Epigallocatechin-3-gallate(EGCG) suppresses melanoma cell growth and metastasis by targeting TRAF6 activity

Abstract

TRAF6 (TNF Receptor-Associated Factor 6) is an E3 ubiquitin ligase that contains a Ring domain, induces K63-linked polyubiquitination, and plays a critical role in signaling transduction. Our previous results demonstrated that TRAF6 is overexpressed in melanoma and that TRAF6 knockdown dramatically attenuates tumor cell growth and metastasis. In this study, we found that EGCG can directly bind to TRAF6, and a computational model of the interaction between EGCG and TRAF6 revealed that EGCG probably interacts with TRAF6 at the residues of Gln54, Gly55, Asp57 ILe72, Cys73 and Lys96. Among these amino acids, mutation of Gln54, Asp57, ILe72 in TRAF6 could destroy EGCG bound to TRAF6, furthermore, our results demonstrated that EGCG significantly attenuates interaction between TRAF6 and UBC13(E2) and suppresses TRAF6 E3 ubiquitin ligase activity in vivo and in vitro. Additionally, the phosphorylation of IκBα, p-TAK1 expression are decreased and the nuclear translocation of p65 and p50 is blocked by treatment with EGCG, leading to inactivation of the NF-κB pathway. Moreover, EGCG significantly inhibits cell growth as well as the migration and invasion of melanoma cells. Taken together, these findings show that EGCG is a novel E3 ubiquitin ligase inhibitor that could be used to target TRAF6 for chemotherapy or the prevention of melanoma.

Naturally occurring anti-cancer compounds: shining from Chinese herbal medicine

“…In contrast, it induces cell death via apoptosis and autophagy in oral squamous cell carcinoma SCC-4 cells [84], so autophagy plays a dual role in EGCG-induced cell death. It can also suppress metastasis in human melanoma SK-MEL-5, SK-MEL-28, A375 and G361, NSCLC CL1-5, A549 and H1299 cells, and lung metastasis mice [85,93,100]. In addition, EGCG suppresses tumor angiogenesis in human NSCLC A549 cells and A549 xenograft mice [101].…”

“…EGCG possesses various biological effects including anti-obesity and anti-hyperuricemia, anti-oxidative, anti-viral, anti-bacterial, anti-infective, anti-angiogenic, anti-inflammatory and anti-cancer activities [80][81][82][83][84]. It is reported to present anti-cancer effects in variety of cancer cells, including lung, colorectal, prostate, stomach, liver, cervical, breast, leukemia, gastric, bladder cancers [85][86][87][88][89][90]. Among its anti-cancer activities, EGCG exhibits multiple pharmacological actions, including the suppression of cell growth, proliferation, metastasis and angiogenesis, induction of apoptosis, and enhancement of anti-cancer immunity [85,86,[91][92][93][94].…”

“…Similarly, EGCG causes 78-kDa glucose-regulated protein (GRP78) accumulation in the ER, which up-regulates ER stress markers such as activating transcription factor 4 (ATF-4), X-box binding protein 1 (XBP-1) and C/EBP homologous protein (CHOP), and shifts into pro-apoptotic ER stress, leading to increased caspase-3 and -8 activities [107]. Furthermore, it suppresses cell migration and invasion by blocking tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), MMP-2/c-Jun N-terminal kinase (JNK) and transforming growth factor-β (TGF-β) pathways [85,93,100].…”

Epigallocatechin-3-Gallate Ameliorates Angiotensin II-Induced Oxidative Stress and Apoptosis in Human Umbilical Vein Endothelial Cells through the Activation of Nrf2/Caspase-3 Signaling

“…(−)-Epigallocatechin-3-gallate (EGCG), the major compound of green tea, has anti-inflammatory, antioxidative, and antiangiogenic effects both in vitro and in vivo [17,18,19]. EGCG enhances cancer cell apoptosis [20,21].…”

A Novel Chalcone derivative suppresses Melanoma cell growth through targeting Fyn/Stat3 pathway

“…Lj-1-60-linked sepharose 4B beads pretreated as described previously [18]. Proteins (approximately 500 μg) coupled with Lj-1-60-linked sepharose 4B beads reacted in incubation buffer, and sepharose 4B alone as control.…”