The RNA-binding protein nucleolin mediates the pro-proliferative effect of angiotensin II for vascular smooth muscle cells through the post-transcriptional regulation of TGF-β1 and VEGF expression

This study aims to investigate the role of nucleolin in the proliferation of vascular smooth muscle cells (VSMCs) and the underlying molecular mechanism, with a focus on protein-mRNA interactions. Various methods, including BrdU labeling, protein quantification, and CCK-8 cell proliferation assay, were employed to assess the effects of VSMCs proliferation induced by angiotensin II (Ang II) as well as the expressions of TGF-β1 and VEGF at the mRNA and protein levels. Gene transfection, RNA interference, and nucleolin mutant (Nucl-309) were utilized to examine the regulatory impact of nucleolin on the expression and the stability of the TGF-β1 and VEGF mRNA. Additionally, immunoprecipitation, RNA-EMSA, and luciferase reporter gene assays were conducted to investigate the binding of nucleolin to the 3′ UTR of the TGF-β1 and VEGF mRNA. It was found that Ang II increased the DNA synthesis capacity, total cell protein content, and cell survival rate of VSMCs, and the expressions of TGF-β1 and VEGF gradually increased upon stimulation by Ang II. Nucleolin overexpression and knockdown significantly enhanced and inhibited the expressions of TGF-β1 and VEGF, respectively. The overexpression of the nucleolin mutant showed no regulatory effect on the expressions of TGF-β1 and VEGF. The interaction between nucleolin and the 3′ UTR of the TGF-β1 and VEGF mRNA increased their stability and boosted their expressions. Hence, nucleolin plays a key role in promoting Ang II-induced VSMCs proliferation by enhancing the stability of the TGF-β1 and VEGF mRNA through binding to their respective 3′ UTR, which ultimately upregulates their protein expression.