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(PP359) A new role of MEPE/OF45 as a co-factor of CHK1 in DNA damage response.
Wang, Ya*,1, Hu, Baocheng1, 2, Liu, Shuang2, Wang, Xiang1, Rowe, Peter 3, Huang, Cuifen 2, 1 Radiation Oncology, Philadelphia, PA, USA2 Molecular Biology, Beijing, China, China3 Periodontics, San Antonio, TX, USA
ABSTRACT- Matrix extracellular phosphoglycoprotein/osteoblast/osteocyte factor 45 (MEPE/OF45) was first identified in human bone marrow as well as human tumor-induced osteomalacia and in rat bone marrow derived osteoblasts in 2000. Soon, the murine homologue of MEPE/OF45 was reported the following year. Since MEPE/OF45 was identified, its function related to bone metabolism have been widely investigated. However, we report here a new role of MEPE/OF45 as a co-factor of CHK1 in DNA damage response. CHK1 is one of the most important components of the DNA damage response. In actively dividing cells, the regulation of CHK1 in mammalian cells is cell cycle dependent, indicating that CHK1 is an actively degraded protein. Several lines of evidence suggest that CHK1 degradation is involved in ubiquitination. But, the underlying mechanism related to CHK1 ubiquitination is far from being understood. We previously reported that one rat transformed embryo fibroblast cell line, A1-5, is much more resistant to ionizing radiation (IR) or camptothecin (CPT) than its counterpart, B4 cell line. We also demonstrated that the resistance of A-1 cells to DNA damage inducers is because of higher levels of CHK1 in A1-5 cells than in B4 cells. To look for co-factor of CHK1 in A1-5 cells, we used PCR-select cDNA subtraction method to identify genes differentially expressed between these two cell lines. As a result, we identified one particular gene, MEPE/OF45, that is not only higher expressed in A1-5 cells than in B4 cells but also interacts with CHK1 and delays CHK1 ubiquitination. When MEPE/OF45 is knocked down, the cells become more sensitive to IR or CPT-induced death. More importantly, MEPE/OF45 also plays such similar role in human tumor cells. Together, our data indicate a new role of MEPE/OF45, as a regulator of CHK1 ubiquitination, in affecting cells respond to DNA damage.
Key words: MEPE/OF45, CHK1, radiosensitivity, DNA damage response
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