Epigallocatechin‐3‐gallate (EGCG) Inhibits Murine CD4+ T cell Division and Cell Cycle Progression through Modulating Cell Cycle Related‐proteins

Abstract

We have previously reported that EGCG suppresses T cell division through impeding cell cycle. To further determine the molecular mechanism we investigated effect of EGCG on cell cycle-related proteins. Naïve CD4+ T cells from spleen of C57BL/6 mice were stimulated by anti-CD3/CD28 Ab in the presence of 10 µM EGCG. Cell division, cell cycle progression, and cell cycle related-proteins were measured using flow cytometry or Western blot. Stimulation-induced cell division and expression of cell proliferation marker Ki-67 were significantly inhibited by EGCG. Cell cycle analysis showed that stimulation triggered cell cycle progression resulting in reduced proportion of cells in G0/G1 and increased progression into S/G2/M phases. This stimulation-induced process was impeded by EGCG as evidenced by increased cells arrested in G0/G1 phase by 45%, decreased DNA synthesis activity in S phase by 51%, and decreased progression into G2/M phage by 14%. We further showed that EGCG reduced the expression of cell cycle related-proteins Cyclin A, B, and D. Consistent with this, EGCG also inhibited expression of cyclin-dependent kinase (CDK) 2, 4, 5, and 6. In addition, EGCG prevented activation-induced phosphorylation (inactivation) of the cell cycle suppressor retinoblastoma protein and reduction in CDK inhibitor p27Kip1 expression. Together these results suggest that EGCG's inhibitory effect on CD4+T cell division may be due to impeded cell cycle progression, which in turn, is related to altered activity and/or expression of several molecules known to regulate cell cycle progression. Supported by Agriculture and Food Research Initiative Grant 2010-65200-20360, and USDA contract #58-1950-0-014.