The expression of RNA helicase DDX5 is transcriptionally upregulated by calcitriol through a vitamin D response element in the proximal promoter in SiHa cervical cells.

ABSTRACT

The DEAD box RNA helicase DDX5 is a multifunctional protein involved in the regulatory events of gene expression. Herein, we presented evidence indicating that DDX5 is transcriptionally upregulated by calcitriol, the hormonal form of vitamin D3. In silico analysis revealed the presence of two putative vitamin D response elements (VDREs) in the DDX5 promoter region. Using luciferase reporter assays, we demonstrated that the DDX5 promoter containing these putative VDREs significantly increased the luciferase activity in vitamin D receptor (VDR)-positive SiHa cells upon calcitriol treatment. Electrophoretic mobility shift assays showed the ability of VDR and retinoid X receptor to interact only with the most proximal VDRE, while chromatin immunoprecipitation analysis confirmed the occupancy of this VDRE by the VDR. Finally, we demonstrated that calcitriol significantly increased both DDX5 mRNA and protein in SiHa cells. In summary, this study shows that DDX5 gene is transcriptionally upregulated by calcitriol through a VDRE located in its proximal promoter. Given the importance of DDX5 as a master regulator of differentiation programs, our study suggests that the pro-differentiating properties of calcitriol may be related with the induction of DDX5.