Modulation of gene expression by (-)-epigallocatechin gallate in PC-9 cells using a cDNA expression array

Green tea is the most effective cancer preventive beverage. In the light of this, the mechanisms of action of tea polyphenols were investigated on the molecular levels. We present here the effects of (-)-epigallocatechin gall ate (EGCG) on expression of 588 genes in human lung cancer cell line PC-9 c ells, using a human cancer cDNA expression array. The levels of gene expres sion in non-treated control cells, and cells treated with EGCG alone, with the tumor promoter okadaic acid alone, and with EGCG plus okadaic acid, wer e studied, and their expression levels were classified into down-regulation (under 0.5 fold) and up-regulation (over 2.0 fold) by comparing with the l evels of control. Non-treated PC-9 cells expressed 163 genes out of 588, an d EGCG-treated cells induced down-regulated expression of 12 genes and up-r egulated expression of 4 other genes. From a comparison of gene expression in the cells treated with EGCG and in cells treated with EGCG plus okadaic acid, we found the following genes commonly affected by EGCG: down-regulati on of four genes, NF-kappaB inducing kinase (NIK), death-associated protein kinase I (DAPK 1), rhoB and tyrosine-protein kinase (SKY); up-regulation o f one gene, retinoic acid receptor al. Among them, we think down-regulation of NIK gene expression is significant for cancer prevention, based on evid ence that inhibition of NF-kappaB activation is a result of inhibition of N IK/IKK signalling complex.