Regulation of p21 expression for anti-apoptotic activity of DDX3 against sanguinarine-induced cell death on intrinsic pathway

Background: DDX3 plays a role in multicellular pathways, especially exerting an anti-apoptotic effect on extrinsic apoptosis. However, studies on the role of DDX3 in intrinsic apoptosis are lacking. Purpose: In this study, we aimed to study the bio-function of DDX3 anti-apoptotic activity in the intrinsic pathway using HeLa cells treated with sanguinarine. Study design: Screening of apoptosis-inducing agents found that sanguinarine was the most effective. After treatment with sanguinarine, cell viability, caspase-3 activity, and intrinsic gene expression were analyzed. FACS assays were used to analyze the effect of overexpression and knockdown of DDX3 to determine its role on intrinsic apoptosis. The relationship between DDX3 and the inhibition of p21 and apoptosis was investigated. Results: Sanguinarine was determined to be the most effective intrinsic apoptosis-inducing agent in HeLa cervical cancer cells. DDX3 upregulated anti-apoptotic gene expression (Bcl-xL, cyclin D1, cyclin E, and cyclin B1) and downregulated pro-apoptotic gene expression (caspase-3, Bax) after sanguinarine treatment. The apoptotic cell death rate increased from 8.74% (sanguinarine-treated control) to 17.6% after the knockdown of DDX3 but decreased to 5.29% after DDX3 overexpression. The results implied that p21 might be involved in the toxicity of sanguinarine to HeLa cells. Overexpression and knockdown of DDX3 under sanguinarine-treated conditions showed that DDX3 inhibited p21 expression in sanguinarine-treated HeLa cells. Notably, when we tested p21 expression among eight mutants located in the functional residues of DDX3 (590A, S90E, T204A, T204E, GET, NEAD, LAT, and HRISR) under sanguinarine-treated conditions, only the 590E mutation in DDX3 had an effect on the inhibition of p21 expression and levels of pro-apoptotic genes (Bax and caspase-3) and anti-apoptotic genes (Bcl-xL, cyclin D1, cyclin E, and cyclin B1), as well as DDX3. Conclusion: Taken together, the results suggest that the 590E residue is important for the regulation of p21 expression responsible for the anti-apoptotic activity of DDX3 in HeLa cells treated with sanguinarine. A model of the antiapoptotic function of DDX3 on sanguinarine-treated HeLa cells was proposed to understand the molecular mechanism of the intrinsic apoptosis inhibition in cervical cancer cells.