title: Epstein-Barr virus BGLF4 kinase downregulates NF-κB transactivation through phosphorylation of coactivator UXT.
abstract: Epstein-Barr virus (EBV) BGLF4 is a member of the conserved herpesvirus kinases that regulate multiple cellular and viral substrates and play an important role in the viral lytic cycles. BGLF4 has been found to phosphorylate several cellular and viral transcription factors, modulate their activities, and regulate downstream events. In this study, we identify an NF-κB coactivator, UXT, as a substrate of BGLF4. BGLF4 downregulates not only NF-κB transactivation in reporter assays in response to tumor necrosis factor alpha (TNF-α) and poly(I·C) stimulation, but also NF-κB-regulated cellular gene expression. Furthermore, BGLF4 attenuates NF-κB-mediated repression of the EBV lytic transactivators, Zta and Rta. In EBV-positive NA cells, knockdown of BGLF4 during lytic progression elevates NF-κB activity and downregulates the activity of the EBV oriLyt BHLF1 promoter, which is the first promoter activated upon lytic switch. We show that BGLF4 phosphorylates UXT at the Thr3 residue. This modification interferes with the interaction between UXT and NF-κB. The data also indicate that BGLF4 reduces the interaction between UXT and NF-κB and attenuates NF-κB enhanceosome activity. Upon infection with short hairpin RNA (shRNA) lentivirus to knock down UXT, a spontaneous lytic cycle was observed in NA cells, suggesting UXT is required for maintenance of EBV latency. Overexpression of wild-type, but not phosphorylation-deficient, UXT enhances the expression of lytic proteins both in control and UXT knockdown cells. Taking the data together, transcription involving UXT may also be important for EBV lytic protein expression, whereas BGLF4-mediated phosphorylation of UXT at Thr3 plays a critical role in promoting the lytic cycle.
authors.affiliation: Graduate Institute and Department of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Ling-Shih
authors.initials: LS
authors.lastname: Chang
authors.forename: Jiin-Tarng
authors.initials: JT
authors.lastname: Wang
authors.forename: Shin-Lian
authors.initials: SL
authors.lastname: Doong
authors.forename: Chung-Pei
authors.initials: CP
authors.lastname: Lee
authors.forename: Chou-Wei
authors.initials: CW
authors.lastname: Chang
authors.forename: Ching-Hwa
authors.initials: CH
authors.lastname: Tsai
authors.forename: Sheng-Wen
authors.initials: SW
authors.lastname: Yeh
authors.forename: Ching-Yueh
authors.initials: CY
authors.lastname: Hsieh
authors.forename: Mei-Ru
authors.initials: MR
authors.lastname: Chen
mesh_terms: D018797:Cell Cycle Proteins; D015536:Down-Regulation; D015967:Gene Expression Regulation, Viral; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D018832:Molecular Chaperones; D016328:NF-kappa B / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D018832:Molecular Chaperones; D016328:NF-kappa B; D009363:Neoplasm Proteins; D014409:Tumor Necrosis Factor-alpha; C118920:UXT protein, human; D014764:Viral Proteins; C406063:BGLF4 protein, Epstein-Barr virus; D017346:Protein Serine-Threonine Kinases