Epigallocatechin-3-gallate causes the p21/WAF1-mediated G1-phase arrest of cell cycle and inhibits matrix metalloproteinase-9 expression in TNF-α-induced vascular smooth muscle cells

It has been suggested that epigallocatechin-3-gallate (EGCG), a major catechin found in green tea, plays a role in preventing the progression of atherosclerosis. Although EGCG has anti-atherogenic effects on vascular smooth muscle cells (VSMC), the molecular mechanisms associated with TNF-α-induced VSMC are not known with certainty. To determine whether EGCG has the capacity to modulate VSMC responses, cell cycle regulation and MMP-9 expression were examined in TNF-α-induced VSMC. Treatment with EGCG, which blocks the cell cycle in the G1 phase, induced a down-regulation of cyclins and CDKs and an up-regulation in the expression of p21/WAF1, a CDK inhibitor, whereas the up-regulation of p27 by EGCG was not observed. Moreover, treatment with EGCG markedly increased the promoter activity of the p21/WAF1 gene. Immunoblot and deletion analysis results for the p21/WAF1 promoter showed that EGCG induced the expression of p21/WAF1 independent of the p53 pathway. Zymographic and immunoblot analyses showed that EGCG suppressed TNF-α-induced MMP-9 expression in a dose-dependent manner. Further experiments demonstrated that EGCG reduced the transcriptional activity of activator protein-1 (AP-1) and nuclear factor kappaB (NF-κB), two important nuclear transcription factors that are involved in MMP-9 expression. Collectively, these results suggest that EGCG inhibits G1 to S-phase cell cycle progress and MMP-9 expression through the transcription factors NF-κB and AP-1 in TNF-α-induced VSMC.