Background: Reactive oxygen species, such as superoxide (O(2)(-)), are involved in the abnormal growth of various cell types. Angiotensin II (Ang II) is one of the most potent inducers of oxidative stress in the vasculature. The molecular events involved in Ang II-induced proliferation of vascular smooth muscle cells (VSMCs) are only partially understood.
Methods and results: Ang II as well as xanthine/xanthine oxidase (X/XO) led to enhanced DNA synthesis and proliferation of VSMCs. The effect of Ang II was abolished by diphenylene iodonium. Consequently, VSMCs were incubated with X/XO, and modulation of gene expression was monitored by differential display, leading to the identification of a novel redox-sensitive gene, the dominant-negative helix-loop-helix protein Id3, which was upregulated within 30 minutes by X/XO and Ang II. Superoxide dismutase but not catalase inhibited this effect. Overexpression of antisense Id3 via transfection in VSMCs completely abolished Ang II- and X/XO-induced cell proliferation. Ang II, X/XO, and overexpression of sense Id3 downregulated protein expression of p21(WAF1/Cip1), p27(Kip1), and p53. Overexpression of antisense Id3 abrogated the effect of Ang II on the expression of p21(WAF1/Cip1), p27(Kip1), and p53. Ang II and overexpression of sense Id3 caused hyperphosphorylation of the retinoblastoma protein. Ang II-induced phosphorylation of the retinoblastoma protein was decreased by overexpression of antisense Id3.
Conclusions: Ang II induces proliferation of VSMCs via production of superoxide, which enhances the expression of Id3. Id3 governs the downstream mitogenic processing via depression of p21(WAF1/Cip1), p27(Kip1), and p53. These findings reveal a novel redox-sensitive pathway involved in growth control.