Ubiquitin-Specific Protease 4 (USP4) Targets TRAF 2/6 For Deubiquitination And Inhibits TNFα-induced Cell Migration

Ubiquitination of intermediates in the NF-κB signaling pathway plays an important role in activation and regulation of the pathway. The adapter protein tumor necrosis factor associated factor-6 or 2 (TRAF6 or TRAF2) is such a signaling intermediate that is crucial for mediating signal transduction from members of the IL-1R/TLR and TNFR superfamilies. Both of them are E3 ubiquitin ligases that can mediate the K63-linked ubiquitination of their substrates and themselves. Moreover, the self-ubiquitination is very important for their self-activation and activating downstream of the signaling pathway. Recently, more and more studies have revealed that deuibiquitination mediated by DUBs is comparable with ubiquitination involving in regulating NF-κB signaling pathway, among which CYLD and A20 are the best characterized. CYLD inhibits IKK activation by cleaving K63-linked polyubiquitin chains on several proteins including TRAF2, TRAF6 and NEMO, and A20 negatively regulates NF-κB signaling by reducing ubiquitination of TRAF2, TRAF6, and RIP1. However, whether there are other DUBs and which of the targeted NF-κB signaling molecules were involved in regulating NF-κB signaling pathway remain to be further studied.Here, by using the approach of screening we identified USP4 as a new deuibiquitinase targeting TRAF6/TRAF2 for deubiquitination and inhibiting the activation of NF-κB. In addition to that, we found TNFa can cause the increasing motility of lung cancer cells A549 and knockdown USP4 can promote the cell migration of A549 cells induced by TNF-α. All of these suggested the role and function of USP4 in regulating NF-κB signaling and cell migration.