HTLV-1 Tax Functions as a Ubiquitin E3 Ligase for Direct IKK Activation via Synthesis of Mixed-Linkage Polyubiquitin Chains

PLoS Pathog. 2016 Apr 15;12(4):e1005584. doi: 10.1371/journal.ppat.1005584. eCollection 2016 Apr.

Abstract

The HTLV-1 oncoprotein Tax plays a key role in CD4+ T cell transformation by promoting cell proliferation and survival, mainly through permanent activation of the NK-κB pathway and induction of many NF-κB target genes. Elucidating the underlying molecular mechanism is therefore critical in understanding HTLV-1-mediated transformation. Current studies have suggested multiple but controversial mechanisms regarding Tax-induced IKK activation mainly due to blending of primary Tax-induced IKK activation events and secondary IKK activation events induced by cytokines secreted by the primary Tax-induced IKK-NF-κB activation events. We reconstituted Tax-stimulated IKK activation in a cell-free system to dissect the essential cellular components for primary IKK activation by Tax and studied the underlying biochemical mechanism. We found that Tax is a putative E3 ubiquitin ligase, which, together with UbcH2, UhcH5c, or UbcH7, catalyzes the assembly of free mixed-linkage polyubiquitin chains. These free mixed-linkage polyubiquitin chains are then responsible for direct IKK activation by binding to the NEMO subunit of IKK. Our studies revealed the biochemical function of Tax in the process of IKK activation, which utilizes the minimal cellular ubiquitination components for NF-κB activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatography, High Pressure Liquid
  • Enzyme Activation / physiology*
  • Gene Knockout Techniques
  • Gene Products, tax / metabolism*
  • HEK293 Cells
  • HTLV-I Infections / metabolism*
  • Humans
  • I-kappa B Kinase / metabolism*
  • Immunoblotting
  • Jurkat Cells
  • NF-kappa B / metabolism
  • Polyubiquitin / biosynthesis*
  • Signal Transduction / physiology
  • Tandem Mass Spectrometry
  • Transfection
  • Ubiquitin-Protein Ligases / metabolism*

Substances

  • Gene Products, tax
  • NF-kappa B
  • tax protein, Human T-lymphotrophic virus 1
  • Polyubiquitin
  • Ubiquitin-Protein Ligases
  • I-kappa B Kinase

Grants and funding

This study was supported by the National Basic Research Program of China (973 Program, http://www.most.gov.cn/eng/programmes1/200610/t20061009_36223.htm, 2013CB945000 to ZX), the Natural Science Foundation of China (http://www.nsfc.gov.cn/, 31371416 and 31571445 to ZX), the Program for New Century Excellent Talents in University of China (NCET-11-0458 to ZX) and by the Fundamental Research Funds for the Central Universities. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.