Human T-cell leukemia virus type 1 Tax protein induces the expression of STAT1 and STAT5 genes in T-cells

Trans-Activation of the Coactivator-Associated Arginine Methyltransferase 1 (Carm1) Gene by the Oncogene Product Tax of Human T-Cell Leukemia Virus Type 1

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma. The oncogene product Tax of HTLV-I is thought to play crucial roles in leukemogenesis by promoting proliferation of the virus-infected cells through activation of growth-promoting genes. These genes code for growth factors and their receptors, cytokines, cell adhesion molecules, growth signal transducers, transcription factors and cell cycle regulators. We show here that Tax activates the gene coding for coactivator-associated arginine methyltransferase 1 (CARM1), which epigenetically enhances gene expression through methylation of histones. Tax activated the Carm1 gene and increased protein expression, not only in human T-cell lines but also in normal peripheral blood lymphocytes (PHA-PBLs). Tax increased R17-methylated histone H3 on the target gene IL-2Rα, concomitant with increased expression of CARM1. Short hairpin RNA (shRNA)-mediated knockdown of CARM1 decreased Tax-mediated induction of IL-2Rα and Cyclin D2 gene expression, reduced E2F activation and inhibited cell cycle progression. Tax acted via response elements in intron 1 of the Carm1 gene, through the NF-κB pathway. These results suggest that Tax-mediated activation of the Carm1 gene contributes to leukemogenic target-gene expression and cell cycle progression, identifying the first epigenetic target gene for Tax-mediated trans-activation in cell growth promotion.

The HTLV-1 viral oncoproteins Tax and HBZ reprogram the cellular mRNA splicing landscape

Viral infections are known to hijack the transcription and translation of the host cell. However, the extent to which viral proteins coordinate these perturbations remains unclear. Here we used a model system, the human T-cell leukemia virus type 1 (HTLV-1), and systematically analyzed the transcriptome and interactome of key effectors oncoviral proteins Tax and HBZ. We showed that Tax and HBZ target distinct but also common transcription factors. Unexpectedly, we also uncovered a large set of interactions with RNA-binding proteins, including the U2 auxiliary factor large subunit (U2AF2), a key cellular regulator of pre-mRNA splicing. We discovered that Tax and HBZ perturb the splicing landscape by altering cassette exons in opposing manners, with Tax inducing exon inclusion while HBZ induces exon exclusion. Among Tax- and HBZ-dependent splicing changes, we identify events that are also altered in Adult T cell leukemia/lymphoma (ATLL) samples from two independent patient cohorts, and in well-known cancer census genes. Our interactome mapping approach, applicable to other viral oncogenes, has identified spliceosome perturbation as a novel mechanism coordinated by Tax and HBZ to reprogram the transcriptome.

Tax and HBZ are two viral regulatory proteins encoded by the human T-cell leukemia virus type 1 (HTLV-1) via sense and antisense transcripts, respectively. Both proteins are known to drive oncogenic processes that culminate in a T-cell neoplasm, known as Adult T cell leukemia/lymphoma (ATLL). We measured the effects of Tax and HBZ on host gene expression pathway by analyzing the interactome with cellular transcriptional and post-transcriptional regulators, and the transcriptome and mRNA splicing of cell lines expressing either Tax or HBZ. We compared our results with data obtained from independent cohorts of Japanese and Afro-Caribbean patients, and identified common splicing changes that might represent clinically useful biomarkers for ATLL. Finally, we provide evidence that the viral protein Tax can reprogram initial steps of the T-cell transcriptome diversification by hijacking the U2AF complex, a key cellular regulator of pre-mRNA splicing.

The Dynamic Interface of Viruses with STATs

Viruses commonly antagonize the antiviral type I interferon response by targeting signal transducer and activator of transcription 1 (STAT1) and STAT2, key mediators of interferon signaling. Other STAT family members mediate signaling by diverse cytokines important to infection, but their relationship with viruses is more complex. Importantly, virus-STAT interaction can be antagonistic or stimulatory depending on diverse viral and cellular factors. While STAT antagonism can suppress immune pathways, many viruses promote activation of specific STATs to support viral gene expression and/or produce cellular conditions conducive to infection. It is also becoming increasingly clear that viruses can hijack noncanonical STAT functions to benefit infection. For a number of viruses, STAT function is dynamically modulated through infection as requirements for replication change. Given the critical role of STATs in infection by diverse viruses, the virus-STAT interface is an attractive target for the development of antivirals and live-attenuated viral vaccines. Here, we review current understanding of the complex and dynamic virus-STAT interface and discuss how this relationship might be harnessed for medical applications.

A Central Role for STAT3 in Gammaherpesvirus-Life Cycle and -Diseases

Having co-evolved with humans, herpesviruses have adapted to exploit the host molecular machinery to ensure viral persistence. The cellular protein Signal Transducer and Activator of Transcription 3 (STAT3) is a leading example. STAT3 is a prominent transcription factor that functions in a variety of physiologic processes including embryonic development, inflammation, immunity, and wound healing. Generally activated via growth factor and cytokine signaling, STAT3 can transcriptionally drive oncoproteins, pro-survival and pro-proliferative proteins as well as angiogenic factors, thereby contributing to cancer. As in most non-viral cancers, STAT3 is constitutively active in EBV-related B and epithelial cell cancers and in animal models of KSHV-cancers. Again, similar to non-viral cancers, STAT3 contributes to gammaherpesvirus (EBV and KSHV)-mediated cancers by driving cell proliferation, invasion and angiogenesis. Being herpesviruses, EBV and KSHV establish latency in humans with episodic lytic activation. Importantly, both viruses activate STAT3 almost immediately upon infection of primary cells. In the setting of infection of primary B cells by EBV, this rapidly activated STAT3 plays a key role in suppressing the DNA damage response (DDR) to EBV-oncogene triggered replication stress, thereby facilitating B cell proliferation and ultimately establishment of latency. STAT3 also contributes to maintenance of latency by curbing lytic activation of EBV and KSHV in latent cells that express high levels of STAT3. In this way, gammaherpesviruses exploit STAT3 to overcome cellular anti-proliferative and anti-lytic barriers to promote viral persistence. These investigations into gammaherpesviruses and STAT3 have simultaneously revealed a novel function for STAT3 in suppression of the DDR, a process fundamental to physiologic cell proliferation as well as development of cancer.

Prognostic significance of signal transducer and activator of transcription 5 and 5b expression in Epstein-Barr virus-positive patients with chronic lymphocytic leukemia

Signal transducer and activator of transcription (STAT) proteins have been intensively studied in hematologic malignancies, and the efficacy of agents against STATs in lymphomas is already under research. We investigated the expression of total STAT5 and STAT5b in peripheral blood samples of patients with chronic lymphocytic leukemia (CLL) in correlation with the presence of Epstein-Barr Virus (EBV) and its major oncoprotein (latent membrane protein 1, LMP1). The EBV load was measured in the peripheral blood by real-time PCR for the BXLF1 gene and the levels of LMP1 by PCR and ELISA. Western blotting was performed for total STAT5 and STAT5b in protein extracts. STAT5b was only expressed in patients (not in healthy subjects) and STAT5 but particularly STAT5b expression was correlated with the presence of the virus (77.3% vs. 51.2%, P = 0.006 for STAT5b) and to the expression of LMP1 (58.3% vs. 21.6%, P = 0.011 for STAT5b). Moreover, the expression of STAT5b and the presence of EBV and LMP1 were strongly negatively correlated with the overall survival of the patients (log-rank test P = 0.011, 0.015, 0.006, respectively). Double positive (for EBV and STAT5b) patients had the lowest overall survival (log-rank test P = 0.013). This is the first report of a survival disadvantage of EBV+ patients with CLL, and the first time that STAT5b expression is correlated with survival. The correlation of STAT5 expression with the presence of the virus, along with our survival correlations defines a subgroup of patients with CLL that may benefit from anti-STAT agents.

Regulation of the tumor marker Fascin by the viral oncoprotein Tax of human T-cell leukemia virus type 1 (HTLV-1) depends on promoter activation and on a promoter-independent mechanism

Adult T-cell leukemia/lymphoma is a highly infiltrative neoplasia of CD4(+) T-lymphocytes that occurs in about 5% of carriers infected with the deltaretrovirus human T-cell leukemia virus type 1 (HTLV-1). The viral oncoprotein Tax perturbs cellular signaling pathways leading to upregulation of host cell factors, amongst them the actin-bundling protein Fascin, an invasion marker of several types of cancer. However, transcriptional regulation of Fascin by Tax is poorly understood. In this study, we identified a triple mode of transcriptional induction of Fascin by Tax, which requires (1) NF-κB-dependent promoter activation, (2) a Tax-responsive region in the Fascin promoter, and (3) a promoter-independent mechanism sensitive to the Src family kinase inhibitor PP2. Thus, Tax regulates Fascin by a multitude of signals. Beyond, using Tax-expressing and virus-transformed lymphocytes as a model system, our study is the first to identify the invasion marker Fascin as a novel target of PP2, an inhibitor of metastasis.

HTLV-1-associated adult T cell leukemia is highly susceptible to Navitoclax due to enhanced Bax expression

Over-expression of Bcl-2, Bcl-xL and Bcl-w is frequently associated with cancer resistance to chemotherapy. Navitoclax (ABT-263), an orally bio-available small-molecule mimetic of the Bcl-2 homology domain 3, specifically inhibits Bcl-2, Bcl-xL and Bcl-w. Despite promising results obtained from the clinical trials, the use of Navitoclax in patients is dose-limited due to induction of death of platelets via inhibition of Bcl-xL and subsequent thrombocytopenia. This side effect limits the use of Navitoclax in low doses and to very sensitive tumors. In this study, we show that HTLV-1-associated adult T-cell leukemia/lymphoma (ATL) cells, which over-express Bcl-2, Bcl-xL and Bcl-w, show a 10- to 20-fold higher sensitivity (EC50 = ∼ 25-50 nM) to Navitoclax compared to non-HTLV-1-associated leukemic cells (EC50 = ∼ 1 μM). Investigation of the molecular mechanisms revealed that the HTLV-1 oncogenic protein Tax up-regulates expression of the pro-apoptotic protein Bax which enhances the therapeutic efficacy of Navitoclax. In addition, we show that agents that inhibit the transcription elongation or translation initiation such as Wogonin and Roc-A can further decrease the effective dose of Navitoclax. Our study suggests that HTLV-1 ATL may be a good candidate disease for low dose Navitoclax therapy and probably with less risk of thrombocytopenia.

TCF1 and LEF1 act as T-cell intrinsic HTLV-1 antagonists by targeting Tax

Human T-cell leukemia virus type 1 (HTLV-1) is a delta-type retrovirus that induces malignant and inflammatory diseases during its long persistence in vivo. HTLV-1 can infect various kinds of cells; however, HTLV-1 provirus is predominantly found in peripheral CD4 T cells in vivo. Here we find that TCF1 and LEF1, two Wnt transcription factors that are specifically expressed in T cells, inhibit viral replication through antagonizing Tax functions. TCF1 and LEF1 can each interact with Tax and inhibit Tax-dependent viral expression and activation of NF-κB and AP-1. As a result, HTLV-1 replication is suppressed in the presence of either TCF1 or LEF1. On the other hand, T-cell activation suppresses the expression of both TCF1 and LEF1, and this suppression enables Tax to function as an activator. We analyzed the thymus of a simian T-cell leukemia virus type 1 (STLV-1) infected Japanese macaque, and found a negative correlation between proviral load and TCF1/LEF1 expression in various T-cell subsets, supporting the idea that TCF1 and LEF1 negatively regulate HTLV-1 replication and the proliferation of infected cells. Thus, this study identified TCF1 and LEF1 as Tax antagonistic factors in vivo, a fact which may critically influence the peripheral T-cell tropism of this virus.

HTLV-1 Tax deregulates autophagy by recruiting autophagic molecules into lipid raft microdomains

The retroviral oncoprotein Tax from human T-cell leukemia virus type 1 (HTLV-1), an etiological factor that causes adult T-cell leukemia and lymphoma, has a crucial role in initiating T-lymphocyte transformation by inducing oncogenic signaling activation. We here report that Tax is a determining factor for dysregulation of autophagy in HTLV-1-transformed T cells and Tax-immortalized CD4 memory T cells. Tax facilitated autophagic process by activating inhibitor of κB (IκB) kinase (IKK) complex, which subsequently recruited an autophagy molecular complex containing Beclin1 and Bif-1 to the lipid raft microdomains. Tax engaged a crosstalk between IKK complex and autophagic molecule complex by directly interacting with both complexes, promoting assembly of LC3+ autophagosomes. Moreover, expression of lipid raft-targeted Bif-1 or Beclin1 was sufficient to induce formation of LC3+ autophagosomes, suggesting that Tax recruitment of autophagic molecules to lipid rafts is a dominant strategy to deregulate autophagy in the context of HTLV-1 transformation of T cells. Furthermore, depletion of autophagy molecules such as Beclin1 and PI3 kinase class III resulted in impaired growth of HTLV-1-transformed T cells, indicating a critical role of Tax-deregulated autophagy in promoting survival and transformation of virally infected T cells.

HTLV-1 induces a Th1-like state in CD4+CCR4+ T cells

Human T-lymphotropic virus type 1 (HTLV-1) is linked to multiple diseases, including the neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma. Evidence suggests that HTLV-1, via the viral protein Tax, exploits CD4+ T cell plasticity and induces transcriptional changes in infected T cells that cause suppressive CD4+CD25+CCR4+ Tregs to lose expression of the transcription factor FOXP3 and produce IFN-γ, thus promoting inflammation. We hypothesized that transformation of HTLV-1-infected CCR4+ T cells into Th1-like cells plays a key role in the pathogenesis of HAM/TSP. Here, using patient cells and cell lines, we demonstrated that Tax, in cooperation with specificity protein 1 (Sp1), boosts expression of the Th1 master regulator T box transcription factor (T-bet) and consequently promotes production of IFN-γ. Evaluation of CSF and spinal cord lesions of HAM/TSP patients revealed the presence of abundant CD4+CCR4+ T cells that coexpressed the Th1 marker CXCR3 and produced T-bet and IFN-γ. Finally, treatment of isolated PBMCs and CNS cells from HAM/TSP patients with an antibody that targets CCR4+ T cells and induces cytotoxicity in these cells reduced both viral load and IFN-γ production, which suggests that targeting CCR4+ T cells may be a viable treatment option for HAM/TSP.

Human T cell leukemia virus type I tax-induced IκB-ζ modulates tax-dependent and tax-independent gene expression in T cells

Human T cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T cell leukemia (ATL) and various inflammatory disorders including HTLV-I-associated myelopathy/tropical spastic paraparesis. HTLV-I oncoprotein Tax is known to cause permanent activation of many cellular transcription factors including nuclear factor-κB (NF-κB), cyclic adenosine 3',5'-monophosphate response element-binding protein, and activator protein 1 (AP-1). Here, we show that NF-κB-binding cofactor inhibitor of NF-κB-ζ (IκB-ζ) is constitutively expressed in HTLV-I-infected T cell lines and ATL cells, and Tax transactivates the IκB-ζ gene, mainly through NF-κB. Microarray analysis of IκB-ζ-expressing uninfected T cells demonstrated that IκB-ζ induced the expression of NF-κB. and interferon-regulatory genes such as B cell CLL/lymphoma 3 (Bcl3), guanylate-binding protein 1, and signal transducer and activator of transcription 1. The transcriptional activation domain, nuclear localization signal, and NF-κB-binding domain of IκB-ζ were required for Bcl3 induction, and IκB-ζ synergistically enhanced Tax-induced Bcl3 transactivation in an NF-κB-dependent manner. Interestingly, IκB-ζ inhibited Tax-induced NF-κB, AP-1 activation, and HTLV-I transcription. Furthermore, IκB-ζ interacted with Tax in vitro and this interaction was also observed in an HTLV-I-transformed T cell line. These results suggest that IκB-ζ modulates Tax-dependent and Tax-independent gene transcription in T cells. The function of IκB-ζ may be of significance in ATL genesis and pathogenesis of HTLV-I-associated diseases.

Preapoptotic protease calpain-2 is frequently suppressed in adult T-cell leukemia

Adult T-cell leukemia (ATL) is one of the most aggressive hematologic malignancies caused by human T-lymphotropic virus type 1 (HTLV-1) infection. The prognosis of ATL is extremely poor; however, effective strategies for diagnosis and treatment have not been established. To identify novel therapeutic targets and diagnostic markers for ATL, we employed focused proteomic profiling of the CD4(+)CD25(+)CCR4(+) T-cell subpopulation in which HTLV-1-infected cells were enriched. Comprehensive quantification of 14 064 peptides and subsequent 2-step statistical analysis using 29 cases (6 uninfected controls, 5 asymptomatic carriers, 9 HTLV-1-associated myelopathy/tropical spastic paraparesis patients, 9 ATL patients) identified 91 peptide determinants that statistically classified 4 clinical groups with an accuracy rate of 92.2% by cross-validation test. Among the identified 17 classifier proteins, α-II spectrin was drastically accumulated in infected T cells derived from ATL patients, whereas its digestive protease calpain-2 (CAN2) was significantly downregulated. Further cell cycle analysis and cell growth assay revealed that rescue of CAN2 activity by overexpressing constitutively active CAN2 (Δ(19)CAN2) could induce remarkable cell death on ATL cells accompanied by reduction of α-II spectrin. These results support that proteomic profiling of HTLV-1-infected T cells could provide potential diagnostic biomarkers and an attractive resource of therapeutic targets for ATL.

Dysregulation of TGF-beta signaling and regulatory and effector T-cell function in virus-induced neuroinflammatory disease

We previously demonstrated that CD4(+)CD25(+) T regulatory cells (Tregs), important for the maintenance of immune tolerance and prevention of autoimmune disease, from patients with human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) exhibit reduced Foxp3 expression and Treg suppressor function compared with healthy donors. Since TGF-beta signaling has been previously reported to be critical for both Foxp3 expression and Treg function, we examined whether this signaling pathway was dysregulated in patients with HAM/TSP. Levels of TGF-beta receptor II (TGF-betaRII) as well as Smad7 (a TGF-beta-inducible gene) were significantly reduced in CD4(+) T cells in patients with HAM/TSP compared with healthy donors, and the expression of TGF-betaRII inversely correlated with the HTLV-I tax proviral load. Importantly, both CD4(+)CD25(+) and CD4(+)CD25(-) T cells from HAM/TSP patients exhibited reduced TGF-betaRII expression compared with healthy donors, which was associated with functional deficits in vitro, including a block in TGF-beta-inducible Foxp3 expression that inversely correlated with the HTLV-I tax proviral load, loss of Treg suppressor function, and escape of effector T cells from Treg-mediated control. This evidence suggests that a virus-induced breakdown of immune tolerance affecting both regulatory and effector T cells contributes to the pathogenesis of HAM/TSP.

Fyn is a novel target of (-)-epigallocatechin gallate in the inhibition of JB6 Cl41 cell transformation

The cancer preventive action of (-)-epigallocatechin gallate (EGCG), found in green tea, is strongly supported by epidemiology and laboratory research data. However, the mechanism by which EGCG inhibits carcinogenesis and cell transformation is not clear. In this study, we report that EGCG suppressed epidermal growth factor (EGF)-induced cell transformation in JB6 cells. We also found that EGCG inhibited EGF-induced Fyn kinase activity and phosphorylation in vitro and in vivo. Fyn was implicated in the process because EGF-induced JB6 cell transformation was inhibited by small interfering RNA (siRNA)-Fyn-JB6 cells. With an in vitro protein-binding assay, we found that EGCG directly bound with the GST-Fyn-SH2 domain but not the GST-Fyn-SH3 domain. The K(d) value for EGCG binding to the Fyn SH2 domain was 0.367 +/- 0.122 microM and B(max) was 1.35 +/- 0.128 nmol/mg. Compared with control JB6 Cl41 cells, EGF-induced phosphorylation of p38 MAP kinase (p38 MAPK) (Thr180/Tyr182), ATF-2 (Thr71) and signal transducer and activator of transcription 1 (STAT1) (Thr727) was decreased in siRNA-Fyn-JB6 cells. EGCG could inhibit the phosphorylation of p38 MAPK, ATF-2, and STAT1. The DNA binding ability of AP-1, STAT1, and ATF-2 was also decreased in siRNA-Fyn-JB6 cells. Overall, these results demonstrated that EGCG interacted with Fyn and inhibited Fyn kinase activity and thereby regulated EGF-induced cell transformation. Inhibition of Fyn kinase activity is a novel and important mechanism that may be involved in EGCG-induced inhibition of cell transformation.

Human T-cell leukemia virus type-I Tax induces expression of interleukin-6 receptor (IL-6R): Shedding of soluble IL-6R and activation of STAT3 signaling

Human T-cell leukemia virus type-I (HTLV-I) encodes for the viral protein Tax, which is known to significantly disrupt transcriptional control of cytokines, cytokine receptors and other immuno-modulatory proteins in T cells. Specific dysregulation of these factors can alter the course and pathogenesis of infection. Soluble interleukin-6 receptor (sIL-6R) was shown to circulate at elevated levels in HTLV-I-infected patients, and high expressions of IL-6R and sIL-6R by HTLV-I-infected T cells were clinically and experimentally associated with Tax activity. To examine roles of Tax in expression of the IL-6R gene, the JPX-9 cell line was used, which is derived from Jurkat cell line expressing Tax cDNA. Over-expression of Tax enhanced IL-6R expression but not in Tax mutant JPX-9/M cell line. The clinical relevance of these observations was further demonstrated by ELISA using sera obtained from HTLV-I-infected patients. Our results revealed that sIL-6R levels were apparently elevated in HAM/TSP patients who were expressing Tax in their cells, while ATL patients' cells barely expressed Tax. HTLV-I-infected T-cell lines stimulated by IL-6/sIL-6R showed gp130-mediated STAT3 activity. IL-6/sIL-6R enhanced proliferation of HTLV-I-infected T cells in association with activation of STAT3. Consequently, Tax-mediated regulations of IL-6R and sIL-6R observed in HTLV-I-associated disorders may contribute to proliferation of HTLV-I-infected T cells through activation of inducible STAT3, and ultimately affect malignant growth and transformation of T cells by HTLV-I.

Inhibition of constitutively active Jak-Stat pathway suppresses cell growth of human T-cell leukemia virus type 1-infected T-cell lines and primary adult T-cell leukemia cells

Background

Human T-cell leukemia virus type 1 (HTLV-1), the etiologic agent for adult T-cell leukemia (ATL), induces cytokine-independent proliferation of T-cells, associated with the acquisition of constitutive activation of Janus kinases (Jak) and signal transducers and activators of transcription (Stat) proteins. Our purposes in this study were to determine whether activation of Jak-Stat pathway is responsible for the proliferation and survival of ATL cells, and to explore mechanisms by which inhibition of Jak-Stat pathway kills ATL cells.

Results

Constitutive activation of Stat3 and Stat5 was observed in HTLV-1-infected T-cell lines and primary ATL cells, but not in HTLV-1-negative T-cell lines. Using AG490, a Jak-specific inhibitor, we demonstrated that the activation of Stat3 and Stat5 was mediated by the constitutive phosphorylation of Jak proteins. AG490 inhibited the growth of HTLV-1-infected T-cell lines and primary ATL cells by inducing G₁ cell-cycle arrest mediated by altering the expression of cyclin D2, Cdk4, p53, p21, Pim-1 and c-Myc, and by apoptosis mediated by the reduced expression of c-IAP2, XIAP, survivin and Bcl-2. Importantly, AG490 did not inhibit the growth of normal peripheral blood mononuclear cells.

Conclusion

Our results indicate that activation of Jak-Stat pathway is responsible for the proliferation and survival of ATL cells. Inhibition of this pathway may provide a new approach for the treatment of ATL.

Curcumin induces growth-arrest and apoptosis in association with the inhibition of constitutively active JAK-STAT pathway in T cell leukemia

Adult T cell leukemia is an aggressive and frequently fatal malignancy that expressess constitutively activated growth-signaling pathways in association with deregulated growth and resistance to apoptosis. Curcumin (diferuloylmethane) is a naturally occurring yellow pigment, isolated from the rhizomes of the plant Curcuma longa that has traditionally been used in the treatment of injury and inflammation. But the effect and mechanism of action of curcumin on T cell leukemia is not known. To investigate the antitumor activity of curcumin in T cell leukemia, we examined its effect on constitutive phosphorylation of JAK and STAT proteins, proliferation, and apoptosis in HTLV-I-transformed T cell lines. HTLV-I-transformed T cell leukemia lines, MT-2, HuT-102, and SLB-1, express constitutively phosphorylated JAK3, TYK2, STAT3, and STAT5 signaling proteins. In vitro treatment with curcumin induced a dose-dependent decrease in JAK and STAT phosphorylation resulting in the induction of growth-arrest and apoptosis in T cell leukemia. The induction of growth-arrest and apoptosis in association with the blockade of constitutively active JAK-STAT pathway suggests this be a mechanism by which curcumin induces antitumor activity in T cell leukemia.

Deregulation of cell-signaling pathways in HTLV-1 infection

Human T-lymphotropic virus type 1 (HTLV-1) infection is associated with the clonal expansion and transformation of mature T lymphocytes. While the mechanisms involved are incompletely understood the viral regulatory protein Tax plays a central role in these processes. Recent studies employing genomic and proteomic approaches have demonstrated the marked complexity of gene deregulation associated with Tax expression and confirmed the remarkable pleiotropism of this protein as evidenced by the numerous Tax-cellular protein interactions in infected cells. In this review, we summarize the role of Tax in the deregulation of selected cellular-signaling pathways. Specifically, this has focused on the influence and interaction of Tax with the AP-1 and NF-AT transcription factors, PDZ domain-containing proteins, Rho-GTPases, and the Janus kinase/signal transducer and activator of transcription and transforming growth factor-beta-signaling pathways. In addition to identifying the deregulation of events within these pathways, attempts have been made to highlight differences between HTLV-1 and -2, which may relate to differences in their pathogenic properties.

The human T-cell lymphoma/leukemia viruses

The primate T-cell lymphoma/leukemia viruses belong to an oncogenic genus of complex retroviruses. Members of this genus have been shown to be pathogenic in man. The human T-cell lymphoma/leukemia virus (HTLV) type I has been linked in the etiology of T-cell malignancies and "autoimmune-like" neurologic and rheumatic disorders; a related virus, HTLV-II, is becoming increasingly associated with similar disorders. Cell transformation is thought to be caused predominantly by the effects of the viral regulatory protein, Tax. An additional induced host cell molecule, adult T-cell lymphoma-derived factor, may contribute to cell immortalization. Like the DNA tumor viruses, HTLV activates transcription of cellular proto-oncogenes and inhibits cellular mechanisms of tumor suppression, cell cycle arrest, and apoptosis. However, individuals who are able to mount a strong cell-mediated immune response and limit viral entry into uninfected cells do not develop associated malignancies. Unfortunately, HTLV-induced malignancies are difficult to treat with conventional chemotherapy, and disease progression is often rapid with a median survival of less than 2 years. There are, however, some novel approaches that have yet to be fully tested that may have greater efficacy in the treatment of HTLV-induced diseases. In the future, better screening and detection methods, along with new vaccines and therapies, may contribute to the increased prevention and control of HTLV infection and its associated diseases.

Constitutive activation of Stat5a by retrovirus integration in early pre-B lymphomas of SL/Kh strain mice

We found that the second intron of Stat5a was one of the common integration sites of the endogenous ecotropic murine leukemia virus, i.e., SL/Kh virus integration-1 (Svi1), in early pre-B lymphomas in SL/Kh mice. The high expression of STAT5A induced by Svi1 integration and activation accelerated the transcription of its target genes such as c-Myc. Transfection of the constitutively active Stat5a mutant cDNA, but not of the wild-type cDNA, to the bone marrow cells induced colony formation of pre-B cells in a methylcellulose medium and escaped from dependence on IL-7. Such growth depended on a genetic factor in the SL/Kh strain. Consitutively high expression of Stat5a either by retrovirus integration or transfection of active mutant cDNA can be lymphomagenic to early pre-B cells in collaboration with a certain genetic background factor of mice.

Human T-cell lymphotropic virus type I Tax activates lung resistance-related protein expression in leukemic clones established from an adult T-cell leukemia patient

OBJECTIVE

We examined the significance of human T-cell lymphotropic virus type I (HTLV-I) Tax protein-induced resistance to anticancer drugs and the relationship between Tax and multidrug resistance proteins.

MATERIALS AND METHODS

S1T cell, a leukemic non-Tax-producing T-cell clone established from an adult T-cell leukemia (ATL) patient, S1TcTax05 and S1TcTax10 clones, transfected with Tax stably expressing cDNA, and S1Tneo, transfected with a neomycin-resistant gene, were examined for Tax-related anticancer drug resistance. Resistance of those cells to the anticancer drugs doxorubicin, etoposide, cisplatin, and vindesine was tested with the MTT method. Expression of multidrug resistance protein mRNAs (MDR1, MRP1, cMOAT/MRP2, and LRP) was analyzed with reverse transcriptase polymerase chain reaction (RT-PCR). Doxorubicin subcellular distribution in those cells was examined by fluorescence microscopy.

RESULTS

S1TcTax05 and S1TcTax10 showed resistance to doxorubicin, etoposide, and vindesine, but not to cisplatin as compared with S1T or S1Tneo. RT-PCR demonstrated that MRP1 mRNA was expressed, but MDR1, cMOAT, and LRP mRNAs were not in S1T or S1Tneo. Marked expression of LRP mRNA was detected, but no change of MDR1, MRP1, or cMOAT mRNA expression in Tax-expressing S1TcTax05 and S1TcTax10. Fluorescence microscopy demonstrated that doxorubicin was distributed mainly in the cytoplasm of S1TcTax05 and S1TcTax10, and in the nucleus of S1T and S1Tneo.

CONCLUSIONS

These findings suggest that Tax-related drug resistance of ATL cells is due to LRP and not MDR1, as reported previously. These findings in cells derived from an ATL patient suggest a novel mechanism for drug resistance in Tax-expressing ATL cells.

Identification of novel targets of immunosuppressive agents by cDNA-based microarray analysis

The immunosuppressive agents cyclosporin A (CsA) and tacrolimus (FK506) bind to unrelated intracellular immunophilin receptors, cyclophilin (CyP) and FK506-binding protein (FKBP), respectively. The complexes of CsA-CyP and of FK506-FKBP both bind to and inhibit the activity of the calcium/calmodulin-dependent serine/threonine phosphatase calcineurin. We used cDNA microarray analysis to characterize early human peripheral blood T cell transcriptional responses following antigen receptor stimulation in the absence or presence of CsA or FK506, hoping to identify novel targets dependent upon calcineurin or immunophilins or, perhaps, specific targets of either CyP or FKBP inhibitable by one drug alone. The array data failed to identify genes uniquely sensitive to only one drug, suggesting that transcriptionally regulated, immunophilin-dependent but calcineurin-independent targets fell below the limits of detection in this system. In contrast, transcript profiling identified and mRNA and protein analysis confirmed novel as well as known genes reproducibly induced or inhibited by both immunosuppressive agents. In this context, we show that transcriptional activation of Stat5a and repression of the cytokine interleukin-16 are regulated by T cell receptor engagement and dependent upon drug-immunophilin complexes and, presumably, calcineurin activity.

IL-2 independent transformation of a unique human T cell line, TY8-3, and its subclones by HTLV-I and -II

Human T cell leukemia virus type I (HTLV-I) is etiologically associated with adult T cell leukemia (ATL) and chronic neurological disease, tropical spastic paraparesis (TSP). In our study, a unique IL-2 dependent human T cell line, designated TY8-3, was established from a thymoma obtained from a myasthenia gravis patient. The cells were heterogeneous and mainly consisted of those with CD4 , CD8 as well as activation markers and adhesion molecules including IL-2Ralpha,beta,gamma, CD45RO, Tf-R, HLA-DR, LFA-1alpha,beta, LFA-3, ICAM-1 and OX40 but without CD3 surface markers. Furthermore, these cells underwent an efficient and reproducible IL-2 independent transformation upon cocultivation with HTLV-I/II producing cell lines. Interestingly, although the infected cells became IL-2 independent, the growth rate of infected cells was significantly lower than those of parental TY8-3 cells. Clonal HTLV-I proviral DNA and viral particles were detected in the cells. Down-regulation of the lck and fyn genes and activation of the lyn gene was demonstrated in the IL-2 independent HTLV-positive TY8-3 cells. Subclones of TY8-3 cells were again able to be efficiently transformed and became IL-2 independent several months after coculture. Our results thus exhibit that TY8-3 cells and its subclones provide us with a very unique model whereby IL-2 independent transformation events of human T cells by HTLV-I/II in vitro can be studied at a clonal level.

Lentivirus infection in the brain induces matrix metalloproteinase expression: role of envelope diversity

Infection of the brain by lentiviruses, including human immunodeficiency virus (HIV) and feline immunodeficiency virus (FIV), causes inflammation and results in neurodegeneration. Molecular diversity within the lentivirus envelope gene has been implicated in the regulation of cell tropism and the host response to infection. Here, we examine the hypothesis that envelope sequence diversity modulates the expression of host molecules implicated in lentivirus-induced brain disease, including matrix metalloproteinases (MMP) and related transcription factors. Infection of primary macrophages by chimeric HIV clones containing brain-derived envelope fragments from patients with HIV-associated dementia (HAD) or nondemented AIDS patients (HIV-ND) showed that MMP-2 and -9 levels in conditioned media were significantly higher for the HAD clones. Similarly, STAT-1 and JAK-1 levels were higher in macrophages infected by HAD clones. Infections of primary feline macrophages by the neurovirulent FIV strain (V(1)CSF), the less neurovirulent strain (Petaluma), and a chimera containing the V(1)CSF envelope in a Petaluma background (FIV-Ch) revealed that MMP-2 and -9 levels were significantly higher in conditioned media from V(1)CSF- and FIV-Ch-infected macrophages, which was associated with increased intracellular STAT-1 and JAK-1 levels. The STAT-1 inhibitor fludarabine significantly reduced MMP-2 expression, but not MMP-9 expression, in FIV-infected macrophages. Analysis of MMP mRNA and protein levels in brain samples from HIV-infected persons or FIV-infected cats showed that MMP-2 and -9 levels were significantly increased in lentivirus-infected brains compared to those of uninfected controls. Elevated MMP expression was accompanied by significant increases in STAT-1 and JAK-1 mRNA and protein levels in the same brain samples. The present findings indicate that two lentiviruses, HIV and FIV, have common mechanisms of MMP-2 and -9 induction, which is modulated in part by envelope sequence diversity and the STAT-1/JAK-1 signaling pathway.

STAT proteins as novel targets for cancer therapy. Signal transducer an activator of transcription

Although the signal transducer and activator of transcription (STAT) proteins were originally discovered through the study of interferon-induced responses, a large number of cytokines and growth factors have been found to activate STATs. In addition to the fundamental role of STAT pathways in normal cell signaling, accumulating evidence is defining a critical role for STATs in oncogenesis. STAT family members are constitutively activated by various oncoproteins in transformed cells and are found activated in a wide variety of human tumors, including breast cancer and diverse blood malignancies. This review discusses recent progress in understanding how aberrant activation of STAT signaling pathways participates in malignant progression of human cancers. Current evidence indicates that one mechanism by which STATs contribute to oncogenesis involves prevention of programmed cell death, or apoptosis, thereby conferring a survival advantage and, potentially, resistance to chemotherapy. These advances identify STATs as novel molecular targets for development of promising therapeutics against human cancers that harbor activated STAT proteins.