Promoter activation and following induction of the p21/WAF1 gene by flavone is involved in G1 phase arrest in A549 lung adenocarcinoma cells.

Flavonoids are present in many plants including edible fruits and vegetables. Recently, many of the biological activities of flavonoids have been elucidated. Flavone is a well known flavonoid, and many of its derivatives have been shown to have anti-proliferative effects on several cancer cells. We report here that flavone can effectively inhibit the cell growth of human lung adenocarcinoma A549 cells in a dose-dependent manner, and 100 microM flavone causes cell cycle arrest at the G1 phase. As a mechanism underlying the cell cycle arrest, flavone markedly increases the mRNA and protein levels of a universal inhibitor of cyclin-dependent kinase, p21/WAF1, and inhibits phosphorylation of retinoblastoma (RB) protein. Although A549 cells possess wild-type p53, flavone does not induce the p53 protein, suggesting that p21/WAF1 induction is p53-independent. In addition, 100 microM flavone significantly increases the promoter activity of the p21/WAF1 gene by 5-fold. These results suggest that the G1 phase arrest by flavone is due to p53-independent transcriptional induction of the p21/WAF1 gene and the subsequent dephosphorylation of RB protein.