EGCG Inhibits the Invasion of Highly Invasive CL1-5 Lung Cancer Cells through Suppressing MMP-2 Expression via JNK Signaling and Induces G2/M Arrest

Tumor metastasis is the main obstacle to the treatment of lung cancer. According to previous findings, matrix metalloproteinase-2 (MMP-2) is closely correlated with metastatic potential in lung cancer. This study showed that epigallocatechin-3-gallate (EGCG), a natural polyphenol in green tea, is a potent inhibitor of MMP-2 expression. EGCG effectively suppressed the invasion and migration of highly invasive CL1-5 lung cancer cells. Gelatin zymography, Western blot analysis, and RTPCR were used to investigate the effects of EGCG on MMP-2 expression. The effects of EGCG on cell cycle and apoptosis were determined by flow cytometry analysis. To investigate the effects of EGCG on cell migration and cell invasion, Transwell migration/invasion assays were used. EGCG downregulated MMP-2 expression at the transcriptional level in CL1-5 cells. Moreover, the treatment of CL1-5 cells with EGCG caused downregulation of c- Jun N-terminal kinase (JNK), resulting in repression of the translocation of transcriptional factors, Sp1, and NF-kappa B, from the cytosol into the nucleus. In addition, EGCG significantly and synergistically enhanced the antitumor effects of the clinical drug, docetaxel, in CL1-5 cells. Further, EGCG induced G2/M arrest at dosages higher than those of suppression in cell invasion in CL1-5 cells. These results reveal that EGCG might decrease MMP-2 mRNA expression through JNK signaling, further suggesting that a combination of EGCG and docetaxel may be a promising strategy to help increase the efficacy of docetaxel in suppressing metastasis in lung cancer cells. In addition, EGCG may suppress cell proliferation in CL1-5 cells through inducing G2/M arrest.