Move or Die: the Fate of the Tax Oncoprotein of HTLV-1

The HTLV-1 Tax protein both activates viral replication and is involved in HTLV-1-mediated transformation of T lymphocytes. The transforming properties of Tax include altering the expression of select cellular genes via activation of cellular pathways and perturbation of both cell cycle control mechanisms and apoptotic signals. The recent discovery that Tax undergoes a hierarchical sequence of posttranslational modifications that control its intracellular localization provides provocative insights into the mechanisms regulating Tax transcriptional and transforming activities

Comparative analysis of HTLV-1 and HTLV-2 post-translational modifications of Tax proteins in relation to their intracellular localization and activation of gene expression

Poster presentatio

Crystal Structure of the Cul2-Rbx1-EloBC-VHL Ubiquitin Ligase Complex

Cullin RING E3 ubiquitin ligases (CRLs) function in the ubiquitin proteasome system to catalyze the transfer of ubiquitin from E2 conjugating enzymes to specific substrate proteins. CRLs are large dynamic complexes and attractive drug targets for the development of small-molecule inhibitors and chemical inducers of protein degradation. The atomic details of whole CRL assembly and interactions that dictate subunit specificity remain elusive. Here we present the crystal structure of a pentameric CRL2VHL complex, composed of Cul2, Rbx1, Elongin B, Elongin C, and pVHL. The structure traps a closed state of full-length Cul2 and a new pose of Rbx1 in a trajectory from closed to open conformation. We characterize hotspots and binding thermodynamics at the interface between Cul2 and pVHL-EloBC and identify mutations that contribute toward a selectivity switch for Cul2 versus Cul5 recognition. Our findings provide structural and biophysical insights into the whole Cul2 complex that could aid future drug targeting

Filamins Regulate Cell Spreading and Initiation of Cell Migration

Mammalian filamins (FLNs) are a family of three large actin-binding proteins. FLNa, the founding member of the family, was implicated in migration by cell biological analyses and the identification of FLNA mutations in the neuronal migration disorder periventricular heterotopia. However, recent knockout studies have questioned the relevance of FLNa to cell migration. Here we have used shRNA-mediated knockdown of FLNa, FLNb or FLNa and FLNb, or, alternatively, acute proteasomal degradation of all three FLNs, to generate FLN-deficient cells and assess their ability to migrate. We report that loss of FLNa or FLNb has little effect on migration but that knockdown of FLNa and FLNb, or proteolysis of all three FLNs, impairs migration. The observed defect is primarily a deficiency in initiation of motility rather than a problem with maintenance of locomotion speed. FLN-deficient cells are also impaired in spreading. Re-expression of full length FLNa, but not re-expression of a mutated FLNa lacking immunoglobulin domains 19 to 21, reverts both the spreading and the inhibition of initiation of migration

NRP/Optineurin Cooperates with TAX1BP1 to Potentiate the Activation of NF-κB by Human T-Lymphotropic Virus Type 1 Tax Protein

Nuclear factor (NF)-κB is a major survival pathway engaged by the Human T-Lymphotropic Virus type 1 (HTLV-1) Tax protein. Tax1 activation of NF-κB occurs predominantly in the cytoplasm, where Tax1 binds NF-κB Essential Modulator (NEMO/IKKγ) and triggers the activation of IκB kinases. Several independent studies have shown that Tax1-mediated NF-κB activation is dependent on Tax1 ubiquitination. Here, we identify by co-immunoprecipitation assays NEMO-Related Protein (NRP/Optineurin) as a binding partner for Tax1 in HTLV-1 infected and Tax1/NRP co-expressing cells. Immunofluorescence studies reveal that Tax1, NRP and NEMO colocalize in Golgi-associated structures. The interaction between Tax1 and NRP requires the ubiquitin-binding activity of NRP and the ubiquitination sites of Tax1. In addition, we observe that NRP increases the ubiquitination of Tax1 along with Tax1-dependent NF-κB signaling. Surprisingly, we find that in addition to Tax1, NRP interacts cooperatively with the Tax1 binding protein TAX1BP1, and that NRP and TAX1BP1 cooperate to modulate Tax1 ubiquitination and NF-κB activation. Our data strongly suggest for the first time that NRP is a critical adaptor that regulates the assembly of TAX1BP1 and post-translationally modified forms of Tax1, leading to sustained NF-κB activation

SUMO-Interacting Motifs of Human TRIM5α are Important for Antiviral Activity

Human TRIM5α potently restricts particular strains of murine leukemia viruses (the so-called N-tropic strains) but not others (the B- or NB-tropic strains) during early stages of infection. We show that overexpression of SUMO-1 in human 293T cells, but not in mouse MDTF cells, profoundly blocks N-MLV infection. This block is dependent on the tropism of the incoming virus, as neither B-, NB-, nor the mutant R110E of N-MLV CA (a B-tropic switch) are affected by SUMO-1 overexpression. The block occurred prior to reverse transcription and could be abrogated by large amounts of restricted virus. Knockdown of TRIM5α in 293T SUMO-1-overexpressing cells resulted in ablation of the SUMO-1 antiviral effects, and this loss of restriction could be restored by expression of a human TRIM5α shRNA-resistant plasmid. Amino acid sequence analysis of human TRIM5α revealed a consensus SUMO conjugation site at the N-terminus and three putative SUMO interacting motifs (SIMs) in the B30.2 domain. Mutations of the TRIM5α consensus SUMO conjugation site did not affect the antiviral activity of TRIM5α in any of the cell types tested. Mutation of the SIM consensus sequences, however, abolished TRIM5α antiviral activity against N-MLV. Mutation of lysines at a potential site of SUMOylation in the CA region of the Gag gene reduced the SUMO-1 block and the TRIM5α restriction of N-MLV. Our data suggest a novel aspect of TRIM5α-mediated restriction, in which the presence of intact SIMs in TRIM5α, and also the SUMO conjugation of CA, are required for restriction. We propose that at least a portion of the antiviral activity of TRIM5α is mediated through the binding of its SIMs to SUMO-conjugated CA

Distinct functions of HTLV-1 Tax1 from HTLV-2 Tax2 contribute key roles to viral pathogenesis

While the human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATL), to date, its close relative HTLV-2 is not associated with ATL or other types of malignancies. Accumulating evidence shows that HTLV-1 Tax1 and HTLV-2 Tax2 have many shared activities, but the two proteins have a limited number of significantly distinct activities, and these distinctions appear to play key roles in HTLV-1 specific pathogenesis. In this review, we summarize the functions of Tax1 associated with cell survival, cell proliferation, persistent infection as well as pathogenesis. We emphasize special attention to distinctions between Tax1 and Tax2

Molecular Tuning of Filamin A Activities in the Context of Adhesion and Migration

International audienceThe dynamic organization of actin cytoskeleton meshworks relies on multiple actinbinding proteins endowed with distinct actin-remodeling activities. Filamin A is a large multi-domain scaffolding protein that cross-links actin filaments with orthogonal orientation in response to various stimuli. As such it plays key roles in the modulation of cell shape, cell motility, and differentiation throughout development and adult life. The essentiality and complexity of Filamin A is highlighted by mutations that lead to a variety of severe human disorders affecting multiple organs. One of the most conserved activity of Filamin A is to bridge the actin cytoskeleton to integrins, thereby maintaining the later in an inactive state. We here review the numerous mechanisms cells have developed to adjust Filamin A content and activity and focus on the function of Filamin A as a gatekeeper to integrin activation and associated adhesion and motility

Post-translational modifications of the tax oncoprotein of human T-cell leukemia virus control cytoplasmic and nuclear steps in tax-mediated activation of the NF-κB pathway

SCOPUS: no.jinfo:eu-repo/semantics/publishe