Epigallocatechin Gallate Inhibits Phorbol Ester-Induced Activation of NF-κB and CREB in Mouse Skin Role of p38 MAPK

摘要

The modulation of intracellular signaling network involved in an inappropriate expression of cyclooxygenase-2 (COX-2) is a prag matic approach for chemoprevention with a wide variety of dietary phytochemicals. Epigallocatechin gallate (EGCG), a major green tea polyphenol, is one of the most extensively investigated chemopreventive agents. Our previous study revealed that EGCG inhibited expression of COX-2 and activation of mitogen-activated protein kinases (MAPKs) in mouse skin stimulated with a prototype tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA). This study was aimed at identi fying transcription factors as molecular targets of EGCG in downregu lating COX-2 expression. We found that EGCG inhibited TPA-induced DNA binding of NF-κB and CREB in mouse skin in vivo. EGCG also suppressed TPA-induced phosphorylation and subsequent degradation of IκBα, and prevented nuclear translocation of p65. We also exam ined whether extracellular signal-regulated protein kinase (ERK) and p38 MAPK, which are known to regulate activation of NF-κB, can also modulate CREB DNA binding. Pretreatment with U0126 and SB203580, pharmacological inhibitors of ERK and p38 MAPK, respectively, showed that SB203580, but not U0126, attenuated TPA-induced CREB DNA binding in mouse skin. Taken together, EGCG inhibited TPA-induced DNA binding of NF-κB and CREB by blocking activation of p38 MAPK, which may provide a molecular basis of COX-2 inhibition by EGCG in mouse skin in vivo.