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

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

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

Ubiquitin-mediated proteasomal degradation in normal and malignant hematopoiesis.

International audienceUnderstanding the molecular mechanisms controlling normal hematopoietic differentiation is critical to develop new treatments for blood diseases and to manipulate stem cells. Despite the identification of many players in hematopoiesis, the molecular mechanisms controlling hematopoietic differentiation remain poorly understood. Due to a number of recent findings, the targeting of regulators of hematopoiesis to proteasomal degradation might be an important step in control of this developmental program

Filamins but Not Janus Kinases Are Substrates of the ASB2α Cullin-Ring E3 Ubiquitin Ligase in Hematopoietic Cells

International audienceThe ASB2α protein is the specificity subunit of an E3 ubiquitin ligase complex involved in hematopoietic differentiation and is proposed to exert its effects by regulating the turnover of specific proteins. Three ASB2α substrates have been described so far: the actin-binding protein filamins, the Mixed Lineage Leukemia protein, and the Janus kinases 2 and 3. To determine the degradation of which substrate drives ASB2α biological effects is crucial for the understanding of ASB2α functions in hematopoiesis. Here, we show that neither endogenous nor exogenously expressed ASB2α induces degradation of JAK proteins in hematopoietic cells. Furthermore, we performed molecular modeling to generate the first structural model of an E3 ubiquitin ligase complex of an ASB protein bound to one of its substrates

Cullin 5-RING E3 ubiquitin ligases, new therapeutic targets?

International audienceUbiquitylation is a reversible post-translational modification of proteins that controls a myriad of functions and cellular processes. It occurs through the sequential action of three distinct enzymes. E3 ubiquitin ligases (E3s) play the role of conductors of the ubiquitylation pathway making them attractive therapeutic targets. This review is dedicated to the largest family of multimeric E3s, the Cullin-RING E3 (CRL) family and more specifically to cullin 5 based CRLs that remains poorly characterized

Stable Ubiquitination of Human T-Cell Leukemia Virus Type 1 Tax Is Required for Proteasome Binding

Human T-cell leukemia virus type 1 (HTLV-1) is the retrovirus responsible for adult T-cell leukemia and HTLV-1-associated myelopathy. Adult T-cell leukemia development is mainly due to the ability of the viral oncoprotein Tax to promote T-cell proliferation, whereas the appearance of HTLV-1-associated myelopathy involves the antigenic properties of Tax. Understanding the events regulating the intracellular level of Tax is therefore an important issue. How Tax is degraded has not been determined, but it is known that Tax binds to proteasomes, the major sites for degradation of intracellular proteins, generally tagged through polyubiquitin conjugation. In this study, we investigated the relationship between Tax, ubiquitin, and proteasomes. We report that mono- and polyubiquitinated Tax proteins can be recovered from both transfected 293T cells and T lymphocytes. We also show that lysine residues located in the carboxy-terminal domain of Tax are the principal targets of this process. Remarkably, we further demonstrate that mutation of lysine residues in the C-terminal part of Tax, which massively reduces Tax ubiquitination, impairs proteasome binding, and conversely, that a Tax mutant that binds poorly to this particle (M22) is faintly ubiquitinated, suggesting that Tax ubiquitination is required for association with cellular proteasomes. Finally, we document that comparable amounts of ubiquitinated species were found whether proteasome activities were inhibited or not, providing evidence that they are not directly addressed to proteasomes for degradation. These findings indicate that although it is ubiquitinated and binds to proteasomes, Tax is not massively degraded via the ubiquitin-proteasome pathway and therefore reveal that Tax conjugation to ubiquitin mediates a nonproteolytic function