HTLV-1 Tax Stimulates Ubiquitin E3 Ligase, Ring Finger Protein 8, to Assemble Lysine 63-Linked Polyubiquitin Chains for TAK1 and IKK Activation

• DOI: 10.1371/journal.ppat.1005102
• Publication Date: 2015-08-18T18:02:09Z
• Authors: Yik-Khuan Ho; Huijun Zhi; Tara Bowlin; Batsukh Dorjbal; Subha Philip; Muhammad Atif Zahoor; Hsiu-Ming Shih; Oliver John Semmes; Brian Schaefer; J. N. Mark Glover; Chou-Zen Giam
• Keywords: IκB kinase; Jurkat cells; Ubiquitin-conjugating enzyme

Human T lymphotropic virus type 1 (HTLV-1) trans-activator/oncoprotein, Tax, impacts a multitude of cellular processes, including I-κB kinase (IKK)/NF-κB signaling, DNA damage repair, and mitosis. These activities Tax have been implicated in the development adult T-cell leukemia (ATL) HTLV-1-infected individuals, but underlying mechanisms remain obscure. IKK its upstream kinase, TGFβ-activated (TAK1), contain ubiquitin-binding subunits, NEMO TAB2/3 respectively, which interact with K63-linked polyubiquitin (K63-pUb) chains. Recruitment to K63-pUb allows cross auto-phosphorylation activation TAK1 occur, followed by TAK1-catalyzed phosphorylation activation. Using cytosolic extracts HeLa Jurkat cells supplemented purified proteins we identified ubiquitin E3 ligase, ring finger protein 8 (RNF8), E2 conjugating enzymes, Ubc13:Uev1A Ubc13:Uev2, be factors utilized for In vitro, combination RNF8 greatly stimulated TAK1, IKK, IκBα JNK phosphorylation. vivo, over-expression augmented while ablation drastically reduced canonical NF-κB Tax. Activation non-canonical pathway however, is unaffected loss RNF8. components, further demonstrated biochemically that Ubc13:Uev1A/Uev2 assemble long Finally, co-transfection increasing amounts induced assembly dose-dependent manner. Thus, targets promote chains, signal multiple downstream kinases JNK. Because roles chains play repair cytokinesis, this mechanism may also explain genomic instability HTLV-1-transformed ATL cells.