EGCG, An Effective Antagonist Of STAT3Signaling Pathway

Hepatocelluler carcinoma (HCC) is one of the most common types of human cancers.Patients with HCC have very low survival rates. Signal Transducer and Activator ofTranscription type3(STAT3) is an oncogene that promotes cell survival, proliferation,motility and progression in Hepatocelluler cancer cells. In this study, we explored thepharmacological potential of a STAT3inhibitor: epigallocatechin-3-gallate(EGCG), a widely investigated tumor-preventive agent. It has been reportedthat EGCG can inhibit activation of several types of molecular factors, contributing tothe inhibition of multiple downstream signaling pathways such as STAT3/JAKpathway.When applied to BEL-7402and QGY-7701cells in-vitro, we used MTT method toprove that proliferation and migration of these two cell lines were strongly suppressedby EGCG. EGCG led to a significant dose-depentent inhibition of HCC cell growth invitro.The concentration to achieve50%growth inhibition (IC50) for BEL-7402andQGY-7704cells was about55μM and35μM,respectively.We demonstrated thatEGCG induces apoptosis by interfering with the STAT3signaling pathway using flowcytometer method. The apoptosis rates of BEL-7402cells treated with20μM,40μM,80μM and160μM of EGCG are4.4%,6.7%,8.5%and35.6%, respectively. Similarly,The apoptosis rates of QGY-7704cells treated with20μM,40μM,80μM and160μMof EGCG for24hours are9.1%,15.3%,22.7%and50.6%, respectively(P<0.05).These results demonstate that QGY-7704cell line is more sensitive to the interferenceof EGCG than BEL-7402cell line. Meanwhile, the level of STAT3phosphorylationdecreased dramatically, while the level of total signal transduction and activators oftranscription(T-STAT3) showed less of a change. RT-PCR results showed that EGCGinhibited the expression of STAT3-regulated genes, resulting in the inhibition of HCCcell proliferation, migration and invasion.Moreover, we used the molecule DOCKING to explore the interaction betweenSTAT3and EGCG. The–C=O group as H receptor in EGCG formed hydrogen bonding with-NH in GLU612and-OH in SER613. These are also strong interaction.In addition, one aromatic as the H donor in EGCG formed hydrogen bondinginteraction with the–NH2group in ARG609. The other part of EGCG formed Vanderwaals interaction with the hydrophobic pocket of STAT3SH2(LYS591, GLU594,ARG609, SER611, GLU612, SER613, THR620, VAL637, GLU638, PRO639. Theresults were consistent with the PT-PCR findings, confirming that EGCG suppressesSTAT3on a molecular level. All in all, these results demonstrated that EGCG cansuppress the growth, invasion and migration of HCC cells, and induce apoptosis byinterfering with the STAT3signaling pathway.