correspondence: Dr K Tanimoto, Department of Translational Cancer Research, Research Institute for Radiation Biology and Medicine, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan. E-mail: ktanimo@hiroshima-u.ac.jp

Received 4 September 2007; Revised 17 December 2007; Accepted 15 February 2008; Published online 17 March 2008.

Abstract

Tumor hypoxia has been reported to cause a functional loss in DNA mismatch repair (MMR) system as a result of downregulation of MMR genes, although the precise molecular mechanisms remain unclear. In this study, we focused on the downregulation of a key MMR gene, MLH1, and demonstrated that hypoxia-inducible transcription repressors, differentiated embryo chondrocytes (DEC1 and 2), participated in its transcriptional regulation via their bindings to E-box-like motif(s) in MLH1 promoter region. In all cancer cell lines examined, hypoxia increased expression of DEC1 and 2, known as hypoxia-inducible genes, but decreased MLH1 expression in an exposure time-dependent manner at both the mRNA and protein levels. Co-transfection reporter assay revealed that DEC1 and, to greater extent, DEC2 as well as hypoxia-repressed MLH1 promoter activity. We further found that the action was remarkably inhibited by trichostatin A, and identified a possible DEC-response element in the MLH1 promoter. In vitro electrophoretic gel mobility shift and chromatin immunoprecipitation assays demonstrated that DEC1 or 2 directly bounds to the suggested element, and transient transfection assay revealed that overexpression of DEC2 repressed endogenous MLH1 expression in the cells. Hypoxia-induced DEC may impair MMR function through repression of MLH1 expression, possibly via the histone deacethylase-mediated mechanism in cancer cells.