The Experts below are selected from a list of 5562 Experts worldwide ranked by ideXlab platform
John N. Brady - One of the best experts on this subject based on the ideXlab platform.
-
Human T-Lymphotropic Virus Type 1 Tax Protein Complexes with P-TEFb and Competes for Brd4 and 7SK snRNP/HEXIM1 Binding
Journal of Virology, 2010Co-Authors: Won-kyung Cho, M Jang, Keven Huang, Cynthia A. Pise-masison, John N. BradyAbstract:Positive transcription elongation factor b (P-TEFb) plays an important role in stimulating RNA polymerase II elongation for viral and cellular gene expression. P-TEFb is found in cells in either an active, low-molecular-weight (LMW) form or an inactive, high-molecular-weight (HMW) form. We report here that human T-lymphotropic virus type 1 (HTLV-1) Tax interacts with the cyclin T1 subunit of P-TEFb, forming a distinct Tax/P-TEFb LMW complex. We demonstrate that Tax can play a role in regulating the amount of HMW complex present in the cell by decreasing the binding of 7SK snRNP/HEXIM1 to P-TEFb. This is seen both in vitro using purified Tax Protein and in vivo in cells transduced with Tax expression constructs. Further, we find that a peptide of cyclin T1 spanning the Tax binding domain inhibits the ability of Tax to disrupt HMW P-TEFb complexes. These results suggest that the direct interaction of Tax with cyclin T1 can dissociate P-TEFb from the P-TEFb/7SK snRNP/HEXIM1 complex for activation of the viral long terminal repeat (LTR). We also show that Tax competes with Brd4 for P-TEFb binding. Chromatin immunoprecipitation (ChIP) assays demonstrated that Brd4 and P-TEFb are associated with the basal HTLV-1 LTR, while Tax and P-TEFb are associated with the activated template. Furthermore, the knockdown of Brd4 by small interfering RNA (siRNA) activates the HTLV-1 LTR promoter, which results in an increase in viral expression and production. Our studies have identified Tax as a regulator of P-TEFb that is capable of affecting the balance between its association with the large inactive complex and the small active complex.
-
nrp optineurin cooperates with Tax1bp1 to potentiate the activation of nf kappab by human t lymphotropic virus type 1 Tax Protein
PLOS Pathogens, 2009Co-Authors: Chloé Journo, Frédégonde About, Frederic Tangy, Philippe V Afonso, John N. Brady, Alain Israel, Josina Cortereal Filipe, Sebastien Chevalier, David N Flynn, Pierre-olivier VidalainAbstract:Nuclear factor (NF)-kappaB is a major survival pathway engaged by the Human T-Lymphotropic Virus type 1 (HTLV-1) Tax Protein. Tax1 activation of NF-kappaB occurs predominantly in the cytoplasm, where Tax1 binds NF-kappaB Essential Modulator (NEMO/IKKgamma) and triggers the activation of IkappaB kinases. Several independent studies have shown that Tax1-mediated NF-kappaB 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-kappaB 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-kappaB 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-kappaB activation.
-
NRP/Optineurin Cooperates with Tax1BP1 to potentiate the activation of NF-kappaB by human T-lymphotropic virus type 1 Tax Protein.
PLoS Pathogens, 2009Co-Authors: Chloé Journo, Josina Filipe, Frédégonde About, Sébastien A. Chevalier, Frederic Tangy, Philippe V Afonso, John N. Brady, Alain Israel, David Flynn, Pierre-olivier VidalainAbstract:Nuclear factor (NF)-kappaB is a major survival pathway engaged by the Human T-Lymphotropic Virus type 1 (HTLV-1) Tax Protein. Tax1 activation of NF-kappaB occurs predominantly in the cytoplasm, where Tax1 binds NF-kappaB Essential Modulator (NEMO/IKKgamma) and triggers the activation of IkappaB kinases. Several independent studies have shown that Tax1-mediated NF-kappaB 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-kappaB 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-kappaB 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-kappaB activation.
-
The Tax Protein from the primate T-cell lymphotropic virus type 3 is expressed in vivo and is functionally related to HTLV-1 Tax rather than HTLV-2 Tax.
Oncogene, 2006Co-Authors: Sébastien A. Chevalier, Cynthia A. Pise-masison, Laurent Meertens, Sara Calattini, Hyeon Ung Park, A A Alhaj, M Zhou, Antoine Gessain, Fatah Kashanchi, John N. BradyAbstract:The Tax Protein from the primate T-cell lymphotropic virus type 3 is expressed in vivo and is functionally related to HTLV-1 Tax rather than HTLV-2 Tax
-
Human T-lymphotropic virus type I Tax Protein utilizes distinct pathways for p53 inhibition that are cell type-dependent.
The Journal of biological chemistry, 2001Co-Authors: Cynthia A. Pise-masison, Renaud Mahieux, Michael F. Radonovich, Hua Jiang, John N. BradyAbstract:p53 plays a pivotal role in transmitting signals from many forms of genotoxic stress to genes and factors that control the cell cycle and apoptosis. We have previously shown that the human T-lymphotropic virus type I Tax Protein can inhibit p53 function. Recently we reported that Tax inhibits p53 function in Jurkat cells and mouse embryo fibroblasts through a mechanism involving the nuclear factor kappa B pathway and correlates with phosphorylation on serines 15 and 392 of p53. However, several groups have also observed a mechanism that correlates with p300 binding of Tax. To address this controversy and to determine the mechanism by which Tax inhibits p53 function, we examined the activation functions of Tax required for p53 inhibition. In HeLa and H1299 cells the cAMP-response element-binding Protein/activating transcription factor activation function is essential, as demonstrated by the Tax mutants M47 and K88A. In addition, expression of exogenous p300 in H1299 cells allows full recovery of p53 transactivation in the presence of Tax. Consistent with p300 being a limiting factor in H1299, Saos-2, and HeLa cells, we found that the level of endogenous p300 is relatively low in these cells compared with Jurkat cells or the human T-lymphotropic virus type I-infected C81 and MT2 cells. Thus our data suggests that Tax utilizes distinct mechanisms to inhibit p53 function that are cell type-dependent.
Lee Ratner - One of the best experts on this subject based on the ideXlab platform.
-
the Tax Protein of human t cell leukemia virus type 1 mediates the transactivation of the c sis platelet derived growth factor b promoter through interactions with the zinc finger transcription factors sp1 and ngfi a egr 1
Journal of Biological Chemistry, 1997Co-Authors: Samuel R. Trejo, William E. Fahl, Lee RatnerAbstract:Transcriptional up-regulation of the c-sis/platelet-derived growth factor-B (PDGF-B) proto-oncogene by the Tax Protein of human T-cell leukemia virus type 1 has been implicated as one possible mechanism of cellular transformation by human T-cell leukemia virus type 1. In previous work, we identified an essential site in the c-sis/PDGF-B promoter, Tax-responsive element 1 (TRE1), necessary for transactivation by Tax. We also identified Sp1, Sp3, and NGFI-A/Egr-1 as the primary nuclear transcription factors binding to TRE1 which mediate Tax responsiveness. In the present work, we have investigated the mechanism(s) whereby Tax transactivates the c-sis/PDGF-B proto-oncogene. In vitro transcription assays showed that Tax was able to significantly increase the transcriptional activity of a template containing the -257 to +74 region of the c-sis/PDGF-B promoter. Electrophoretic mobility shift assay analysis showed that Tax increased the DNA binding activity of both Sp1 and NGFI-A/Egr-1 using a TRE1 probe. Analysis of Tax mutants showed that two mutants, IEXC29S and IEXL320G, were unable to significantly transactivate the c-sis/PDGF-B promoter. Finally, co-immunoprecipitation analysis revealed that Tax is able to stably bind to both Sp1 and NGFI-A/Egr-1. Interestingly, co-immunoprecipitation analysis also revealed that Tax mutant IEXC29S is unable to interact with NGFI-A/Egr-1, whereas Tax mutant IEXL320G is able to interact with NGFI-A/Egr-1.
-
c-sis/PDGF-B Promoter Transactivation by the Tax Protein of Human T-cell Leukemia Virus Type 1
The Journal of biological chemistry, 1996Co-Authors: Samuel R. Trejo, William E. Fahl, Lee RatnerAbstract:The human c-sis proto-oncogene promoter is transactivated by the human T-cell leukemia virus type 1 Tax Protein in human Jurkat T-cells. Transactivation was >7-fold in Jurkat cells stably expressing the Tax Protein (Jurkat-Tax) than in Jurkat E6.1 cells and was further enhanced in Jurkat-Tax cells stimulated with 12-O-tetradecanoylphorbol-13-acetate and the calcium ionophore, ionomycin. Deletion analysis showed that a 167-base pair promoter fragment retained full Tax responsiveness. Insertion of this minimal Tax-responsive region into a heterologous, minimal promoter resulted in approximately a 7-fold increase of transcriptional activation in the presence of Tax. Linker-scanning insertion analysis of this region identified Tax-responsive elements at nucleotides -64 to -45 (TRE1) and -34 to -15 (TATA box region). TRE1 contains a consensus binding site for the Sp family of transcription factors. The TATA box region corresponds to the TATA box and its 3'-neighboring sequence. Gel-shift and antibody supershift analysis of TRE1-binding Proteins in unstimulated Jurkat E6.1 and Jurkat-Tax nuclear extracts identified Sp1 and Sp3 as the main TRE1 binding factors. Nuclear extracts from stimulated Jurkat E6.1 and Jurkat-Tax cells identified an additional TRE1 binding factor, Egr-1. These studies define a novel mechanism whereby Tax transactivates the c-sis promoter.
-
c sis pdgf b promoter transactivation by the Tax Protein of human t cell leukemia virus type 1
Journal of Biological Chemistry, 1996Co-Authors: Samuel R. Trejo, William E. Fahl, Lee RatnerAbstract:The human c-sis proto-oncogene promoter is transactivated by the human T-cell leukemia virus type 1 Tax Protein in human Jurkat T-cells. Transactivation was >7-fold in Jurkat cells stably expressing the Tax Protein (Jurkat-Tax) than in Jurkat E6.1 cells and was further enhanced in Jurkat-Tax cells stimulated with 12-O-tetradecanoylphorbol-13-acetate and the calcium ionophore, ionomycin. Deletion analysis showed that a 167-base pair promoter fragment retained full Tax responsiveness. Insertion of this minimal Tax-responsive region into a heterologous, minimal promoter resulted in approximately a 7-fold increase of transcriptional activation in the presence of Tax. Linker-scanning insertion analysis of this region identified Tax-responsive elements at nucleotides -64 to -45 (TRE1) and -34 to -15 (TATA box region). TRE1 contains a consensus binding site for the Sp family of transcription factors. The TATA box region corresponds to the TATA box and its 3'-neighboring sequence. Gel-shift and antibody supershift analysis of TRE1-binding Proteins in unstimulated Jurkat E6.1 and Jurkat-Tax nuclear extracts identified Sp1 and Sp3 as the main TRE1 binding factors. Nuclear extracts from stimulated Jurkat E6.1 and Jurkat-Tax cells identified an additional TRE1 binding factor, Egr-1. These studies define a novel mechanism whereby Tax transactivates the c-sis promoter.
Masahiro Fujii - One of the best experts on this subject based on the ideXlab platform.
-
human t cell leukemia virus type 2 htlv 2 Tax Protein transforms a rat fibroblast cell line but less efficiently than htlv 1 Tax
Journal of Virology, 2002Co-Authors: Keiichi Endo, William W. Hall, Akira Hirata, Kousuke Iwai, Mamoru Sakurai, Masaya Fukushi, Masayasu Oie, Masaya Higuchi, Fumitake Gejyo, Masahiro FujiiAbstract:Human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 are retroviruses with similar biological properties. Whereas HTLV-1 is the causative agent of an aggressive T-cell leukemia, HTLV-2 has been associated with only a few cases of lymphoproliferative disorders. Tax1 and Tax2 are the transcriptional activators of HTLV-1 and HTLV-2, respectively. Here we show that Tax2 transformed a Rat-1 fibroblast cell line to form colonies in soft agar, but the size and number of the colonies were lower than those of Tax1. Use of a chimeric Tax Protein showed that the C-terminal amino acids 300 to 353 were responsible for the high transforming activity of Tax1. Activation of cellular genes by Tax1 through transcription factor NF-κB is reportedly essential for the transformation of Rat-1 cells. Tax2 also activated the transcription through NF-κB in Rat-1 cells, and such activity was equivalent to that induced by Tax1. Thus, the high transforming activity of Tax1 is mediated by mechanisms other than NF-κB activation. Our results showed that Tax2 has a lower transforming activity than Tax1 and suggest that the high transforming activity of Tax1 is involved in the leukemogenic property of HTLV-1.
-
human t cell leukemia virus type 1 Tax Protein activates transcription through ap 1 site by inducing dna binding activity in t cells
Virology, 2001Co-Authors: Masayasu Oie, Kousuke Iwai, Naoki Mori, Naoki Yamamoto, Masahiro FujiiAbstract:Abstract Human T-cell leukemia virus type 1 (HTLV-1) Tax Protein induces the expression of various family members of the transcription factor AP-1, such as c-Jun, JunD, c-Fos, and Fra-1, at the level of RNA expression in T cells. We examined the activity of Tax in transcription through AP-1-binding sites (AP-1 site) in T cells. Transient transfection studies showed that Tax activated the expression of a luciferase gene regulated by two copies of an AP-1 site in the human Jurkat T-cell line. Tax activates the expression of viral and cellular genes through two different enhancers: a cAMP-responsive (CRE)-like element and a κB element. Two Tax mutants differentially activated expression of these two elements. Tax703 preferentially activated the κB element but not the CRE-like one, whereas TaxM22 showed the reverse. In addition, Tax703 and Tax, but not TaxM22, converted cell growth of a mouse T-cell line from being interleukin (IL)-2-dependent to being IL-2-independent. Unlike the wild-type Tax, Tax703 and TaxM22 only weakly activated the AP-1 site in the T-cell line. Thus, Tax seems to activate the AP-1 site via mechanisms distinct from those of κB or CRE-like elements, and the activation of the AP-1 site is dispensable for IL-2-independent growth of CTLL-2. Electrophoretic mobility shift assays showed that Tax induced strong binding activity to an AP-1 site in CTLL-2, whereas Tax703 did not, indicating that the induction of binding activity to the AP-1 site is essential for the transcriptional activation by Tax. The binding complex induced by Tax in CTLL-2 contained JunD and Fra-2. Other AP-1 Proteins were undetectable. Activation of transcription through the AP-1 site in Jurkat cells by JunD and/or Fra-2 was weak. c-Jun, JunB, and c-Fos activation was greater, although the level was still less than that with Tax. Thus, the induction of AP-1 mRNA by Tax may not be sufficient for a complete activation of AP-1 site by Tax. Our results suggest that Tax activates the transcription of cellular genes with AP-1 sites by inducing the DNA-binding activity of AP-1 Proteins in T cells, a mechanism distinct from those of CRE-like and κB elements.
-
Human T-cell leukemia virus type 1 Tax Protein transforms rat fibroblasts via two distinct pathways.
Journal of virology, 1997Co-Authors: Kayoko Matsumoto, Hirotoshi Shibata, Jun-ichi Fujisawa, Hirokazu Inoue, Akira Hakura, Tomonori Tsukahara, Masahiro FujiiAbstract:The human T-cell leukemia virus type 1 (HTLV-1) Tax Protein activates the transcription of several cellular genes. This function is thought to play a critical role in the Tax-dependent transformation step in HTLV-1 leukemogenesis. Tax activates transcription via three enhancers: the cyclic AMP response element (CRE)-like sequence, the kappaB element, and the CArG box. Their involvement in the transformation of rat fibroblasts by Tax was examined by colony formation of Rat-1 cells in soft agar and Ras cooperative focus formation of rat embryo fibroblasts (REF). Among Tax mutants, those retaining activity for the CArG box transformed REF like wild-type Tax, while those inactive for the CArG box did not. Thus, the activation of the CArG box pathway is essential for the transformation of REF by Tax. In contrast, activation of the kappaB element correlated with the transformation of Rat-1 by Tax. These results show that Tax transforms rat fibroblasts via two distinct pathways.
Yoko Aida - One of the best experts on this subject based on the ideXlab platform.
-
A Mutant Form of the Tax Protein of Bovine Leukemia Virus (BLV), with Enhanced Transactivation Activity, Increases Expression and Propagation of BLV In Vitro but Not In Vivo
Journal of virology, 2003Co-Authors: Shigeru Tajima, Masahiko Takahashi, Shin-nosuke Takeshima, Satoru Konnai, Shan Ai Yin, Shinobu Watarai, Yoshimasa Tanaka, Misao Onuma, Kosuke Okada, Yoko AidaAbstract:In a previous study, we identified an interesting mutant form of the Tax Protein of bovine leukemia virus (BLV), designated D247G. This mutant Protein strongly transactivated the long terminal repeat of BLV and was also able to transactivate the cellular proto-oncogene c-fos. This finding suggested that BLV that encode the mutant Protein might propagate and induce lymphoma more efficiently than wild-type BLV. To characterize the effects of the strong transactivation activity of the mutant Tax Protein, we constructed an infectious molecular clone of BLV that encoded D247G and examined the replication and propagation of the virus in vitro and in vivo. Cultured cells were transfected with the wild-type and mutant BLV, and then levels of viral Proteins and particles and the propagation of viruses were compared. As expected, in vitro, mutant BLV produced more viral Proteins and particles and was transmitted very effectively. We injected the wild-type and mutant BLV into sheep, which are easily infected with BLV, and monitored the proportion of BLV-positive cells in the blood and the expression of BLV RNA for 28 weeks. By contrast to the results of our analyses in vitro, we found no significant difference in the viral load or the expression of viral RNA between sheep inoculated with wild-type or mutant BLV. Our observations indicate that the mutant D247G Tax Protein does not enhance the expansion of BLV and that there might be a dominant mechanism for regulation of the expression of BLV in vivo.
-
Mutant Tax Protein from Bovine Leukemia Virus with Enhanced Ability To Activate the Expression of c-fos
Journal of virology, 2002Co-Authors: Shigeru Tajima, Yoko AidaAbstract:Bovine leukemia virus (BLV) is the etiologic agent of enzootic bovine leukosis. We previously identified several mutants of the BLV Tax Protein with an ability to transactivate transcription via the BLV enhancer that is significantly greater than that of the wild-type Tax Protein. Moreover, the mutant Proteins also activated other viral enhancers, such as the enhancer of human T-cell leukemia virus type 1, which cannot be activated by wild-type BLV Tax. In this study, we demonstrated that the mutant Proteins but not wild-type Protein activate the upstream sequence of the human c-fos gene, which contains two major cis-acting elements, the CArG box and cyclic AMP-responsive element (CRE) motif. The mutant Protein also strongly increased levels of endogenous c-fos mRNA in both human and bovine cell lines. On the other hand, the wild-type Tax Protein has no activity to activate the expression of human c-fos, indicating that wild-type BLV Tax might discriminate between human and bovine c-fos promoter sequences. Deletion and point-mutational analysis of the cis-acting elements revealed that both the CArG box and the CRE motif were indispensable for the activation of c-fos by the mutant BLV Tax Protein. Our results suggest that the mutant BLV Tax Proteins might not only have the ability to enhance the production of virus particles but might also have increased ability to induce leukemia.
-
The Region between Amino Acids 245 and 265 of the Bovine Leukemia Virus (BLV) Tax Protein Restricts Transactivation Not Only via the BLV Enhancer but Also via Other Retrovirus Enhancers
Journal of virology, 2000Co-Authors: Shigeru Tajima, Yoko AidaAbstract:Bovine leukemia virus (BLV) is the etiologic agent of enzootic bovine leukosis (EBL), which is the most common neoplastic disease of cattle, and it is often associated with persistent lymphocytosis, which is characterized by an increased number of normal B lymphocytes and the subsequent development of B-cell leukemia or lymphosarcoma after a long latency period (9). Sheep that are experimentally inoculated with BLV are readily infected, and some develop B-cell tumors at higher frequencies and after a shorter latency period than naturally inoculated cattle (3, 15). BLV is closely related to human T-cell leukemia virus type 1 (HTLV-1), which is the causative agents of adult T-cell leukemia and a chronic neurological disorder known as tropical spastic paraparesis or HTLV-1-associated myelopathy (10). BLV and HTLV constitute a unique subgroup within the retrovirus family, being characterized by similar genomic organizations, similar strategies for gene expression, and similar pathologies. In addition to the structural Proteins Gag, Pol, and Env, these viruses encode at least two regulatory Proteins, namely, Tax and Rex, in the pX region located between the env gene and the 3′ long terminal repeat (LTR). The Tax Protein acts on a triplicate 21-bp motif known as the Tax-responsive element (TxRE) in the U3 region of the 5′ LTR, and it stimulates transactivation of the virus genome (13, 16, 20, 52). The TxRE consists of a cyclic AMP-response element (CRE)-like sequence, and it has been suggested that Tax binds indirectly to this element through cellular factors, such as members of the CREB/ATF family of basic-leucine zipper Proteins which have been shown to bind to the CRE-like sequence (6, 43). The Tax Protein of HTLV-1 is also known to modulate the expression of many cellular genes that are related to regulation of cell growth (61), but little is known about the Tax Protein of BLV (27). The Tax Proteins of BLV and HTLV-1 can cooperate with the Ha-Ras oncoProtein to induce the full transformation of primary rat embryo fibroblasts (34, 54). These findings indicate that the Tax Protein is a key contributor to the oncogenic potential, as well as a key Protein in the replication of the virus. The Rex Protein interacts with the Rex-responsive element in the 3′ R regions of the BLV and HTLV-1 mRNAs and enhances the cytoplasmic accumulation of singly spliced and unspliced transcripts. This enhancement leads to an increase in the production of structural Proteins and to a decrease in the level of the doubly spliced Tax-rex mRNA (14, 42). RNA viruses have high rates of variation in nucleotide sequence, as frequently observed in members of the lentivirus group, such as human immunodeficiency virus (HIV), and such variation is important for viral survival during immunological attack by the host's immune system. However, in BLV and HTLV-1, the genetic variability appears to be limited in vivo (12, 21, 57, 58). Moreover, it is difficult to detect transcripts of the BLV and HTLV genomes in fresh tumor cells or in fresh peripheral blood lymphocytes (PBL) from infected individuals (18, 29). These findings suggest that the BLV-HTLV subgroup might exploit a strict mechanism for control of the expression of viral Proteins throughout the course of leukemogenesis in order to evade the host's immunosurveillance system. However, we do not yet know how viral expression is inhibited in vivo. The increased expression of BLV and HTLV-1 mRNAs can be induced by several activators of lymphocytes, such as fetal calf serum, lipopolysaccharides, and phorbol esters, after culture of lymphocytes in vitro (1, 24, 32, 33). Recent findings also indicate that interleukin-2 (IL-2) activates BLV mRNA and enhances levels of viral Proteins, while IL-10 inhibits detection of BLV mRNA (39). Furthermore, phosphorylation of HTLV-1 Tax is critical for the transactivation function of Tax, and the extent of such phosphorylation in human lymphocytes is increased by treatment of cells with phorbol esters (5, 17). We showed previously that BLV-infected cattle retain a full-length proviral genome throughout the course of their disease (44), in sharp contrast to the high frequencies (30 to 50%) of deletions in proviruses in HTLV-1-induced tumors (30, 37, 46). These findings suggest that a signal transduction pathway that controls the activity of Tax in host cells, rather than any genetic change in the BLV proviral genome, might play an important role in regulating the activation and silencing of the virus. In this study, we amplified Tax genes from BLV-infected animals using PCR, and then we cloned and sequenced the genes and identified seven independent Tax mutants, which were associated with strikingly higher viral LTR-directed transcriptional activity than the wild type. Furthermore, we found that amino acid substitutions between amino acids 240 and 265 of Tax resulted in significantly increased transactivational activity that involved a CRE motif in the BLV LTR. Finally, we demonstrated that the mutant Tax Protein also significantly activated the 21-bp enhancer of HTLV-1 and the LTR of mouse mammary tumor virus (MMTV) and was slightly effective with the LTRs of HIV type 1 (HIV-1) and of Moloney murine leukemia virus (M-MLV). The mutant Tax Proteins with elevated transactivation activity might help us to elucidate the mechanism for strict regulation of the expression of BLV.
Louis Gazzolo - One of the best experts on this subject based on the ideXlab platform.
-
Tax Protein of human T-cell leukaemia virus type 1 induces interleukin 17 gene expression in T cells
Journal of General Virology, 2004Co-Authors: Madeleine Duc Dodon, Samir Hamaia, Louis GazzoloAbstract:Tax Protein of human T-cell leukaemia virus type 1 (HTLV-1) induces the expression of several cellular genes that are involved in T cell activation and proliferation. In this study, it was observed that Tax upregulated the expression of human interleukin 17 (IL17), a cytokine mainly produced by activated CD4(+) memory T cells. Indeed, IL17 mRNA was highly expressed in HTLV-1-infected T cells as well as in Tax-expressing Jurkat T cells, whereas it was not detectable in HTLV-1-negative T cell lines. The clinical relevance of these observations was further demonstrated by quantitative assessment of IL17 expression in lymphocytes isolated from one HTLV-1-infected patient. To define the transcriptional activation of the IL17 gene by Tax, the 5'-flanking region of this gene was cloned and a reporter gene analysis performed. The presence of a Tax-responsive region spanning 614 bp upstream of the initiation start site was identified, in HeLa as well as in Jurkat cells, stimulated with phorbol myristate acetate and Ca(2+) ionophore. Finally, Tax mutants were used to show that the transcriptional activation of the IL17 promoter by Tax was dependent on the CREB/ATF pathway. As IL17 upregulates the expression of several pro-inflammatory cytokines, these observations provide new insights into the involvement of the Tax Protein in the pathophysiology of HTLV-1-associated inflammatory disorders.
-
Vascular cell adhesion molecule-1 induced by human T-cell leukaemia virus type 1 Tax Protein in T-cells stimulates proliferation of human T-lymphocytes.
The Journal of general virology, 2001Co-Authors: Hélène Valentin, Samir Hamaia, Stéphane König, Louis GazzoloAbstract:Human T-cell leukaemia/lymphotropic virus type 1 (HTLV-1), aetiologically linked to lymphoproliferative as well as inflammatory diseases, infects and activates CD4(+) helper T-cells and thus alters immunoregulatory pathways. The viral regulatory Tax Protein has been shown previously to induce the expression of vascular cell adhesion molecule-1 (VCAM-1) by T-cells. To determine the functional role of this adhesion molecule, Jurkat T-cells stably expressing either Tax or both Tax and Rex (another viral regulatory Protein) were used in binding and coculture assays performed with either control Jurkat cells or primary human T-lymphocytes. Evidence was provided that VCAM-1 acting in synergy with leucocyte function-associated antigen-3 promotes T-cell-T-cell interactions and increases T-cell proliferation. Interestingly, Rex was found to modulate these events. These data establish that VCAM-1 induced by Tax on T-cells thus contributes to the immunopathological process triggered by HTLV-1 infection.
-
the human t cell leukemia lymphotropic virus type 1 Tax Protein represses myod dependent transcription by inhibiting myod binding to the kix domain of p300 a potential mechanism for Tax mediated repression of the transcriptional activity of basic hel
Journal of Biological Chemistry, 2000Co-Authors: Patrice Riou, Françoise Bex, Louis GazzoloAbstract:The human T cell leukemia/lymphotropic virus type 1 (HTLV-1) Tax Protein strongly activates viral and cellular gene transcription. It mainly functions by interacting with cellular transcription factors and the KIX domain of the p300/CBP coactivators. Tax can also repress the transcription of cellular genes through the basic helix-loop-helix (bHLH) Protein family. To investigate the molecular mechanisms of this Tax-mediated inhibition, we analyzed its effect on the transcriptional activity of the myogenic MyoD Protein, which was used as a paradigm of bHLH factors. In this study, we show that overexpression of the p300 coactivator in transient transfection assays was sufficient to rescue MyoD repression by Tax. Furthermore, an N-terminal domain of p300 (amino acids 379-654) containing the region of KIX serving as the Tax binding site was found, when overexpressed, to potentiate Tax-mediated transactivation of HTLV-1 proviral as well as MyoD-dependent transcription, and to antagonize the inhibition by Tax of the transcriptional activity of MyoD. These results revealing the presence of an N-terminal MyoD binding site were confirmed by in vitro Protein-Protein interaction assays that demonstrate that MyoD binds to the KIX domain of p300 and that Tax competes with MyoD binding in a nonreciprocal manner. These observations provide evidence that Tax binding to the KIX domain of p300 prevents bHLH Proteins from contacting this N-terminal domain of the coactivator, thus resulting in their transcriptional repression. As bHLH Proteins are implicated in many developmental fate decisions, especially during thymopoiesis, Tax-mediated inhibition of their transcriptional activity may contribute to the induction of HTLV-1-linked leukemogenesis.
-
Identification of a negative element in the human vimentin promoter: modulation by the human T-cell leukemia virus type I Tax Protein.
Molecular and cellular biology, 1993Co-Authors: Anna Salvetti, Alain Lilienbaum, Denise Paulin, Louis GazzoloAbstract:The vimentin gene is a member of the intermediate filament multigene family and encodes a Protein expressed, in vivo, in all mesenchymal derivatives and, in vitro, in cell types of various origin. We have previously demonstrated that the expression of this growth-regulated gene could be trans activated by the 40-kDa Tax Protein of HTLV-I (human T-cell leukemia virus type I) and that responsiveness to this viral Protein was mediated by the presence of an NF-kappa B binding site located between -241 and -210 bp upstream of the mRNA cap site (A. Lilienbaum, M. Duc Dodon, C. Alexandre, L. Gazzolo, and D. Paulin, J. Virol. 64:256-263, 1990). These previous assays, performed with deletion mutants of the vimentin promoter linked to the chloramphenicol acetyltransferase gene, also revealed the presence of an upstream negative region between -529 and -241 bp. Interestingly, the inhibitory activity exerted by this negative region was overcome after cotransfection of a Tax-expressing plasmid. In this study, we further characterize the vimentin negative element and define the effect of the Tax Protein on the inhibitory activity of this element. We first demonstrate that a 187-bp domain (-424 to -237 bp) behaves as a negative region when placed upstream either of the NF-kappa B binding site of vimentin or of a heterologous enhancer such as that present in the desmin gene promoter. The negative effect can be further assigned to a 32-bp element which is indeed shown to repress the basal or induced activity of the NF-kappa B binding site.(ABSTRACT TRUNCATED AT 250 WORDS)
-
Organization and expression of intermediate filaments in epithelial cells expressing the HTLV-I Tax Protein.
European journal of cell biology, 1993Co-Authors: Anna Salvetti, Denise Paulin, A. Lilienbaum, Marie-madeleine Portier, Pierre Gounon, Louis GazzoloAbstract:Intermediate filaments (IF) represent major components of the cytoskeletal network. These Proteins which are differentially expressed according to the cell type, constitute a dynamic structure which not only contributes to the cell architecture but also defines its state of differentiation. Furthermore, numerous observations have shown that the IF network is altered in cells transformed by tumorigenic viruses. We have previously demonstrated that HTLV-I (human T-cell leukemia virus type I) transformed T cells were characterized by a high level of vimentin transcripts and that the HTLV-I Tax regulatory Protein was able to transactivate the vimentin promoter transfected into Jurkat and HeLa cells. To enlarge the scope of this study, we investigated the effects of the Tax Protein on the expression and organization of IF of epithelial cells in which the IF network is composed of vimentin and cytokeratin. To this aim, we have developed a model of epithelial cells (HeLa) stably expressing the Tax sequences which were introduced by using retrovirus-mediated gene transfer. Half of the Tax expressing HeLa clones were loosely adherent to the culture surface and were displaying remarkable morphological alterations, as ascertained by the presence of round-shaped or spindle-shaped cells. In these cells, expression of this viral Protein correlated to a pronounced disruption in the distribution of both the vimentin and the cytokeratin networks, as shown by immunofluorescence and ultrastructural analysis. Indeed, vimentin filaments appeared to be concentrated in discrete spots throughout the cytoplasm, while the cytokeratin filaments appeared to form a dense ring around the nucleus. More importantly, mRNA and Protein analysis indicate an enhanced expression of the cytokeratin 7 gene.(ABSTRACT TRUNCATED AT 250 WORDS)
