Tax ubiquitylation and SUMOylation control the dynamic shuttling of Tax and NEMO between Ubc9 nuclear bodies and the centrosome

Abstract

The human T-lymphotropic virus type I oncoprotein Tax is critical for T-cell transformation, acting mainly through nuclear factor kappa B essential modulator (NEMO) binding and subsequent nuclear factor-B activation. Tax localizes to Tax nuclear bodies and to the centrosome and is subjected to ubiquitylation and small ubiquitin-like modifier (SUMO)ylation, which are both necessary for complete transcriptional activation. Using the photoconvertible fluorophore Dendra-2 coupled with live video confocal microscopy, we show for the first time that the same Tax molecule shuttles among Tax nuclear bodies and between these nuclear bodies and the centrosome, depending on its posttranslational modifications. Ubiquitylation targets Tax to nuclear bodies to which NEMO is recruited and subsequently SUMOylated. We also demonstrate that Tax nuclear bodies contain the SUMOylation machinery including SUMO and the SUMO conjugating enzyme Ubc9, strongly suggesting that these nuclear bodies represent sites of active SUMOylation. IntroductionTax, the viral oncoprotein encoded by the pX region of the human T-lymphotropic virus type I (HTLV-I) genome is a key player in the pathogenesis of HTLV-I-associated diseases, mainly adult T-cell leukemia/lymphoma and tropical spastic paraparesis/HTLVassociated myelopathy. Tax deregulates the cellular machinery at multiple levels leading to the transformation of HTLV-I-infected T lymphocytes, predominantly through the activation of the nuclear factor-B (NF-B) pathway, which regulates key genes implicated in inflammation, apoptosis, and oncogenesis. 1,2 A corner stone in this NF-B activation is Tax binding to the regulatory subunit of the IB kinase (IKK) complex, IKK␥ (also known as NEMO). 3,4 Tax binding to NEMO phosphorylates both IKK␣ and IKK␤ leading to the formation of the IKK complex that phosphorylates the NF-B inhibitors IBs. This leads to the nuclear translocation of the active NF-B dimers and to transcriptional activation of target genes. 5 Tax/NEMO binding can also induce the IKK␣-dependent processing of the NF-B p100 precursor protein to its active p52 form. 6 Tax displays a dual nuclear and cytoplasmic localization with functions that are essential for cellular transformation in each compartment. 7,8 In the nucleus, Tax is predominantly located in RelA-enriched nuclear bodies. 9 In the cytoplasm, a major fraction of Tax lays in perinuclear hotspots colocalizing with the centrosome or microtubule organizing center in close association with the cis-Golgi compartment. 10,11 Posttranslational modification of proteins regulates protein functions by modifying their subcellular localization, stability, and/or network of interaction. We and others have described different forms of Tax posttranslational modifications including phosphorylation, 12,13 acetylation, 14 ubiquitylation, and small ubiquitin-like modifier (SUMO)ylation, 15,16 all of which are implicated in Tax-mediated activation of gene expression. Indeed, we showed that Tax is differentially ubiquitylated by either K-48 ubiquitin...

An RNA Interference Screen Identifies the Deubiquitinase STAMBPL1 as a Critical Regulator of Human T-Cell Leukemia Virus Type 1 Tax Nuclear Export and NF-κB Activation

“…Polyubiquitination of Tax plays a critical role in IKK␥ binding, Tax trafficking, and NF-B activation (20,27). However, the regulation of Tax polyubiquitination and NF-B activation by host proteins is poorly understood.…”

“…Tax undergoes a number of posttranslational modifications, including ubiquitination and sumoylation, that regulate Tax trafficking in cells (27). Whereas ubiquitinated Tax is predominantly found in the cytoplasm, sumoylated Tax is located primarily in the nucleus.…”

“…Recent studies have shown that posttranslational modifications of Tax regulate its function by governing its subcellular localization, stability, and protein-protein interactions (6,20,32). Tax is modified by a number of distinct posttranslational modifications, including ubiquitination, small ubiquitin (Ub)-like modifier sumoylation, phosphorylation, and acetylation (3,6,11,26,27,41), all of which regulate Tax function. In particular, ubiquitination and sumoylation of Tax play important roles in Tax trafficking and NF-B activation.…”

Ubiquitin-Specific Peptidase 20 Targets TRAF6 and Human T Cell Leukemia Virus Type 1 Tax To Negatively Regulate NF-κB Signaling

“…Ubiquitination, sumoylation, acetylation, and phosphorylation of Tax have been shown to influence its transcriptional function (5,9,22,23,25,28,34,35,40). Tax ubiquitination has been reported to be required for its activation of NF-B, and it has been found that the Tax-polyubiquitin chains are predominantly K63 linked (40).…”

The Role of HTLV-1 in Alteration of Immune Regulation Through Regulatory T Cell Dysfunction and Exosomal Manipulation

“…Cytoplasmic retention is essential for IKK and NF-kB activation, and may be important for exosome localization as detailed earlier . HTLV-1 Tax also undergoes sumolyation, which aids in nuclear retention and the formation of nuclear bodies that consist of Tax and binding partners CBP and p300 (Kfoury et al, 2011). The sites for sumoylation on the protein overlap with the sites of ubiquitination.…”