Negative regulation of the SH2-homology containing protein-tyrosine phosphatase-1 (SHP-1) P2 promoter by the HTLV-1 Tax oncoprotein

Consideration of SHP-1 as a Molecular Target for Tumor Therapy

Abnormal activation of receptor tyrosine kinases (RTKs) contributes to tumorigenesis, while protein tyrosine phosphatases (PTPs) contribute to tumor control. One of the most representative PTPs is Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1), which is associated with either an increased or decreased survival rate depending on the cancer type. Hypermethylation in the promoter region of PTPN6, the gene for the SHP-1 protein, is a representative epigenetic regulation mechanism that suppresses the expression of SHP-1 in tumor cells. SHP-1 comprises two SH2 domains (N-SH2 and C-SH2) and a catalytic PTP domain. Intramolecular interactions between the N-SH2 and PTP domains inhibit SHP-1 activity. Opening of the PTP domain by a conformational change in SHP-1 increases enzymatic activity and contributes to a tumor control phenotype by inhibiting the activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT3) pathway. Although various compounds that increase SHP-1 activation or expression have been proposed as tumor therapeutics, except sorafenib and its derivatives, few candidates have demonstrated clinical significance. In some cancers, SHP-1 expression and activation contribute to a tumorigenic phenotype by inducing a tumor-friendly microenvironment. Therefore, developing anticancer drugs targeting SHP-1 must consider the effect of SHP-1 on both cell biological mechanisms of SHP-1 in tumor cells and the tumor microenvironment according to the target cancer type. Furthermore, the use of combination therapies should be considered.

Genetic profiling and biomarkers in peripheral T-cell lymphomas: current role in the diagnostic work-up

Peripheral T-cell lymphomas are a heterogeneous, and usually aggressive, group of mature T-cell neoplasms with overlapping clinical, morphologic and immunologic features. A large subset of these neoplasms remains unclassifiable with current diagnostic methods ("not otherwise specified"). Genetic profiling and other molecular tools have emerged as widely applied and transformative technologies for discerning the biology of lymphomas and other hematopoietic neoplasms. Although the application of these technologies to peripheral T-cell lymphomas has lagged behind B-cell lymphomas and other cancers, molecular profiling has provided novel prognostic and diagnostic markers as well as an opportunity to understand the biologic mechanisms involved in the pathogenesis of these neoplasms. Some biomarkers are more prevalent in specific T-cell lymphoma subsets and are being used currently in the diagnosis and/or risk stratification of patients with peripheral T-cell lymphomas. Other biomarkers, while promising, need to be validated in larger clinical studies. In this review, we present a summary of our current understanding of the molecular profiles of the major types of peripheral T-cell lymphoma. We particularly focus on the use of biomarkers, including those that can be detected by conventional immunohistochemical studies and those that contribute to the diagnosis, classification, or risk stratification of these neoplasms.

Hepatitis C Virus Core Protein Down-Regulates Expression of Src-Homology 2 Domain Containing Protein Tyrosine Phosphatase by Modulating Promoter DNA Methylation

Hepatitis C virus (HCV) is the major causative pathogen associated with liver cirrhosis and hepatocellular carcinoma. The main virion component, the core (C) protein, has been implicated in several aspects of HCV pathology including oncogenesis and immune subversion. Here we show that expression of the C protein induced specific tyrosine phosphorylation of the TCR-related signaling proteins ZAP-70, LAT and PLC-γ in the T cells. Stable expression of the C protein specifically reduced Src homology domain 2-containing protein tyrosine phosphatase 1 (SHP-1) mRNA and protein accumulation. Quantitative CpG methylation analysis revealed a distinct CpG methylation pattern at the SHP-1 gene promoter in the C protein expressing cells that included specific hypermethylation of the binding site for Sp1 transcription factor. Collectively, our results suggest that HCV may suppress immune responses and facilitate its own persistence by deregulating phosphotyrosine signaling via repressive epigenetic CpG modification at the SHP-1 promoter in the T cells.

Viral Manipulation of the Host Epigenome as a Driver of Virus-Induced Oncogenesis

Tumorigenesis due to viral infection accounts for a high fraction of the total global cancer burden (15–20%) of all human cancers. A comprehensive understanding of the mechanisms by which viral infection leads to tumor development is extremely important. One of the main mechanisms by which viruses induce host cell proliferation programs is through controlling the host’s epigenetic machinery. In this review, we dissect the epigenetic pathways through which oncogenic viruses can integrate their genome into host cell chromosomes and lead to tumor progression. In addition, we highlight the potential use of drugs based on histone modifiers in reducing the global impact of cancer development due to viral infection.

Peripheral T cell lymphomas: from the bench to the clinic

Peripheral T cell lymphomas (PTCLs) are a heterogeneous group of orphan neoplasms. Despite the introduction of anthracycline-based chemotherapy protocols, with or without autologous haematopoietic transplantation and a plethora of new agents, the progression-free survival of patients with PTCLs needs to be improved. The rarity of these neoplasms, the limited knowledge of their driving defects and the lack of experimental models have impaired clinical successes. This scenario is now rapidly changing with the discovery of a spectrum of genomic defects that hijack essential signalling pathways and foster T cell transformation. This knowledge has led to new genomic-based stratifications, which are being used to establish objective diagnostic criteria, more effective risk assessment and target-based interventions. The integration of genomic and functional data has provided the basis for targeted therapies and immunological approaches that underlie individual tumour vulnerabilities. Fortunately, novel therapeutic strategies can now be rapidly tested in preclinical models and effectively translated to the clinic by means of well-designed clinical trials. We believe that by combining new targeted agents with immune regulators and chimeric antigen receptor-expressing natural killer and T cells, the overall survival of patients with PTCLs will dramatically increase.

Novel insights into the pathogenesis of T-cell lymphomas

T-cell lymphomas are a heterogeneous group of rare malignancies with overlapping clinical, immunologic, and histologic features. Recent advances in our understanding of T-cell differentiation based on gene expression profiling, next-generation sequencing, and transgenic mouse modeling studies have better elucidated the pathogenetic mechanisms underlying the diverse biology of T-cell lymphomas. These studies show that although genetic alterations in epigenetic modifiers are implicated in all subtypes of T-cell lymphomas, specific subtypes demonstrate enrichment for particular recurrent alterations targeting specific genes. In this regard, RHOA and TET2 alterations are prevalent in nodal T-cell lymphomas, particularly angioimmunoblastic T-cell lymphomas, peripheral T-cell lymphomas (PTCLs) not otherwise specified, and nodal PTCLs with T-follicular helper phenotype. JAK-STAT signaling pathways are mutationally activated in many extranodal T-cell lymphomas, such as natural killer/T-cell and hepatosplenic T-cell lymphomas. The functional significance of many of these genetic alterations is becoming better understood. Altogether these advances will continue to refine diagnostic criteria, improve prognostication, and identify novel therapeutic targets, resulting in improved outcomes for patient with T-cell lymphomas.

Implication of protein tyrosine phosphatase SHP-1 in cancer-related signaling pathways

The altered expression of SHP-1 (SH2 domain-containing protein tyrosine phosphatase) as a consequence of promoter hypermethylation or mutations has evidently been linked to cancer development. The notion of being a cancer drug target is conceivable as SHP-1 negatively regulates cell cycle and inflammatory pathways which are an inevitable part of oncogenic transformation. In the present review, we try to critically analyze the role of SHP-1 in cancer progression via regulating the above mentioned pathways with the major emphasis on cell cycle components and JAK/STAT pathway, commencing with the SHP-1 biology in immune cell signaling. Lastly, we have provided the future directions for researchers to encourage SHP-1 as a prognostic marker and curative target for this debilitating disease called as cancer.

Update on microbe-induced epigenetic changes: bacterial effectors and viral oncoproteins as epigenetic dysregulators

Pathoepigenetics is a new discipline describing how disturbances in epigenetic regulation alter the epigenotype and gene-expression pattern of human, animal or plant cells. Such ‘epigenetic reprogramming’ may play an important role in the initiation and progression of a wide variety of diseases. Infectious diseases also belong to this category: recent data demonstrated that microbial pathogens, including bacteria and viruses, are capable of dysregulating the epigenetic machinery of their host cell. The resulting heritable changes in host cell gene expression may favor the colonization, growth or spread of infectious pathogens. It may also facilitate the establishment of latency and malignant cell transformation. In this article, we review how bacterial epigenetic effectors and inflammatory processes elicited by bacteria alter the host cell epigenotype, and describe how oncoproteins encoded by human tumor viruses act as epigenetic dysregulators to alter the phenotype and behavior of host cells.

Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation

Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the 'normal' epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing.

Human T-lymphotropic virus proteins and post-translational modification pathways

Cell life from the cell cycle to the signaling transduction and response to stimuli is finely tuned by protein post-translational modifications (PTMs). PTMs alter the conformation, the stability, the localization, and hence the pattern of interactions of the targeted protein. Cell pathways involve the activation of enzymes, like kinases, ligases and transferases, that, once activated, act on many proteins simultaneously, altering the state of the cell and triggering the processes they are involved in. Viruses enter a balanced system and hijack the cell, exploiting the potential of PTMs either to activate viral encoded proteins or to alter cellular pathways, with the ultimate consequence to perpetuate through their replication. Human T-lymphotropic virus type 1 (HTLV-1) is known to be highly oncogenic and associates with adult T-cell leukemia/lymphoma, HTLV-1-associated myelopathy/tropical spastic paraparesis and other inflammatory pathological conditions. HTLV-1 protein activity is controlled by PTMs and, in turn, viral activity is associated with the modulation of cellular pathways based on PTMs. More knowledge is acquired about the PTMs involved in the activation of its proteins, like Tax, Rex, p12, p13, p30, HTLV-I basic leucine zipper factor and Gag. However, more has to be understood at the biochemical level in order to counteract the associated fatal outcomes. This review will focus on known PTMs that directly modify HTLV-1 components and on enzymes whose activity is modulated by viral proteins.

Increased promoter methylation of the immune regulatory gene SHP-1 in leukocytes of multiple sclerosis subjects

The protein tyrosine phosphatase, SHP-1, is a negative regulator of proinflammatory signaling and autoimmune disease. We have previously reported reduced SHP-1 expression in peripheral blood leukocytes of subjects with multiple sclerosis (MS). Recent evidence indicates that virus-induced DNA methylation of the SHP-1 promoter is responsible for aberrant silencing of SHP-1 expression and function in hematopoietic cells that might relate to inflammatory diseases. In the present study, bisulfite sequencing of the SHP-1 promoter demonstrated that over a third of MS subjects had abnormally high promoter methylation. As SHP-1 is deficient in MS leukocytes and SHP-1-regulated proinflammatory genes are correspondingly upregulated, we propose that increased SHP-1 promoter methylation may relate in part to decreased SHP-1 expression and increased leukocyte-mediated inflammation in MS.

Direct inhibition of RNAse T2 expression by the HTLV-1 viral protein Tax

Adult T-cell leukemia (ATL) is one of the primary diseases caused by Human T-cell Leukemia Virus type 1 (HTLV-1) infection. The virally-encoded Tax protein is believed to initiate early events in the development of this disease, as it is able to promote immortalization of T-cells and transformation of other cell types. These processes may be aided by the ability of the viral protein to directly deregulate expression of specific cellular genes through interactions with numerous transcriptional regulators. To identify gene promoters where Tax is localized, we isolated Tax-DNA complexes from an HTLV-1-infected T-cell line through a chromatin immunoprecipitation (ChIP) assay and used the DNA to probe a CpG island microarray. A site within the RNASET2 gene was found to be occupied by Tax. Real-time PCR analysis confirmed this result, and transient expression of Tax in uninfected cells led to the recruitment of the viral protein to the promoter. This event correlated with a decrease in the level of RNase T2 mRNA and protein, suggesting that Tax represses expression of this gene. Loss of RNase T2 expression occurs in certain hematological malignancies and other forms of cancer, and RNase T2 was recently reported to function as a tumor suppressor. Consequently, a reduction in the level of RNase T2 by Tax may play a role in ATL development.

The phosphatase Shp2 is required for signaling by the Kaposi's sarcoma-associated herpesvirus viral GPCR in primary endothelial cells

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma (KS), an AIDS-related endothelial cell malignancy that is the most common cancer in central and southern Africa. The KSHV viral G protein-coupled receptor (vGPCR) is a viral oncogene that conveys a survival advantage to endothelial cells and causes KS-like tumors in mouse models. In this study we investigate the role of Shp2, a protein tyrosine phosphatase in vGPCR signaling. Shp2 is vital to many cytokine-induced signaling pathways and is dysregulated in various infections and malignancies. It has also recently been implicated in angiogenesis. We find that vGPCR activity results in phosphorylation of regulatory tyrosines in Shp2 and that in turn, Shp2 is required for vGPCR-mediated activation of MEK, NFkappaB, and AP-1. Furthermore, both genetic and chemical inhibition of Shp2 abrogate vGPCR-induced enhancement of endothelial cell migration. This establishes Shp2 as an important point of convergence of KSHV vGPCR signaling and a potential molecular target in the design of an anti-KSHV therapeutic regimen.

Functional interaction of HTLV-1 tax protein with the POZ domain of the transcriptional repressor BCL6

The Tax protein encoded by human T-cell leukaemia virus type 1 (HTLV-1) has a pivotal role in T-cell transformation by deregulating cellular signalling pathways. Using the yeast two-hybrid system to screen a human leukocyte cDNA library, we identified BCL6 (B-cell lymphoma 6) as a cellular protein, which interacts with Tax 1. The BCL6 gene encodes a sequence-specific transcriptional repressor that contains a conserved N-terminal poxvirus and zinc finger (POZ) repressor domain and a C-terminal Kruppel-like zinc finger DNA binding domain. Using both in vivo and in vitro methods, we demonstrate that the POZ domain of BCL6 is sufficient for its interaction with Tax 1. Using functional assays, we demonstrate that Tax 1 enhanced the repressive activity of BCL6 and increased the levels of apoptosis induced by BCL6 in osteosarcoma cells indicating that both proteins cooperate in vivo to cause a physiological affect. Furthermore, BCL6 recruited Tax 1 into punctate nuclear structures, which suggests that Tax 1 colocalizes with BCL6 in repressor complexes in vivo. BCL6 expression significantly downregulated both basal and Tax-induced nuclear factor-kappaB and long terminal repeat activation. This suggests that the expression of BCL6 in HTLV infected cells may contribute to the silencing of viral gene expression and to the long clinical latency associated with HTLV infection.

Macrophages of multiple sclerosis patients display deficient SHP-1 expression and enhanced inflammatory phenotype

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of proinflammatory cytokine signaling, TLR signaling, and inflammatory gene expression. Furthermore, mice genetically lacking SHP-1 (me/me) display a profound susceptibility to inflammatory CNS demyelination relative to wild-type mice. In particular, SHP-1 deficiency may act predominantly in inflammatory macrophages to increase CNS demyelination as SHP-1-deficient macrophages display coexpression of inflammatory effector molecules and increased demyelinating activity in me/me mice. Recently, we reported that PBMCs of multiple sclerosis (MS) patients have a deficiency in SHP-1 expression relative to normal control subjects indicating that SHP-1 deficiency may play a similar role in MS as to that seen in mice. Therefore, it became essential to examine the specific expression and function of SHP-1 in macrophages from MS patients. Herein, we document that macrophages of MS patients have deficient SHP-1 protein and mRNA expression relative to those of normal control subjects. To examine functional consequences of the lower SHP-1, the activation of STAT6, STAT1, and NF-kappaB was quantified and macrophages of MS patients showed increased activation of these transcription factors. In accordance with this observation, several STAT6-, STAT1-, and NF-kappaB-responsive genes that mediate inflammatory demyelination were increased in macrophages of MS patients following cytokine and TLR agonist stimulation. Supporting a direct role of SHP-1 deficiency in altered macrophage function, experimental depletion of SHP-1 in normal subject macrophages resulted in an increased STAT/NF-kappaB activation and increased inflammatory gene expression to levels seen in macrophages of MS patients. In conclusion, macrophages of MS patients display a deficiency of SHP-1 expression, heightened activation of STAT6, STAT1, and NF-kappaB and a corresponding inflammatory profile that may be important in controlling macrophage-mediated demyelination in MS.

Mechanisms of SHP-1 P2 promoter regulation in hematopoietic cells and its silencing in HTLV-1-transformed T cells

The Src homology-2-containing protein-tyrosine phosphatase 1 (SHP-1), is a negative regulator of cell signaling. It is also considered a tumor suppressor gene because of its ability to antagonize the action of tyrosine kinases. Although SHP-1 is expressed strongly in hematopoietic cells, decreased expression has been observed in various hematological malignancies, which suggests a central involvement of SHP-1 in leukemogenesis. We have shown previously that human T cell lymphotropic virus type-1 (HTLV-1) Tax-induced promoter silencing (TIPS) is an early event causing down-regulation of SHP-1 expression, which is dependent on NF-kappaB. In this study, DNase I footprinting and EMSA also revealed binding of transcription factors, specificity protein 1 (Sp1) and octamer-binding transcription factor 1 (Oct-1) to the P2 promoter, and site-directed mutagenesis confirmed that these factors contribute to the basal P2 promoter activity. Chromatin immunoprecipitation (CHIP) assays showed that Sp1, Oct-1, NF-kappaB, CREB-1, and RNA polymerase II interacted with the core SHP-1 P2 promoter in CD4+ T cells and Jurkat cells but not in HTLV-1-transformed MT-2 and HUT102 cells when HTLV-1 Tax is present. Furthermore, bisulfite sequencing of the SHP-1 P2 core region revealed heavy CpG methylation in HTLV-1-transformed cells compared with freshly isolated CD4+ T cells and HTLV-1-noninfected T cell lines. A significant inverse correlation between degree of CpG methylation and expression of SHP-1 mRNA or protein was observed. Taken together, our data support the notion that in HTLV-1-transformed CD4+ T cells, TIPS causes dissociation of transcription factors from the core SHP-1 P2 promoter, which in turn leads to subsequent DNA methylation, an important early step for leukemogenesis.

The HTLV-1 Tax interactome

The Tax1 oncoprotein encoded by Human T-lymphotropic virus type I is a major determinant of viral persistence and pathogenesis. Tax1 affects a wide variety of cellular signalling pathways leading to transcriptional activation, proliferation and ultimately transformation. To carry out these functions, Tax1 interacts with and modulates activity of a number of cellular proteins. In this review, we summarize the present knowledge of the Tax1 interactome and propose a rationale for the broad range of cellular proteins identified so far.

SHP-1 deficiency and increased inflammatory gene expression in PBMCs of multiple sclerosis patients

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and demyelination in central nervous system. The present study investigates a possible similar role for SHP-1 in the human disease multiple sclerosis (MS). The levels of SHP-1 protein and mRNA in PBMCs of MS patients were significantly lower compared to normal subjects. Moreover, promoter II transcripts, expressed from one of two known promoters, were selectively deficient in MS patients. To examine functional consequences of the lower SHP-1 in PBMCs of MS patients, we measured the intracellular levels of phosphorylated STAT6 (pSTAT6). As expected, MS patients had significantly higher levels of pSTAT6. Accordingly, siRNA to SHP-1 effectively increased the levels of pSTAT6 in PBMCs of controls to levels equal to MS patients. Additionally, transduction of PBMCs with a lentiviral vector expressing SHP-1 lowered pSTAT6 levels. Finally, multiple STAT6-responsive inflammatory genes were increased in PBMCs of MS patients relative to PBMCs of normal subjects. Thus, PBMCs of MS patients display a stable deficiency of SHP-1 expression, heightened STAT6 phosphorylation, and an enhanced state of activation relevant to the mechanisms of inflammatory demyelination.