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A novel positive feedback-loop between the HTLV-1 oncoprotein Tax and NF-?B activity in T-cells.

ABSTRACT: BACKGROUND:Human T-cell leukemia virus type 1 (HTLV-1) infects primarily CD4+ T-lymphocytes and evoques severe diseases, predominantly Adult T-Cell Leukemia/ Lymphoma (ATL/L) and HTLV-1-associated Myelopathy/ Tropical Spastic Paraparesis (HAM/TSP). The viral transactivator of the pX region (Tax) is important for initiating malignant transformation, and deregulation of the major signaling pathway nuclear factor of kappa B (NF-?B) by Tax represents a hallmark of HTLV-1 driven cancer. RESULTS:Here we found that Tax mutants which are defective in NF-?B signaling showed diminished protein expression levels compared to Tax wildtype in T-cells, whereas Tax transcript levels were comparable. Strikingly, constant activation of NF-?B signaling by the constitutive active mutant of inhibitor of kappa B kinase (IKK2, IKK-?), IKK2-EE, rescued protein expression of the NF-?B defective Tax mutants M22 and K1-10R and even increased protein levels of Tax wildtype in various T-cell lines while Tax transcript levels were only slightly affected. Using several Tax expression constructs, an increase of Tax protein occurred independent of Tax transcripts and independent of the promoter used. Further, Tax and M22 protein expression were strongly enhanced by 12-O-Tetradecanoylphorbol-13-Acetate [TPA; Phorbol 12-myristate 13-acetate (PMA)]/ ionomycin, inducers of NF-?B and cytokine signaling, but not by tumor necrosis factor alpha (TNF-?). On the other hand, co-expression of Tax with a dominant negative inhibitor of ?B, I?B?-DN, or specific inhibition of IKK2 by the compound ACHP, led to a vast decrease in Tax protein levels to some extent independent of Tax transcripts in transiently transfected and Tax-transformed T-cells. Cycloheximide chase experiments revealed that co-expression of IKK2-EE prolongs the half-life of M22, and constant repression of NF-?B signaling by I?B?-DN strongly reduces protein stability of Tax wildtype suggesting that NF-?B activity is required for Tax protein stability. Finally, protein expression of Tax and M22 could be recovered by NH4Cl and PYR-41, inhibitors of the lysosome and the ubiquitin-activating enzyme E1, respectively. CONCLUSIONS:Together, these findings suggest that Tax's capability to induce NF-?B is critical for protein expression and stabilization of Tax itself. Overall, identification of this novel positive feedback loop between Tax and NF-?B in T-cells improves our understanding of Tax-driven transformation.

SUBMITTER: Millen S

PROVIDER: S-EPMC7488018 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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A novel positive feedback-loop between the HTLV-1 oncoprotein Tax and NF-κB activity in T-cells.

Millen Sebastian S Meretuk Lina L Göttlicher Tim T Schmitt Sarah S Fleckenstein Bernhard B Thoma-Kress Andrea K AK

Retrovirology 20200910 1

<h4>Background</h4>Human T-cell leukemia virus type 1 (HTLV-1) infects primarily CD4<sup>+</sup> T-lymphocytes and evoques severe diseases, predominantly Adult T-Cell Leukemia/ Lymphoma (ATL/L) and HTLV-1-associated Myelopathy/ Tropical Spastic Paraparesis (HAM/TSP). The viral transactivator of the pX region (Tax) is important for initiating malignant transformation, and deregulation of the major signaling pathway nuclear factor of kappa B (NF-κB) by Tax represents a hallmark of HTLV-1 driven ca ...[more]

PMID: 32912211

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Project description:BackgroundRetroviruses HTLV-1 and HTLV-2 have homologous genomic structures but differ significantly in pathogenicity. HTLV-1 is associated with Adult T cell Leukemia (ATL), whereas infection by HTLV-2 has no association with neoplasia. Transformation of T lymphocytes by HTLV-1 is linked to the capacity of its oncoprotein Tax-1 to alter cell survival and cell cycle control mechanisms. Among these functions, Tax-1-mediated activation of cellular gene expression via the NF-κB pathway depends on Tax-1 post-translational modifications by ubiquitination and sumoylation. The Tax-2 protein of HTLV-2B (Tax-2B) is also modified by ubiquitination and sumoylation and activates the NF-κB pathway to a level similar to that of Tax-1. The present study aims to understand whether ubiquitination and sumoylation modifications are involved in Tax-2B-mediated activation of the NF-κB pathway.ResultsThe comparison of Tax-1 and Tax-2B lysine to arginine substitution mutants revealed conserved patterns and levels of ubiquitination with notable difference in the lysine usage for sumoylation. Neither Tax-1 nor Tax-2B ubiquitination and sumoylation deficient mutants could activate the NF-κB pathway and fusion of ubiquitin or SUMO-1 to the C-terminus of the ubiquitination and sumoylation deficient Tax-2B mutant strikingly restored transcriptional activity. In addition, ubiquitinated forms of Tax-2B colocalized with RelA and IKKγ in prominent cytoplasmic structures associated with the Golgi apparatus, whereas colocalization of Tax-2B with the RelA subunit of NF-κB and the transcriptional coactivator p300 in punctate nuclear structures was dependent on Tax-2B sumoylation, as previously observed for Tax-1.ConclusionsBoth Tax-1 and Tax-2 activate the NF-κB pathway via similar mechanisms involving ubiquitination and sumoylation. Therefore, the different transforming potential of HTLV-1 and HTLV-2 is unlikely to be related to different modes of activation of the canonical NF-κB pathway.

Dataset Information

A novel positive feedback-loop between the HTLV-1 oncoprotein Tax and NF-?B activity in T-cells.

Publications

A novel positive feedback-loop between the HTLV-1 oncoprotein Tax and NF-κB activity in T-cells.

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