| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 101 === Recent studies indicated that retinoic acid receptor responder 3 (RARRES3/ RIG1/ TIG3) plays an important role in cell proliferation, differentiation, and apoptosis. However, the regulatory mechanism of RARRES3 gene expression has not been clearly elucidated. In this study, we identified a functional p53 response element (p53RE) and estrogen receptor α (ERα) binding site (IR6) in the RARRES3 gene promoter. The expression of RARRES3 mRNA and protein is enhanced through increased p53 protein in HepG2 or in H24-H1299 cells. Transfection studies revealed that the RARRES3 promoter activity was greatly enhanced by wild type but not mutated p53 protein. Sequence specific mutation of the p53RE abolished p53-mediated transactivation and specific binding of p53 protein to rig-p53RE was also demonstrated. The 17β-estradiol-mediated down-regulation of RARRES3 expression was also investigated.The 17β-estradiol-mediated RARRES3 inhibitory effect is directly introduced by the interaction of ERα and IR6 element on the RARRES3 gene promoter. The all trans retinoid acid (atRA) induces RA receptor (RAR) binding in the previously identified response element (DR5) on RARRES3 promoter is also abolished in presence of 17β-estradiol. To further study, the correlation of ERα and p53 was performed in control and p53-knockdown cells. The results demonstrated that 17β-estradiol-suppressed RARRES3 expression was a p53-dependent effect. Results of ChIP assay indicated that the interaction of ERα and RARRES3 promoter was abolished in the 17β-estradiol-treated p53-knockdown cells. It is also influenced the histone modifications and transcriptional cofactors interaction with RARRES3 promoter in p53-knockdown cells. Our results suggest that there is a p53-involved regulatory network modulating 17β-estradiol and atRA mediated RARRES3 gene expression. Wnt/β-catenin signaling pathway is crucial in the regulation of complex biological processes such as cell differentiation and cancer development. Here, we identify a molecular link between RARRES3 and Wnt/β-catenin signaling proteins by the ability of RARRES3 modulates these proteins acylation status. We show that RARRES3 targets and reduces the protein levels of Wnt and the coreceptor low density lipoprotein receptor-related protein 6 (LRP6), resulting in the suppression of cell proliferation, attenuation of Wnt signaling transcriptional activity, reversal of the epithelial-mesenchymal transition (EMT) program, and decrease of cancer stem cells activity. We also found that p53 inactivates cell proliferation and Wnt/β-catenin signaling is related to the ability to activate RARRES3 expression. Thus, our results provide a novel evidence to link p53 and Wnt/β-catenin signaling, in which RARRES3 regulates the signaling-related proteins’ acylation status.
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