The HBZ-SP1 isoform of human T-cell leukemia virus type I represses JunB activity by sequestration into nuclear bodies

BACKGROUND: The human T-cell leukemia virus type I (HTLV-I) basic leucine-zipper factor (HBZ) has previously been shown to modulate transcriptional activity of Jun family members. The presence of a novel isoform of HBZ, termed HBZ-SP1, has recently been characterized in adult T-cell leukemia (ATL) cells and has been found to be associated with intense nuclear spots. In this study, we investigated the role of these nuclear bodies in the regulation of the transcriptional activity of JunB. RESULTS: Using fluorescence microscopy, we found that the HBZ-SP1 protein localizes to intense dots corresponding to HBZ-NBs and to nucleoli. We analyzed the relative mobility of the EGFP-HBZ-SP1 fusion protein using fluorescence recovery after photobleaching (FRAP) analysis and found that the deletion of the ZIP domain perturbs the association of the HBZ-SP1 protein to the HBZ-NBs. These data suggested that HBZ needs cellular partners, including bZIP factors, to form HBZ-NBs. Indeed, by cotransfection experiments in COS cells, we have found that the bZIP factor JunB is able to target delocalized form of HBZ (deleted in its nuclear localization subdomains) into the HBZ-NBs. We also show that the viral protein is able to entail a redistribution of JunB into the HBZ-NBs. Moreover, by transfecting HeLa cells (known to express high level of JunB) with a vector expressing HBZ-SP1, the sequestration of JunB to the HBZ-NBs inhibited its transcriptional activity. Lastly, we analyzed the nuclear distribution of HBZ-SP1 in the presence of JunD, a Jun family member known to be activated by HBZ. In this case, no NBs were detected and the HBZ-SP1 protein was diffusely distributed throughout the nucleoplasm. CONCLUSION: Our results suggest that HBZ-mediated sequestration of JunB to the HBZ-NBs may be causing the repression of JunB activity in vivo

Premature Activation of the SLX4 Complex by Vpr Promotes G2/M Arrest and Escape from Innate Immune Sensing

SummaryThe HIV auxiliary protein Vpr potently blocks the cell cycle at the G2/M transition. Here, we show that G2/M arrest results from untimely activation of the structure-specific endonuclease (SSE) regulator SLX4 complex (SLX4com) by Vpr, a process that requires VPRBP-DDB1-CUL4 E3-ligase complex. Direct interaction of Vpr with SLX4 induced the recruitment of VPRBP and kinase-active PLK1, enhancing the cleavage of DNA by SLX4-associated MUS81-EME1 endonucleases. G2/M arrest-deficient Vpr alleles failed to interact with SLX4 or to induce recruitment of MUS81 and PLK1. Furthermore, knockdown of SLX4, MUS81, or EME1 inhibited Vpr-induced G2/M arrest. In addition, we show that the SLX4com is involved in suppressing spontaneous and HIV-1-mediated induction of type 1 interferon and establishment of antiviral responses. Thus, our work not only reveals the identity of the cellular factors required for Vpr-mediated G2/M arrest but also identifies the SLX4com as a regulator of innate immunity

The BLM helicase is a new therapeutic target in multiple myeloma involved in replication stress survival and drug resistance

Multiple myeloma (MM) is a hematologic cancer characterized by accumulation of malignant plasma cells in the bone marrow. To date, no definitive cure exists for MM and resistance to current treatments is one of the major challenges of this disease. The DNA helicase BLM, whose depletion or mutation causes the cancer-prone Bloom’s syndrome (BS), is a central factor of DNA damage repair by homologous recombination (HR) and genomic stability maintenance. Using independent cohorts of MM patients, we identified that high expression of BLM is associated with a poor outcome with a significant enrichment in replication stress signature. We provide evidence that chemical inhibition of BLM by the small molecule ML216 in HMCLs (human myeloma cell lines) leads to cell cycle arrest and increases apoptosis, likely by accumulation of DNA damage. BLM inhibition synergizes with the alkylating agent melphalan to efficiently inhibit growth and promote cell death in HMCLs. Moreover, ML216 treatment re-sensitizes melphalan-resistant cell lines to this conventional therapeutic agent. Altogether, these data suggest that inhibition of BLM in combination with DNA damaging agents could be of therapeutic interest in the treatment of MM, especially in those patients with high BLM expression and/or resistance to melphalan

Rôle des protéines Taz et HBZ de HTLV-1 dans la régulation de la transcription virale et cellulaire

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

A tumor suppressive DNA translocase named FANCM

International audienceFANCM is named after Fanconi anemia (FA) complement group M. The clinical symptoms of FA include congenital abnormalities, pancytopenia, and cancer proneness. However, recent studies reveal that biallelic inactivation of FANCM does not cause the constellation of FA symptoms, but predisposes patients to cancer and infertility. FANCM is a tumor suppressor gene that encodes a conserved and structure-specific DNA translocase. It controls the outcome of homologous recombination and facilitates DNA replication across a variety of natural and chemically induced obstacles. This review details our current understanding of FANCM as a facilitator of the cellular functions of caretaker proteins, including FA, Bloom syndrome, and Ataxia telangiectasia and RAD3-related proteins, which collectively ensure the maintenance of chromosome stability during DNA replication

Ubiquitin-Independent Proteasomal Degradation of Fra-1 Is Antagonized by Erk1/2 Pathway-Mediated Phosphorylation of a Unique C-Terminal Destabilizer▿

Fra-1, a transcription factor that is phylogenetically and functionally related to the proto-oncoprotein c-Fos, controls many essential cell functions. It is expressed in many cell types, albeit with differing kinetics and abundances. In cells reentering the cell cycle, Fra-1 expression is transiently stimulated albeit later than that of c-Fos and for a longer time. Moreover, Fra-1 overexpression is found in cancer cells displaying high Erk1/2 activity and has been linked to tumorigenesis. One crucial point of regulation of Fra-1 levels is controlled protein degradation, the mechanism of which remains poorly characterized. Here, we have combined genetic, pharmacological, and signaling studies to investigate this process in nontransformed cells and to elucidate how it is altered in cancer cells. We report that the intrinsic instability of Fra-1 depends on a single destabilizer contained within the C-terminal 30 to 40 amino acids. Two serines therein, S252 and S265, are phosphorylated by kinases of the Erk1/2 pathway, which compromises protein destruction upon both normal physiological induction and tumorigenic constitutive activation of this cascade. Our data also indicate that Fra-1, like c-Fos, belongs to a small group of proteins that may, under certain circumstances, undergo ubiquitin-independent degradation by the proteasome. Our work reveals both similitudes and differences between Fra-1 and c-Fos degradation mechanisms. In particular, the presence of a single destabilizer within Fra-1, instead of two that are differentially regulated in c-Fos, explains the much faster turnover of the latter when cells traverse the G0/G1-to-S-phase transition. Finally, our study offers further insights into the signaling-regulated expression of the other Fos family proteins

The Central Region of Human T-Cell Leukemia Virus Type 1 Tax Protein Contains Distinct Domains Involved in Subunit Dimerization

The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) can form homodimers. Tax dimerization contributes to optimal Tax activity involved in transactivation of the HTLV-1 promoter. The mechanisms used to form specific Tax dimers are poorly understood because the domains that mediate such interactions have not been clearly characterized. Here we have used different approaches (the two-hybrid assay in yeast, the glutathione S-transferase pull-down assay, and the Spot method) to study Tax-Tax interactions. Our results indicate that the integrity of the sequence of Tax, except for the last 16 amino acids (residues 338 to 353), is critical, suggesting that Tax dimerization is dictated more by secondary structure than by primary structure. We were, however, able to delimit a central region involved in Tax self-association that encompasses the residues 127 to 228. This region can be divided into three subdomains of dimerization: DD1 (residues 127 to 146), DD2 (residues 181 to 194), and DD3 (residues 213 to 228). Moreover, the Tax mutants M22 (T130A and L131S) and M29 (K189A and R190S), with amino acid substitutions located in DD1 and DD2, respectively, were found to be impaired in Tax self-association

Ubiquitin-independent- versus ubiquitin-dependent proteasomal degradation of the c-Fos and Fra-1 transcription factors: Is there a unique answer?

International audienc

HBZ interacts with JunD and stimulates its transcriptional activity.

Human T-cell leukemia virus type I (HTLV-I) bZIP factor (HBZ) is a viral basic leucine zipper protein that was originally described as a partner of cAMP response element binding protein-2 and as a repressor of HTLV-I viral transcription. In addition, HBZ is able to interact with the activator protein-1 (AP-1) transcription factors c-Jun and JunB, the interaction with c-Jun leading to a transcriptional repression of AP-1-regulated genes. Here we show that HBZ also interacts with JunD in vitro and in vivo, and that this association occurs via the bZIP domain of the two proteins. Moreover, we show that HBZ can activate JunD-dependent transcription and that its amino-terminus is required

Arsenic/interferon-a triggered apoptosis in HTLV-I transformed cells is associated with proteasome mediated tax degradation and reversal of NF-κB activation

HTLV-I associated Adult T cell leukemia /lymphoma (ATL) is a malignancy of mature activated T cells resistant to conventional chemotherapy. The viral transactivator oncoprotein Tax plays a critical role in HTLV-I-induced transformation and resistance to apoptosis, through the activation of the NF-KB pathway by inducing IicB-a and IicE'-β degradation. We have previously shown that the combination of arsenic trioxide (As) and interferon-ot (IFN) is highly effective to induce cell cycle arrest and apoptosis in HTLVI positive cells compared to HTLV-1 negative T cells. We have also demonstrated that cell death induction by As and IFN in HTLV-I transformed cells is only partially dépendant upon caspase activation and is not associated with modulation of bcl-2, bax or p 53 expression. In this study, we show that the combination of As and IFN induces the downregulation of Tax by the proteasome in both HTLV-I transformed cells and in T-cdls transiently transfected with Tax. This is associated with an upregulation of iKB-a, tofiβ and iKB-e through inhibition of their proteasomal degradation. Furthermore, As/EN treatment inhibits NF-KB reporter gene induction after Tax transfection and results in a sharp decrease in RelA DNA binding NF-KB complexes in HTLV-I transformed cells due to the cytoplasmic retention of RelA. Although Tax was previously shown to bind proteasome subunits to enhance lKB-a degradation, using kinetic studies we showed that As alone increases lKB-a level before the occurrence of Tax down-regulation. This sugge sts that As and As/IFN alters the proteasome function qualitatively to differentially enhance Tax degradation and inhibit lKB-a degradation. Such specific targeting of the viral oncoprotein by IFN/As treatment, reminiscent of As targeting of PML/RARa in acute promyelocytic leukemia, provides strong rational for combined IFN/As therapy in ATL patients. Indeed, preliminary results of a phase II clinical trial in relapsed/refractory ATL patients are encouraging suggesting the possibility of introducing As in the first line therapy of ATL.SCOPUS: ar.jinfo:eu-repo/semantics/publishe