Ubiquitination and sumoylation of the HTLV-2 Tax-2B protein regulate its NF-κB activity: a comparative study with the HTLV-1 Tax-1 protein

Marco Turci,Erica Diani,Carla Sampaio,Julie Lodewick,Umberto Bertazzoni,Oriano Marin,Maria Grazia Romanelli,Françoise Bex,Anne Sophie Rinaldi,Gianfranco Di Gennaro

doi:10.1186/1742-4690-9-102

Abstract

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.

Highlights

Retroviruses Human T-cell leukemia viruses type 1 (HTLV-1) and HTLV-2 have homologous genomic structures but differ significantly in pathogenicity
This study reveals that the transcriptional activity of the Tax-2 protein of HTLV-2B (Tax-2B) lysine to arginine substitution mutants and the ubiquitin and SUMO-1 fusions correlate with their ubiquitination and sumoylation status, suggesting a common mechanism of NF-κB activation for Tax-1 and Tax-2B
The unfused mutant K1-10iR was deficient for activation of the NF-κB pathway (1% of wild type unfused Tax-2B), ubiquitin or SUMO-1 fusion to this mutant increased its transcriptional activity by 21 and 17 fold as compared to their wild type Tax-2-Ub and Tax-2-SUMO controls, respectively. These results strongly suggest that both ubiquitination and sumoylation are directly involved in Tax-2B-mediated activation of the NF-κB pathway

Summary

Introduction

Retroviruses HTLV-1 and HTLV-2 have homologous genomic structures but differ significantly in pathogenicity. 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. Human T-cell leukemia viruses type 1 (HTLV-1) and type 2 (HTLV-2) share a common genomic structure but differ significantly in their pathogenic properties [1,2] This difference is generally attributed to the properties of their transactivating Tax proteins, Tax-1 and Tax-2, Because less is known about Tax-2, a comparative analysis between Tax-1 and Tax-2 is important in order to reach a better understanding of the differences in pathogenesis. Some HTLV-2 subtypes express shorter versions of Tax-2 (namely Tax-2A and Tax-2CG) which, contrary to Tax-2B, do not functionally inactivate p53 [10,19]

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