scholarly journals Splicing factor SRSF1 limits IFN-γ production via RhoH and ameliorates experimental nephritis

Rheumatology ◽  
2020 ◽  
Vol 60 (1) ◽  
pp. 420-429
Author(s):  
Takayuki Katsuyama ◽  
Hao Li ◽  
Suzanne M Krishfield ◽  
Vasileios C Kyttaris ◽  
Vaishali R Moulton
Keyword(s):  
T Cells ◽  
T Cell ◽  
Molecular Mechanisms ◽  
Elevated Serum ◽  
Splicing Factor ◽  
Type I ◽  
Human T Cells ◽  
Experimental Nephritis ◽  
Ifn Γ

Abstract Objective CD4 T helper 1 (Th1) cells producing IFN-γ contribute to inflammatory responses in the pathogenesis of SLE and lupus nephritis. Moreover, elevated serum type II IFN levels precede the appearance of type I IFNs and autoantibodies in patient years before clinical diagnosis. However, the molecules and mechanisms that control this inflammatory response in SLE remain unclear. Serine/arginine-rich splicing factor 1 (SRSF1) is decreased in T cells from SLE patients, and restrains T cell hyperactivity and systemic autoimmunity. Our objective here was to evaluate the role of SRSF1 in IFN-γ production, Th1 differentiation and experimental nephritis. Methods T cell-conditional Srsf1-knockout mice were used to study nephrotoxic serum-induced nephritis and evaluate IFN-γ production and Th1 differentiation by flow cytometry. RNA sequencing was used to assess transcriptomics profiles. RhoH was silenced by siRNA transfections in human T cells by electroporation. RhoH and SRSF1 protein levels were assessed by immunoblots. Results Deletion of Srsf1 in T cells led to increased Th1 differentiation and exacerbated nephrotoxic serum nephritis. The expression levels of RhoH are decreased in Srsf1-deficient T cells, and silencing RhoH in human T cells leads to increased production of IFN-γ. Furthermore, RhoH expression was decreased and directly correlated with SRSF1 in T cells from SLE patients. Conclusion Our study uncovers a previously unrecognized role of SRSF1 in restraining IFN-γ production and Th1 differentiation through the control of RhoH. Reduced expression of SRSF1 may contribute to pathogenesis of autoimmune-related nephritis through these molecular mechanisms.

scholarly journals Type I Interferons Are Essential in Controlling Neurotropic Coronavirus Infection Irrespective of Functional CD8 T Cells

2007 ◽  
Vol 82 (1) ◽  
pp. 300-310 ◽  
Author(s):  
Derek D. C. Ireland ◽  
Stephen A. Stohlman ◽  
David R. Hinton ◽  
Roscoe Atkinson ◽  
Cornelia C. Bergmann
Keyword(s):  
T Cells ◽  
T Cell ◽  
Viral Replication ◽  
Cd8 T Cells ◽  
Cd8 T Cell ◽  
Type I ◽  
Virus Variant ◽  
Coronavirus Infection ◽  
Ifn Γ

ABSTRACT Neurotropic coronavirus infection induces expression of both beta interferon (IFN-β) RNA and protein in the infected rodent central nervous system (CNS). However, the relative contributions of type I IFN (IFN-I) to direct, cell-type-specific virus control or CD8 T-cell-mediated effectors in the CNS are unclear. IFN-I receptor-deficient (IFNAR−/−) mice infected with a sublethal and demyelinating neurotropic virus variant and those infected with a nonpathogenic neurotropic virus variant both succumbed to infection within 9 days. Compared to wild-type (wt) mice, replication was prominently increased in all glial cell types and spread to neurons, demonstrating expanded cell tropism. Furthermore, increased pathogenesis was associated with significantly enhanced accumulation of neutrophils, tumor necrosis factor alpha, interleukin-6, chemokine (C-C motif) ligand 2, and IFN-γ within the CNS. The absence of IFN-I signaling did not impair induction or recruitment of virus-specific CD8 T cells, the primary adaptive mediators of virus clearance in wt mice. Despite similar IFN-γ-mediated major histocompatibility complex class II upregulation on microglia in infected IFNAR−/− mice, class I expression was reduced compared to that on microglia in wt mice, suggesting a synergistic role of IFN-I and IFN-γ in optimizing class I antigen presentation. These data demonstrate a critical direct antiviral role of IFN-I in controlling virus dissemination within the CNS, even in the presence of potent cellular immune responses. By limiting early viral replication and tropism, IFN-I controls the balance of viral replication and immune control in favor of CD8 T-cell-mediated protective functions.

scholarly journals Safety Profile of a Virus-Like Particle-Based Vaccine Targeting Self-Protein Interleukin-5 in Horses

Vaccines ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 213 ◽  
Author(s):  
Sigridur Jonsdottir ◽  
Victoria Fettelschoss ◽  
Florian Olomski ◽  
Stephanie C. Talker ◽  
Jelena Mirkovitch ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cell ◽  
Mononuclear Cells ◽  
Clinical Signs ◽  
T Cell Response ◽  
Type I ◽  
Cell Responses ◽  
Virus Like Particle ◽  
Ifn Γ

Background: Insect bite hypersensitivity (IBH) is an eosinophilic allergic dermatitis of horses caused by type I/IVb reactions against mainly Culicoides bites. The vaccination of IBH-affected horses with equine IL-5 coupled to the Cucumber mosaic virus-like particle (eIL-5-CuMVTT) induces IL-5-specific auto-antibodies, resulting in a significant reduction in eosinophil levels in blood and clinical signs. Objective: the preclinical and clinical safety of the eIL-5-CuMVTT vaccine. Methods: The B cell responses were assessed by longitudinal measurement of IL-5- and CuMVTT-specific IgG in the serum and plasma of vaccinated and unvaccinated horses. Further, peripheral blood mononuclear cells (PBMCs) from the same horses were re-stimulated in vitro for the proliferation and IFN-γ production of specific T cells. In addition, we evaluated longitudinal kidney and liver parameters and the general blood status. An endogenous protein challenge was performed in murine IL-5-vaccinated mice. Results: The vaccine was well tolerated as assessed by serum and cellular biomarkers and also induced reversible and neutralizing antibody titers in horses and mice. Endogenous IL-5 stimulation was unable to re-induce anti-IL-5 production. The CD4+ T cells of vaccinated horses produced significantly more IFN-γ and showed a stronger proliferation following stimulation with CuMVTT as compared to the unvaccinated controls. Re-stimulation using E. coli-derived proteins induced low levels of IFNγ+CD4+ cells in vaccinated horses; however, no IFN-γ and proliferation were induced following the HEK-eIL-5 re-stimulation. Conclusions: Vaccination using eIL-5-CuMVTT induces a strong B-cell as well as CuMVTT-specific T cell response without the induction of IL-5-specific T cell responses. Hence, B-cell unresponsiveness against self-IL-5 can be bypassed by inducing CuMVTT carrier-specific T cells, making the vaccine a safe therapeutic option for IBH-affected horses.

Constitutive Activation of Toll like Receptor Signaling in Adult T-Cell Leukemia Cells.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2291-2291
Author(s):  
Takamitsu Mizobe ◽  
Junichi Tsukada ◽  
Takehiro Higashi ◽  
Fumihiko Mouri ◽  
Ai Matsuura ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Adaptor Protein ◽  
T Cell Leukemia ◽  
Cell Leukemia ◽  
Constitutive Activation ◽  
Adult T Cell Leukemia ◽  
Human T Cells

Abstract Human T-cell leukemia virus type I (HTLV-I) is etiologically associated with the development of an aggressive and fatal malignancy of CD4+ T lymphocytes called adult T-cell leukemia (ATL). Constitutive activation of nuclear factor-κB (NF-κB) is a common feature of ATL. Although the mechanism by which NF-κB is spontaneously activated in ATL cells still remains unclear, inhibition of NF-κB activity induces apoptosis, suggesting a central role of NF-κB in their proliferation. Toll like receptors (TLRs) are involved in innate cell activation by conserved structures expressed by microorganisms. Engagement of IL-1R or TLR with their cognate ligands causes an adaptor protein MyD88 to be recruited to the receptor complex, which in turn promotes its association with the IL-1R-associated kinase (IRAK) via an interaction between the respective death domains of each molecule. Several recent reports have indicated unique expression profiles of TLRs on different subsets of human T cells, and that some TLR ligands modulate the function of human T cells. We examined expression of the TLR mRNAs in primary ATL cells and ATL cell lines, MT2, MT4 and HUT102 by RT-PCR. Expression of TLR mRNAs, except of TLR7 and TLR8, was detected in all cell samples examined. We further demonstrated constitutive association of MyD88, an adaptor protein for the TLR signaling, with the IL-1R-associated kinase 1 (IRAK1) in ATL cell lines, MT2, MT4 and HUT102. In MT2 cells, constitutive activation of NF-κB and NF-IL6, but not Stat3 was significantly inhibited by expression of a dominant negative form of MyD88 protein (MyD88dn). Spontaneous transcriptional activation of IL-1α, IFN-γ and TNF-α gene promoters in MT2 cells was also suppressed by MyD88dn expression. MyD88dn inhibited cell proliferation and induced apoptosis of MT2 cells. In addition, overexpression of wild-type MyD88 and HTLV-I Tax induces synergistically transcriptional activity of NF-κB in 293T cells, showing interaction of Tax with MyD88. Thus, our results show a critical role of MyD88 in dysregulated gene activation and cell proliferation in HTLV-I-transformed T-cells, and further suggest the involvement of MyD88 in Tax-mediated intracellular signal transduction in HTLV-I-infected cells. Considering the fact that blocking NF-κB is a potential strategy to treat ATL, our argument raises a possibility that we may be able to find new treatment targets against ATL.

CD11b+gr-1+ myeloid Derived Suppressor Cells (MDSC) In Normal Bone Marrow Suppress T Cell Proliferation and Enhance T-Regulatory Function Via a IL10-, IL4- and IDO-Independent Mechanism

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4801-4801 ◽  
Author(s):  
Parvin Forghani ◽  
Wayne Harris ◽  
jian-Ming Li ◽  
M.R. Khorramizadeh ◽  
Edmund Waller
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Regulatory Function ◽  
T Cell Proliferation ◽  
Suppressive Activity ◽  
Ifn Γ

Abstract Abstract 4801 MDSC have been described as an important negative regulators of autologous anti-cancer immune responses. Considering the important role of MDSC in immune regulation in allogenic stem cell and organ transplantation, we undertook an investigation of the mechanism(s) by which MDSC inhibit T–cell activation and proliferation, and tested the hypothesis that local cytokine secretion or IDO activity is required for suppression of T-cell proliferation. Two separate populations CD11bhiGr-1hi and CD11bhi Gr-1int were isolated by high-speed FACS from lineage- BM antigen presenting cells (C57 & BALB/c mice). Both MDSC subsets had potent capacity for in–vitro suppression of CD4+ and CD8+ T cells proliferation in response to anti-CD3/anti-CD28 beads and Con A. A ratio of 0.5/1 MDSC: T-cells were sufficient to inhibit >66% control levels of T-cell proliferation. MDSC isolated from transgenic mice that had been “knocked-out” for IFN-γ and IDO had equivalent suppressive activity as MDSC from wild-type donors. Addition of saturating concentrations of anti IL-10 and IL-4 MAb, or in combination with anti- IFN-γ MAb did not abrogate MDSC-suppressive activity. Ex-vivo culture of MDSC with mitogen-activated T-cells generated two—fold more Fox-p3 T-reg compared with cultures of T cell plus mitogen. Data will be presented regarding the novel role of MDSC involving in the homeostasis regulation of normal T-cell activation and proliferation in non-tumor-bearing mice. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Effector CD8+ T Lymphocytes against Liver Stages of Plasmodium yoelii Do Not Require Gamma Interferon for Antiparasite Activity

2008 ◽  
Vol 76 (8) ◽  
pp. 3628-3631 ◽  
Author(s):  
Sumana Chakravarty ◽  
G. Christian Baldeviano ◽  
Michael G. Overstreet ◽  
Fidel Zavala
Keyword(s):  
T Cells ◽  
T Cell ◽  
Protective Immunity ◽  
Critical Role ◽  
Plasmodium Yoelii ◽  
Gamma Interferon ◽  
Parasite Development ◽  
Wild Type ◽  
Ifn Γ

ABSTRACT The protective immune response against liver stages of the malaria parasite critically requires CD8+ T cells. Although the nature of the effector mechanism utilized by these cells to repress parasite development remains unclear, a critical role for gamma interferon (IFN-γ) has been widely assumed based on circumstantial evidence. However, the requirement for CD8+ T-cell-mediated IFN-γ production in protective immunity to this pathogen has not been directly tested. In this report, we use an adoptive transfer strategy with circumsporozoite (CS) protein-specific transgenic T cells to examine the role of CD8+ T-cell-derived IFN-γ production in Plasmodium yoelii-infected mice. We show that despite a marginal reduction in the expansion of naive IFN-γ-deficient CS-specific transgenic T cells, their antiparasite activity remains intact. Further, adoptively transferred IFN-γ-deficient CD8+ T cells were as efficient as their wild-type counterparts in limiting parasite growth in naive mice. Taken together, these studies demonstrate that IFN-γ secretion by CS-specific CD8+ T cells is not essential to protect mice against live sporozoite challenge.

scholarly journals Role of Type I Interferon Signaling in Human Metapneumovirus Pathogenesis and Control of Viral Replication

2015 ◽  
Vol 89 (8) ◽  
pp. 4405-4420 ◽  
Author(s):  
Andrew K. Hastings ◽  
John J. Erickson ◽  
Jennifer E. Schuster ◽  
Kelli L. Boyd ◽  
Sharon J. Tollefson ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Human Metapneumovirus ◽  
Type I ◽  
Type I Ifn ◽  
Inhibitory Receptor ◽  
Programmed Death ◽  
Hmpv Infection ◽  
Antigen Presenting

ABSTRACTType I IFN signaling, which is initiated through activation of the alpha interferon receptor (IFNAR), regulates the expression of proteins that are crucial contributors to immune responses. Paramyxoviruses, including human metapneumovirus (HMPV), have evolved mechanisms to inhibit IFNAR signaling, but the specific contribution of IFNAR signaling to the control of HMPV replication, pathogenesis, and adaptive immunity is unknown. We used IFNAR-deficient (IFNAR−/−) mice to assess the effect of IFNAR signaling on HMPV replication and the CD8+T cell response. HMPV-infected IFNAR−/−mice had a higher peak of early viral replication but cleared the virus with kinetics similar to those of wild-type (WT) mice. However, IFNAR−/−mice infected with HMPV displayed less airway dysfunction and lung inflammation. CD8+T cells of IFNAR−/−mice after HMPV infection expressed levels of the inhibitory receptor programmed death 1 (PD-1) similar to those of WT mice. However, despite lower expression of inhibitory programmed death ligand 1 (PD-L1), HMPV-specific CD8+T cells of IFNAR−/−mice were more functionally impaired than those of WT mice and upregulated the inhibitory receptor Tim-3. Analysis of the antigen-presenting cell subsets in the lungs revealed that the expansion of PD-L1lowdendritic cells (DCs), but not PD-L1highalveolar macrophages, was dependent on IFNAR signaling. Collectively, our results indicate a role for IFNAR signaling in the early control of HMPV replication, disease progression, and the development of an optimal adaptive immune response. Moreover, our findings suggest an IFNAR-independent mechanism of lung CD8+T cell impairment.IMPORTANCEHuman metapneumovirus (HMPV) is a leading cause of acute respiratory illness. CD8+T cells are critical for clearing viral infection, yet recent evidence shows that HMPV and other respiratory viruses induce CD8+T cell impairment via PD-1–PD-L1 signaling. We sought to understand the role of type I interferon (IFN) in the innate and adaptive immune responses to HMPV by using a mouse model lacking IFN signaling. Although HMPV titers were higher in the absence of type I IFN, virus was nonetheless cleared and mice were less ill, indicating that type I IFN is not required to resolve HMPV infection but contributes to pathogenesis. Further, despite lower levels of the inhibitory ligand PD-L1 in mice lacking type I IFN, CD8+T cells were more impaired in these mice than in WT mice. Our data suggest that specific antigen-presenting cell subsets and the inhibitory receptor Tim-3 may contribute to CD8+T cell impairment.

scholarly journals Retrovirally induced CTL degranulation mediated by IL-15 expression and infection of mononuclear phagocytes in patients with HTLV-I–associated neurologic disease

Blood ◽  
2008 ◽  
Vol 112 (6) ◽  
pp. 2400-2410 ◽  
Author(s):  
Yoshimi Enose-Akahata ◽  
Unsong Oh ◽  
Christian Grant ◽  
Steven Jacobson
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cd8 T Cells ◽  
Cd4 T Cells ◽  
Spastic Paraparesis ◽  
Cd8 T Cell ◽  
Mononuclear Phagocytes ◽  
Type I ◽  
Human T Cell ◽  
Ifn Γ

AbstractCD8+ T cells contribute to central nervous system inflammation in human T-cell lymphotropic virus type I (HTLV-I)–associated myelopathy/tropical spastic paraparesis (HAM/TSP). We analyzed CD8+ T-cell dysfunction (degranulation and IFN-γ production) and have demonstrated that CD8+ T cells of patients with HAM/TSP (HAM/TSP patients) spontaneously degranulate and express IFN-γ in ex vivo unstimulated culture. CD8+ T cells of HTLV-I asymptomatic carriers and healthy donors did not. Spontaneous degranulation was detected in Tax11-19/HLA-A*201 tetramer+ cells, but not in CMV pp65 tetramer+ cells. Interestingly, degranulation and IFN-γ production in CD8+ T cells was induced by coculture with autologous CD14+ cells, but not CD4+ T cells, of HAM/TSP patients, which correlated with proviral DNA load in CD14+ cells of infected patients. Moreover, the expression of IL-15, which induced degranulation and IFN-γ production in infected patients, was enhanced on surface of CD14+ cells in HAM/TSP patients. Blockade of MHC class I and IL-15 confirmed these results. Thus, CD8+ T-cell dysregulation was mediated by both virus infection and enhanced IL-15 on CD14+ cells in HAM/TSP patients. Despite lower viral expression than in CD4+ T cells, HTLV-I–infected or –activated CD14+ cells may be a heretofore important but under recognized reservoir particularly in HAM/TSP patients.

scholarly journals Dysregulated T cell expression of TIM3 in multiple sclerosis

2006 ◽  
Vol 203 (6) ◽  
pp. 1413-1418 ◽  
Author(s):  
Ken Koguchi ◽  
David E. Anderson ◽  
Li Yang ◽  
Kevin C. O'Connor ◽  
Vijay K. Kuchroo ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
T Cells ◽  
T Cell ◽  
Ex Vivo ◽  
Interleukin 12 ◽  
Intrinsic Defect ◽  
Control Subjects ◽  
Human T Cells ◽  
Ifn Γ ◽  
Cell Expression

T cell immunoglobulin- and mucin domain–containing molecule (TIM)3 is a T helper cell (Th)1–associated cell surface molecule that regulates Th1 responses and promotes tolerance in mice, but its expression and function in human T cells is unknown. We generated 104 T cell clones from the cerebrospinal fluid (CSF) of six patients with multiple sclerosis (MS) (n = 72) and four control subjects (n = 32) and assessed their cytokine profiles and expression levels of TIM3 and related molecules. MS CSF clones secreted higher amounts of interferon (IFN)-γ than did those from control subjects, but paradoxically expressed lower levels of TIM3 and T-bet. Interleukin 12–mediated polarization of CSF clones induced substantially higher amounts of IFN-γ secretion but lower levels of TIM3 in MS clones relative to control clones, demonstrating that TIM3 expression is dysregulated in MS CSF clones. Reduced levels of TIM3 on MS CSF clones correlated with resistance to tolerance induced by costimulatory blockade. Finally, reduction of TIM3 on ex vivo CD4+ T cells using small interfering (si)RNA enhanced proliferation and IFN-γ secretion, directly demonstrating that TIM3 expression on human T cells regulates proliferation and IFN-γ secretion. Failure to up-regulate T cell expression of TIM3 in inflammatory sites may represent a novel, intrinsic defect that contributes to the pathogenesis of MS and other human autoimmune diseases.

scholarly journals Organ- and Disease-Stage-Specific Regulation of Toxoplasma gondii-Specific CD8-T-Cell Responses by CD4 T Cells

2006 ◽  
Vol 74 (10) ◽  
pp. 5790-5801 ◽  
Author(s):  
Sonja Lütjen ◽  
Sabine Soltek ◽  
Simona Virna ◽  
Martina Deckert ◽  
Dirk Schlüter
Keyword(s):  
T Cells ◽  
T Cell ◽  
Toxoplasma Gondii ◽  
Cd8 T Cells ◽  
Functional Activity ◽  
Cd4 T Cells ◽  
Cd8 T Cell ◽  
Cd4 T Cell ◽  
Ifn Γ

ABSTRACT Toxoplasma gondii induces a persistent central nervous system infection, which may be lethally reactivated in AIDS patients with low CD4 T-cell numbers. To analyze the role of CD4 T cells for the regulation of parasite-specific CD8 T cells, mice were infected with transgenic T. gondii expressing the CD8 T-cell antigen β-galactosidase (β-Gal). Depletion of CD4 T cells prior to infection did not affect frequencies of β-Gal876-884-specific (consisting of residues 876 to 884 of β-Gal) CD8 T cells but resulted in a pronounced reduction of intracerebral β-Gal-specific gamma interferon (IFN-γ)-producing and cytolytic CD8 T cells. After cessation of anti-CD4 treatment a normal T. gondii-specific CD4 T-cell response developed, but IFN-γ production of intracerebral β-Gal-specific CD8 T cells remained impaired. The important supportive role of CD4 T cells for the optimal functional activity of intracerebral CD8 T cells was also observed in mice that had been depleted of CD4 T cells during chronic toxoplasmosis. Reinfection of chronically infected mice that had been depleted of CD4 T cells during either the acute or chronic stage of infection resulted in an enhanced proliferation of β-Gal-specific IFN-γ-producing splenic CD8 T cells. However, reinfection of chronically infected mice that had been depleted of CD4 T cells in the acute stage of infection did not reverse the impaired IFN-γ production of intracerebral CD8 T cells. Collectively, these findings illustrate that CD4 T cells are not required for the induction and maintenance of parasite-specific CD8 T cells but, depending on the stage of infection, the infected organ and parasite challenge infection regulate the functional activity of intracerebral CD8 T cells.

scholarly journals p53 functional impairment and high p21waf1/cip1 expression in human T- cell lymphotropic/leukemia virus type I-transformed T cells

Blood ◽  
1996 ◽  
Vol 88 (5) ◽  
pp. 1551-1560 ◽  
Author(s):  
A Cereseto ◽  
F Diella ◽  
JC Mulloy ◽  
A Cara ◽  
P Michieli ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Virus Type ◽  
Cell Transformation ◽  
Leukemia Virus ◽  
Type I ◽  
Wild Type ◽  
Human T Cell ◽  
Wild Type P53

Abstract Human T-cell lymphotropic/leukemia virus type I (HTLV-I) is associated with T-cell transformation both in vivo and in vitro. Although some of the mechanisms responsible for transformation remain unknown, increasing evidence supports a direct role of viral as well as dysregulated cellular proteins in transformation. We investigated the potential role of the tumor suppressor gene p53 and of the p53- regulated gene, p21waf1/cip1 (wild-type p53 activated fragment 1/cycling dependent kinases [cdks] interacting protein 1), in HTLV-I- infected T cells. We have found that the majority of HTLV-I-infected T cells have the wild-type p53 gene. However, its function in HTLV-I- transformed cells appears to be impaired, as shown by the lack of appropriate p53-mediated responses to ionizing radiation (IR). Interestingly, the expression of the p53 inducible gene, p21waf1/cip1, is elevated at the messenger ribonucleic acid and protein levels in all HTLV-I-infected T-cell lines examined as well as in Taxl-1, a human T- cell line stably expressing Tax. Additionally, Tax induces upregulation of a p21waf1/cip1 promoter-driven luciferase gene in p53 null cells, and increases p21waf1/cip1 expression in Jurkat T cells. These findings suggest that the Tax protein is at least partially responsible for the p53-independent expression of p21waf1/cip1 in HTLV-I-infected cells. Dysregulation of p53 and p21waf1/cip1 proteins regulating cell-cycle progression, may represent an important step in HTLV-I-induced T-cell transformation.

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