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

// Jianglin Zhang 1, 2, * , Zhou Lei 1, 2, * , Zunnan Huang 3, * , Xu Zhang 1, 2 , Youyou Zhou 1, 2 , Zhongling Luo 1, 2 , Weiqi Zeng 1, 2 , Juan Su 1, 2 , Cong Peng 1, 2 , Xiang Chen 1, 2 1 The Department of Dermatology, Xiangya Hospital, Central South University, Changsha, Hunan, China 2 Hunan Key Laboratory of Skin Cancer and Psoriasis, Xiangya Hospital, Central South University, Changsha, Hunan, China 3 Key Laboratory for Medical Molecular Diagnostics of Guangdong Province, Dongguan Scientific Research Center, Guangdong Medical University, Dongguan, Guangdong, China * These authors have contributed equally to this work Correspondence to: Cong Peng, email: pengcongxy@csu.edu.cn Xiang Chen, email: chenxiangck@126.com Keywords: EGCG, TRAF6, ubiquitination, melanoma Received: August 24, 2016 Accepted: October 07, 2016 Published: October 24, 2016 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.