Binding of c-Rel to STAT5 target sequences in HTLV-I-transformed T cells

Reprogramming of regulatory T cells in inflammatory tumor microenvironment: can it become immunotherapy turning point?

Overcoming the immunosuppressive tumor microenvironment and identifying widely used immunosuppressants with minimal side effects are two major challenges currently hampering cancer immunotherapy. Regulatory T cells (Tregs) are present in almost all cancer tissues and play an important role in preserving autoimmune tolerance and tissue homeostasis. The tumor inflammatory microenvironment causes the reprogramming of Tregs, resulting in the conversion of Tregs to immunosuppressive phenotypes. This process ultimately facilitates tumor immune escape or tumor progression. However, current systemic Treg depletion therapies may lead to severe autoimmune toxicity. Therefore, it is crucial to understand the mechanism of Treg reprogramming and develop immunotherapies that selectively target Tregs within tumors. This article provides a comprehensive review of the potential mechanisms involved in Treg cell reprogramming and explores the application of Treg cell immunotherapy. The interference with reprogramming pathways has shown promise in reducing the number of tumor-associated Tregs or impairing their function during immunotherapy, thereby improving anti-tumor immune responses. Furthermore, a deeper understanding of the mechanisms that drive Treg cell reprogramming could reveal new molecular targets for future treatments.

IgE-Induced Mast Cell Activation Is Suppressed by Dihydromyricetin through the Inhibition of NF-κB Signaling Pathway

Mast cells play a crucial role in the pathogenesis of type 1 allergic reactions by binding to IgE and allergen complexes and initiating the degranulation process, releasing pro-inflammatory mediators. Recently, research has focused on finding a stable and effective anti-allergy compound to prevent or treat anaphylaxis. Dihydromyricetin (DHM) is a flavonoid compound with several pharmacological properties, including free radical scavenging, antithrombotic, anticancer, and anti-inflammatory activities. In this study, we investigated the anti-allergic inflammatory effects and the underlying molecular mechanism of DHM in the DNP-IgE-sensitized human mast cell line, KU812. The cytokine levels and mast cell degranulation assays were determined by enzyme-linked immunosorbent assay (ELISA). The possible mechanism of the DHM-mediated anti-allergic signaling pathway was analyzed by western blotting. It was found that treatment with DHM suppressed the levels of inflammatory cytokines TNF-α and IL-6 in DNP-IgE-sensitized KU812 cells. The anti-allergic inflammatory properties of DHM were mediated by inhibition of NF-κB activation. In addition, DHM suppressed the phosphorylation of signal transducer and activator of transcription 5 (STAT5) and mast cell-derived tryptase production. Our study shows that DHM could mitigate mast cell activation in allergic diseases.

Superoxide-Generating Nox5α Is Functionally Required for the Human T-Cell Leukemia Virus Type 1-Induced Cell Transformation Phenotype

Human T-cell leukemia virus type 1 (HTLV-1) is associated with adult T-cell leukemia (ATL) and transforms T cells in vitro. To our knowledge, the functional role of reactive oxygen species (ROS)-generating NADPH oxidase 5 (Nox5) in HTLV-1 transformation remains undefined. Here, we found that Nox5α expression was upregulated in 88% of 17 ATL patient samples but not in normal peripheral blood T cells. Upregulation of the Nox5α variant was transcriptionally sustained by the constitutive Janus family tyrosine kinase (Jak)-STAT5 signaling pathway in interleukin-2 (IL-2)-independent HTLV-1-transformed cell lines, including MT1 and MT2, whereas it was transiently induced by the IL-2-triggered Jak-STAT5 axis in uninfected T cells. A Nox inhibitor, diphenylene iodonium, and antioxidants such as N-acetyl cysteine blocked proliferation of MT1 and MT2 cells. Ablation of Nox5α by small interfering RNAs abrogated ROS production, inhibited cellular activities, including proliferation, migration, and survival, and suppressed tumorigenicity in immunodeficient NOG mice. The findings suggest that Nox5α is a key molecule for redox-signal-mediated maintenance of the HTLV-1 transformation phenotype and could be a potential molecular target for therapeutic intervention in cancer development.

IMPORTANCE

HTLV-1 is the first human oncogenic retrovirus shown to be associated with ATL. Despite the extensive study over the years, the mechanism underlying HTLV-1-induced cell transformation is not fully understood. In this study, we addressed the expression and function of ROS-generating Nox family genes in HTLV-1-transformed cells. Our report provides the first evidence that the upregulated expression of Nox5α is associated with the pathological state of ATL peripheral blood mononuclear cells and that Nox5α is an integral component of the Jak-STAT5 signaling pathway in HTLV-1-transformed T cells. Nox5α-derived ROS are critically involved in the regulation of cellular activities, including proliferation, migration, survival, and tumorigenicity, in HTLV-1-transformed cells. These results indicate that Nox5α-derived ROS are functionally required for maintenance of the HTLV-1 transformation phenotype. The finding provides new insight into the redox-dependent mechanism of HTLV-1 transformation and raises an intriguing possibility that Nox5α serves as a potential molecular target to treat HTLV-1-related leukemia.

c-Rel in GVHD biology: a missing link

Graft-versus-host disease (GVHD) is a major complication associated with allogeneic bone marrow transplantation (BMT). Recent advances in the treatment of lymphoid malignancies with BMT include exploring mechanisms that can inhibit GVHD while maintaining graft-versus-leukemic (GVL) effects. In this issue of the European Journal of Immunology, Yu et al. [Eur. J. Immunol. 2013.43: 2327-2337] demonstrate efficient separation of GVHD and GVL by abrogating c-Rel in T cells. Intrinsic c-Rel deficiency in T cells resulted in complete protection against GVHD in both major and minor histocompatibility mismatched murine models of BMT. Protection against GVHD was associated with a decreased presence of Th1 and Th17 cells with a concomitant increase in Treg-cell numbers. Interestingly, an intrinsic defect of c-Rel also resulted in decreased expression of the Th1-associated chemokine receptor CXCR3. Finally, the absence of c-Rel maintained GVL effects with significant tumor clearance in murine recipients. These data suggest that specific targeting of the T-cell-specific transcription factor c-Rel can inhibit GVHD while maintaining GVL effects.

Nuclear factor-kappaB mediates the inhibitory effects of tumor necrosis factor-alpha on growth hormone-inducible gene expression in liver

TNF inhibits serine protease inhibitor 2.1 (Spi 2.1) and IGF-I gene expression by GH in CWSV-1 hepatocytes. The current study describes construction of a GH-inducible IGF-I promoter construct and investigates mechanisms by which TNF and nuclear factor-kappaB (NFkappaB) inhibit GH-inducible gene expression. CWSV-1 cells were transfected with GH-inducible Spi 2.1 or IGF-I promoter luciferase constructs, incubated with TNF signaling inhibitors (fumonisin B1 for sphingomyelinase and SP600125 for c-Jun N-terminal kinase), treated with or without TNF, and then stimulated with recombinant human GH. The 5- to 6-fold induction of Spi 2.1 and IGF-I promoter activity by GH was inhibited by TNF. Neither fumonisin B1 nor SP600125 prevented the inhibitory effects of TNF on GH-inducible promoter activity. Dominant-negative inhibitor-kappaBalpha (IkappaBalpha) expression vectors (IkappaBalphaS/A or IkappaBalphaTrunc), p65 and p50 expression vectors, and p65 deletion constructs were used to investigate the NFkappaB pathway. IkappaBalphaS/A and IkappaBalphaTrunc ameliorated the inhibitory effects of TNF on GH-inducible Spi 2.1 and IGF-I promoter activity. Cotransfection of CWSV-1 cells with expression vectors for p65 alone or p50 and p65 together inhibited GH-inducible Spi 2.1 and IGF-I promoter activity. Cotransfection with a C-terminal p65 deletion (1-450) enhanced GH-inducible promoter activity, whereas the N-terminal deletion (31-551) was inhibitory for IGF-I but not Spi 2.1. Cycloheximide did not antagonize the inhibitory effects of TNF on GH-inducible IGF-I expression. We conclude the inhibitory effects of TNF on GH-inducible promoter activity are mediated by NFkappaB, especially p65, by a mechanism that does not require protein synthesis.

Regulation of early wave of germ cell apoptosis and spermatogenesis by deubiquitinating enzyme CYLD

Spermatogenesis involves an early wave of germ cell apoptosis, which is required for maintaining the balance between germ cells and supporting Sertoli cells. However, the signaling mechanism regulating this apoptotic event is poorly defined. Here we show that genetic deficiency of Cyld, a recently identified deubiquitinating enzyme, attenuates the early wave of germ cell apoptosis and causes impaired spermatogenesis in mice. Interestingly, the loss of CYLD in testicular cells leads to activation of the transcription factor NF-kappaB and aberrant expression of antiapoptotic genes. We further show that CYLD negatively regulates a ubiquitin-dependent NF-kappaB activator, RIP1. CYLD binds to RIP1 and inhibits its ubiquitination and signaling function. These findings establish CYLD as a pivotal deubiquitinating enzyme (DUB) that regulates germ cell apoptosis and spermatogenesis and suggest an essential role for CYLD in controlling the RIP1/NF-kappaB signaling axis in testis.

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.

Stimulation of c-Rel transcriptional activity by PKA catalytic subunit beta

Nuclear factor kappaB (NF-kappaB) is a eukaryotic transcription factor which responds to different extracellular signals. It is involved in immune response, inflammation, and cell proliferation. Increased expression of c-Rel (or its viral homolog v-Rel), one component of the NF-kappaB factors, induces tumorigenesis in different systems. The activity of NF-kappaB can be regulated by protein kinase A (PKA) in a cAMP-independent manner. Our previous results showed that c-MYC induces the activity of PKA by inducing the transcription of the gene encoding the PKA catalytic subunit beta (PKA-Cbeta). Constitutive expression of PKA-Cbeta in Rat1a cells induces their transformation. Here we show that CREB is unlikely to be a phosphorylation target of PKA-Cbeta as characterized by different cell lines. Electrophoretic mobility shift assays showed that c-Rel is present as a significant component of the NF-kappaB factors in c-MYC overexpressing status. The transcriptional activity of c-Rel was significantly stimulated by PKA-Cbeta. Coactivators p300/CBP are at least partially responsible for the enhanced activation mediated by c-Rel and PKA-Cbeta. Interaction between c-Rel and PKA-Cbeta was demonstrated using coimmunoprecipitation assays. Immunoprecipitation-in vitro phosphorylation assays showed the direct phosphorylation of c-Rel by PKA-Cbeta. These results indicate that c-Rel is a reasonable phosphorylation target of PKA-Cbeta, and that the transcriptional activity of c-Rel is stimulated by PKA-Cbeta possibly through the interaction with p300/CBP.

Nuclear factor-kappaB modulation as a therapeutic approach in hematologic malignancies

Nuclear factor-kappaB (NF-kappaB) is a collective term that refers to a small class of dimeric transcription factors for a number of genes, including growth factors, angiogenesis modulators, cell-adhesion molecules, and antiapoptotic factors. Although most NF-kappaB proteins promote transcription, some act as inactivating or repressive complexes. The most common p50-RelA (p65) dimer known "specifically" as NF-kappaB, is relatively abundant, controls the expression of numerous genes, and exists as an inactive cytoplasmic complex bound to inhibitory proteins of the NF-kappaB inhibitor (IkappaB) family. The inactive NF-kappaB-IkappaB complex is activated by a variety of stimuli, including proinflammatory cytokines, mitogens, growth factors, and stress-inducing agents. The release of NF-kappaB facilitates its translocation to the nucleus, where it promotes cell survival by initiating the transcription of genes encoding stress-response enzymes, cell-adhesion molecules, proinflammatory cytokines, and antiapoptotic proteins. Constitutive activation of NF-kappaB in the nucleus is observed in some hematologic disorders. With the recent approval of bortezomib for patients with advanced multiple myeloma, NF-kappaB modulation is likely to be a therapeutic endeavor of increasing interest in coming years.

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.

A common functional C-T substitution polymorphism in the promoter region of the human catalase gene influences transcription factor binding, reporter gene transcription and is correlated to blood catalase levels

Oxidative stress is implicated in disease and aging. In order to obtain molecular genetic tools that can be used to determine the potential impact of oxidative stress we examined the human catalase gene promoter for possible variation. Genomic DNA isolated from 10 individuals was screened for polymorphisms in the 5'-flanking region by direct sequence analysis of PCR products (nt -307 to -46 from the transcription start site). A common C/T polymorphism -262 base pairs from the transcription start site was detected. Computer analysis indicated that the two variants bound different transcription factors. Indeed, gel retardation analysis revealed different protein binding patterns to the two variants. Expression studies with reporter constructs showed significantly higher transcriptional activity of the T variant in HepG2 and K562 cells (1.5-fold,p <.05 Wilcoxon test). Thus a higher expression in human liver and blood cells is possible. In order to test this hypothesis, catalase levels in red blood cells were determined in 29 donors. The corresponding genotype was determined with a restriction enzyme-based assay. It was found that catalase levels were significantly higher in donors carrying the T allele in comparison to donors homozygous for the C allele (p <.03). In conclusion, we report here the first common (allele frequency in a Swedish population, 28%) genetic variant in a fundamental oxidative stress protection gene with a defined phenotype.

Functional uncoupling of the Janus kinase 3-Stat5 pathway in malignant growth of human T cell leukemia virus type 1-transformed human T cells

Human T cell leukemia virus type 1 (HTLV-1) transforms cytokine-dependent T lymphocytes and causes adult T cell leukemia. Janus tyrosine kinase (Jak)3 and transcription factors Stat5a and Stat5b are essential for the proliferation of normal T cells and are constitutively hyperactivated in both HTLV-1-transformed human T cell lines and lymphocytes isolated from HTLV-1-infected patients; therefore, a critical role for the Jak3-Stat5 pathway in the progression of this disease has been postulated. We recently reported that tyrphostin AG-490 selectively blocked IL-2 activation of Jak3/Stat5 and growth of murine T cell lines. Here we demonstrate that disruption of Jak3/Stat5a/b signaling with AG-490 (50 microM) blocked the proliferation of primary human T lymphocytes, but paradoxically failed to inhibit the proliferation of HTLV-1-transformed human T cell lines, HuT-102 and MT-2. Structural homologues of AG-490 also inhibited the proliferation of primary human T cells, but not HTLV-1-infected cells. Disruption of constitutive Jak3/Stat5 activation by AG-490 was demonstrated by inhibition of 1) tyrosine phosphorylation of Jak3, Stat5a (Tyr(694)), and Stat5b (Tyr(699)); 2) serine phosphorylation of Stat5a (Ser(726)) as determined by a novel phosphospecific Ab; and 3) Stat5a/b DNA binding to the Stat5-responsive beta-casein promoter. In contrast, AG-490 had no effect on DNA binding by p50/p65 components of NF-kappaB, a transcription factor activated by the HTLV-1-encoded phosphoprotein, Tax. Collectively, these data suggest that the Jak3-Stat5 pathway in HTLV-1-transformed T cells has become functionally redundant for proliferation. Reversal of this functional uncoupling may be required before Jak3/Stat5 inhibitors will be useful in the treatment of this malignancy.