The current study aimed to clarify the role of nucleolin in the phenotypic transformation of vascular smooth muscle cells (VSMcs) and to preliminarily explore its underlying mechanism. The spatial and temporal expression patterns of nucleolin, and the effects of angiotensin II (Ang II) on the expression of VSMc phenotypic transformation markers, α-smooth muscle-actin, calponin, smooth muscle protein 22α and osteopontin were investigated. The effects of nucleolin on VSMc phenotypic transformation and the expression of phenotypic transformation-associated genes, tropoelastin, epiregulin and fibroblast growth factor 2 (b-FGF), were determined. Protein-RNA co-immunoprecipitation was used to investigate the potential target genes regulated by the nucleolin in phenotypic transformation of VSMcs. Finally, the stability of tropoelastin mRNA and the effects of nucleolin on the expression of tropoelastin were assayed. The results revealed that Ang II significantly promoted the phenotypic transformation of VSMcs. The expression of nucleolin was gradually upregulated in VSMcs treated with Ang II at different concentrations for various durations. Ang II induced nucleolin translocation from the nucleus to cytoplasm. Additionally, Ang II significantly promoted the phenotypic transformation of VSMcs. Overexpression and silencing of nucleolin regulated the expressions of tropoelastin, epiregulin and b-FGF. There was an interaction between tropoelastin mRNA and nucleolin protein, promoting the stability of tropoelastin mRNA and enhancing the expression of tropoelastin at the protein level. Upregulation of nucleolin had an important role in Ang II-induced VSMc phenotypic transformation, and its underlying mechanism may be through interacting with tropoelastin mRNA, leading to its increased stability and protein expression. The findings provide a new perspective into the regulatory mechanism of VSMc phenotypic transformation.

RNA‐binding properties of nucleolin play a fundamental role in regulating cell growth and proliferation. We have previously shown that nucleolin plays an important regulatory role in the phenotypic transformation of vascular smooth muscle cells (VSMCs) induced by angiotensin II (Ang II). In the present study, we aimed to investigate the molecular mechanism of nucleolin‐mediated phenotypic transformation of VSMCs induced by Ang II. Epidermal growth factor (EGF) and platelet‐derived growth factor (PDGF) inhibitors were used to observe the effect of Ang II on phenotypic transformation of VSMCs. The regulatory role of nucleolin in the phenotypic transformation of VSMCs was identified by nucleolin gene mutation, gene overexpression and RNA interference technology. Moreover, we elucidated the molecular mechanism underlying the regulatory effect of nucleolin on phenotypic transformation of VSMCs. EGF and PDGF‐BB played an important role in the phenotypic transformation of VSMCs induced by Ang II. Nucleolin exerted a positive regulatory effect on the expression and secretion of EGF and PDGF‐BB. In addition, nucleolin could bind to the 5′ untranslated region (UTR) of EGF and PDGF‐BB mRNA, and such binding up‐regulated the stability and expression of EGF and PDGF‐BB mRNA, promoting Ang II‐induced phenotypic transformation of VSMCs.