Mechanisms of NF-kappaB activation by the HTLV type 1 tax protein

Malignancy and viral infections in Sub-Saharan Africa: A review

The burden of malignancy related to viral infection is increasing in Sub-Saharan Africa (SSA). In 2018, approximately 2 million new cancer cases worldwide were attributable to infection. Prevention or treatment of these infections could reduce cancer cases by 23% in less developed regions and about 7% in developed regions. Contemporaneous increases in longevity and changes in lifestyle have contributed to the cancer burden in SSA. African hospitals are reporting more cases of cancer related to infection (e.g., cervical cancer in women and stomach and liver cancer in men). SSA populations also have elevated underlying prevalence of viral infections compared to other regions. Of 10 infectious agents identified as carcinogenic by the International Agency for Research on Cancer, six are viruses: hepatitis B and C viruses (HBV and HCV, respectively), Epstein-Barr virus (EBV), high-risk types of human papillomavirus (HPV), Human T-cell lymphotropic virus type 1 (HTLV-1), and Kaposi's sarcoma herpesvirus (KSHV, also known as human herpesvirus type 8, HHV-8). Human immunodeficiency virus type 1 (HIV) also facilitates oncogenesis. EBV is associated with lymphomas and nasopharyngeal carcinoma; HBV and HCV are associated with hepatocellular carcinoma; KSHV causes Kaposi's sarcoma; HTLV-1 causes T-cell leukemia and lymphoma; HPV causes carcinoma of the oropharynx and anogenital squamous cell cancer. HIV-1, for which SSA has the greatest global burden, has been linked to increasing risk of malignancy through immunologic dysregulation and clonal hematopoiesis. Public health approaches to prevent infection, such as vaccination, safer injection techniques, screening of blood products, antimicrobial treatments and safer sexual practices could reduce the burden of cancer in Africa. In SSA, inequalities in access to cancer screening and treatment are exacerbated by the perception of cancer as taboo. National level cancer registries, new screening strategies for detection of viral infection and public health messaging should be prioritized in SSA's battle against malignancy. In this review, we discuss the impact of carcinogenic viruses in SSA with a focus on regional epidemiology.

In Vivo Tumorigenesis, Osteolytic Sarcomas, and Tumorigenic Cell Lines from Transgenic Mice Expressing the Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Viral Oncogene

Human T-lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia, a disease commonly associated with hypercalcemia and osteolysis. There is no effective treatment for HTLV-1, and the osteolytic mechanisms are not fully understood. Mice expressing the HTLV-1 oncogene Tax, driven by the human granzyme B promoter (Tax+), develop osteolytic tumors. To investigate the progression of the bone-invasive malignancies, wild-type, Tax+, and Tax+/interferon-γ-/- mice were assessed using necropsy, histologic examination, IHC analysis, flow cytometry, and advanced imaging. Tax+ and Tax+/interferon-γ-/- malignancies of the ear, tail, and foot comprised poorly differentiated, round to spindle-shaped cells with prominent neutrophilic infiltrates. Tail tumors originated from muscle, nerve, and/or tendon sheaths, with frequent invasion into adjacent bone. F4/80+ and anti-mouse CD11b (Mac-1)+ histiocytic cells predominated within the tumors. Three Tax+/interferon-γ-/- cell lines were generated for in vivo allografts, in vitro gene expression and bone resorption assays. Two cell lines were of monocyte/macrophage origin, and tumors formed in vivo in all three. Differences in Pthrp, Il6, Il1a, Il1b, and Csf3 expression in vitro were correlated with differences in in vivo plasma calcium levels, tumor growth, metastasis, and neutrophilic inflammation. Tax+ mouse tumors were classified as bone-invasive histiocytic sarcomas. The cell lines are ideal for further examination of the role of HTLV-1 Tax in osteolytic tumor formation and the development of hypercalcemia and tumor-associated inflammation.

Human viruses and cancer

The first human tumor virus was discovered in the middle of the last century by Anthony Epstein, Bert Achong and Yvonne Barr in African pediatric patients with Burkitt's lymphoma. To date, seven viruses -EBV, KSHV, high-risk HPV, MCPV, HBV, HCV and HTLV1- have been consistently linked to different types of human cancer, and infections are estimated to account for up to 20% of all cancer cases worldwide. Viral oncogenic mechanisms generally include: generation of genomic instability, increase in the rate of cell proliferation, resistance to apoptosis, alterations in DNA repair mechanisms and cell polarity changes, which often coexist with evasion mechanisms of the antiviral immune response. Viral agents also indirectly contribute to the development of cancer mainly through immunosuppression or chronic inflammation, but also through chronic antigenic stimulation. There is also evidence that viruses can modulate the malignant properties of an established tumor. In the present work, causation criteria for viruses and cancer will be described, as well as the viral agents that comply with these criteria in human tumors, their epidemiological and biological characteristics, the molecular mechanisms by which they induce cellular transformation and their associated cancers.

The MHC-II transactivator CIITA, a restriction factor against oncogenic HTLV-1 and HTLV-2 retroviruses: similarities and differences in the inhibition of Tax-1 and Tax-2 viral transactivators

The activation of CD4(+) T helper cells is strictly dependent on the presentation of antigenic peptides by MHC class II (MHC-II) molecules. MHC-II expression is primarily regulated at the transcriptional level by the AIR-1 gene product CIITA (class II transactivator). Thus, CIITA plays a pivotal role in the triggering of the adaptive immune response against pathogens. Besides this well known function, we recently found that CIITA acts as an endogenous restriction factor against HTLV-1 (human T cell lymphotropic virus type 1) and HTLV-2 oncogenic retroviruses by targeting their viral transactivators Tax-1 and Tax-2, respectively. Here we review our findings on CIITA-mediated inhibition of viral replication and discuss similarities and differences in the molecular mechanisms by which CIITA specifically counteracts the function of Tax-1 and Tax-2 molecules. The dual function of CIITA as a key regulator of adaptive and intrinsic immunity represents a rather unique example of adaptation of host-derived factors against pathogen infections during evolution.

Bcl-3 suppresses Tax-induced NF-κB activation through p65 nuclear translocation blockage in HTLV-1-infected cells

Human T cell leukemia virus type 1 (HTLV-1) Tax-induced persistent activation of the NF-κB pathway is perceived as the primary cause of adult T cell leukemia (ATL), an aggressive leukemia caused by HTLV-1. Although elevated oncoprotein Bcl-3 levels are found in many HTLV-1-infected T cell lines and ATL cells, the role of Bcl-3 in the malignant progression caused by HTLV-1 retrovirus remains poorly understood. We confirmed, in the present study, that the Tax-induced NF-κB activation involves the regulation of Bcl-3. Both knockdown and overexpression of Bcl-3 inhibit the Tax-induced NF-κB activation. Similarly, excessive Bcl-3 inhibits the NF-κB/DNA binding activity and significantly decreases Tax-induced p65 nuclear translocation. The present results demonstrate the pleiotropic roles of Bcl-3 in Tax-induced NF-κB activation and indicate that a balance in the aberrant Bcl-3 expression may be established to play an important role in the maintenance of proliferation and inhibition of apoptosis in HTLV-1-infected and ATL cells.

Animal models on HTLV-1 and related viruses: what did we learn?

Retroviruses are associated with a wide variety of diseases, including immunological, neurological disorders, and different forms of cancer. Among retroviruses, Oncovirinae regroup according to their genetic structure and sequence, several related viruses such as human T-cell lymphotropic viruses types 1 and 2 (HTLV-1 and HTLV-2), simian T cell lymphotropic viruses types 1 and 2 (STLV-1 and STLV-2), and bovine leukemia virus (BLV). As in many diseases, animal models provide a useful tool for the studies of pathogenesis, treatment, and prevention. In the current review, an overview on different animal models used in the study of these viruses will be provided. A specific attention will be given to the HTLV-1 virus which is the causative agent of adult T-cell leukemia/lymphoma (ATL) but also of a number of inflammatory diseases regrouping the HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), infective dermatitis and some lung inflammatory diseases. Among these models, rabbits, monkeys but also rats provide an excellent in vivo tool for early HTLV-1 viral infection and transmission as well as the induced host immune response against the virus. But ideally, mice remain the most efficient method of studying human afflictions. Genetically altered mice including both transgenic and knockout mice, offer important models to test the role of specific viral and host genes in the development of HTLV-1-associated leukemia. The development of different strains of immunodeficient mice strains (SCID, NOD, and NOG SCID mice) provide a useful and rapid tool of humanized and xenografted mice models, to test new drugs and targeted therapy against HTLV-1-associated leukemia, to identify leukemia stem cells candidates but also to study the innate immunity mediated by the virus. All together, these animal models have revolutionized the biology of retroviruses, their manipulation of host genes and more importantly the potential ways to either prevent their infection or to treat their associated diseases.

Pediatric T- and NK-cell lymphomas: new biologic insights and treatment strategies

T- and natural killer (NK)-cell lymphomas are challenging childhood neoplasms. These cancers have varying presentations, vast molecular heterogeneity, and several are quite unusual in the West, creating diagnostic challenges. Over 20 distinct T- and NK-cell neoplasms are recognized by the 2008 World Health Organization classification, demonstrating the diversity and potential complexity of these cases. In pediatric populations, selection of optimal therapy poses an additional quandary, as most of these malignancies have not been studied in large randomized clinical trials. Despite their rarity, exciting molecular discoveries are yielding insights into these clinicopathologic entities, improving the accuracy of our diagnoses of these cancers, and expanding our ability to effectively treat them, including the use of new targeted therapies. Here, we summarize this fascinating group of lymphomas, with particular attention to the three most common subtypes: T-lymphoblastic lymphoma, anaplastic large cell lymphoma, and peripheral T-cell lymphoma-not otherwise specified. We highlight recent findings regarding their molecular etiologies, new biologic markers, and cutting-edge therapeutic strategies applied to this intriguing class of neoplasms.

Human pathogens and the host cell SUMOylation system

Since posttranslational modification (PTM) by the small ubiquitin-related modifiers (SUMOs) was discovered over a decade ago, a huge number of cellular proteins have been found to be reversibly modified, resulting in alteration of differential cellular pathways. Although the molecular consequences of SUMO attachment are difficult to predict, the underlying principle of SUMOylation is altering inter- and/or intramolecular interactions of the modified substrate, changing localization, stability, and/or activity. Unsurprisingly, many different pathogens have evolved to exploit the cellular SUMO modification system due to its functional flexibility and far-reaching functional downstream consequences. Although the extensive knowledge gained so far is impressive, a definitive conclusion about the role of SUMO modification during virus infection in general remains elusive and is still restricted to a few, yet promising concepts. Based on the available data, this review aims, first, to provide a detailed overview of the current state of knowledge and, second, to evaluate the currently known common principles/molecular mechanisms of how human pathogenic microbes, especially viruses and their regulatory proteins, exploit the host cell SUMO modification system.

Move or die: the fate of the Tax oncoprotein of HTLV-1

The HTLV-1 Tax protein both activates viral replication and is involved in HTLV-1-mediated transformation of T lymphocytes. The transforming properties of Tax include altering the expression of select cellular genes via activation of cellular pathways and perturbation of both cell cycle control mechanisms and apoptotic signals. The recent discovery that Tax undergoes a hierarchical sequence of posttranslational modifications that control its intracellular localization provides provocative insights into the mechanisms regulating Tax transcriptional and transforming activities.

Correlation between polymorphisms at interleukin-6 but not at interleukin-10 promoter and the risk of human T lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis in Brazilian individuals

HTLV-1 is the etiologic agent of ATL and HAM/TSP. The majority of HTLV-1-infected individuals remain asymptomatic, indicating that the infection alone is not sufficient to cause the diseases. It has been reported that cytokine gene polymorphisms, including polymorphisms at IL-6 and IL-10 gene, might be important. We analyzed SNP in the promoter region of the IL-6: -174, -572, -597, and -634 positions, and IL-10: -592 position to evaluate the role of these polymorphisms in the HAM/TSP pathogenesis in 133 HTLV-1 infected individuals and in 100 healthy individuals from Salvador, Bahia, Brazil. The -634C allele frequencies were higher among HAM/TSP patients (21.2%) than among oligosymptomatic (6.5%; P = 0.038) and asymptomatic (9.5%; P = 0.025) subjects. Similarly, the -174G allele frequencies were higher in HAM/TSP patients than in oligosymptomatic patients (P = 0.02). Moreover, the -634GC/-174GG genotype combination was identified at a higher frequency (38.5%) in the HAM/TSP patients than in subjects with other clinical status (8.7%; P = 0.016 for oligosymptomatic and 15.5%, P = 0.012 for asymptomatic patients). However, the multivariate logistic regression including the genotypes of the three studied loci showed that only -634 C IL-6 carriers remain as significant and independent TSP/HAM predictor (odds ratio [OR] = 5.31; 95% [CI] = 1.60-17.56; P = 0.006). We suggest that -634 G C in IL-6 could contribute to HAM/TSP development and that identification of the collective influence of several cytokine polymorphisms, their prevalence, and their interaction could help to better understand this disease.

Human T-cell leukemia virus type 1 Tax and cellular transformation

Infection of T-cells by human T-cell leukemia virus type 1 (HTLV-1) causes a lymphoproliferative malignancy known as adult T-cell leukemia (ATL). ATL is characterized by abnormal lymphocytes, called flower cells, which have cleaved and convoluted nuclei. Tax, encoded by the HTLV-1 pX region, is a critical nonstructural protein that plays a central role in leukemogenesis; however, the mechanisms of HTLV-1 oncogenesis have not been clarified fully. In this review, we summarize current thinking on how Tax may affect ATL leukemogenesis.

Tax ubiquitylation and sumoylation control critical cytoplasmic and nuclear steps of NF-κB activation

The Tax oncoprotein plays a crucial role in the proliferation and transformation of human T-cell leukemia virus type I (HTLV-I)–infected T lymphocytes through various mechanisms, including activation of the nuclear factor (NF)–κB pathway. We found that cytoplasmic ubiquitylation of Tax C-terminal lysines is critical for Tax binding to the IkappaB kinase complex and subsequent nuclear translocation of RelA. Conversely, we demonstrate that the same lysines are sumoylated in the nucleus, an event required for the formation of RelA/p300-enriched Tax nuclear bodies and full NF-κB transcriptional activation. In contrast, Tax ubiquitylation and sumoylation are dispensable for its activation of cyclic adenosine monophosphate response element binding protein (CREB)–dependent genes. Thus, ubiquitylation and sumoylation of the same residues of Tax regulate 2 essential steps controlling NF-κB activation, demonstrating how these posttranslational modifications can cooperate to promote Tax-induced transformation.

Foxp3 represses retroviral transcription by targeting both NF-kappaB and CREB pathways

Forkhead box (Fox)/winged-helix transcription factors regulate multiple aspects of immune responsiveness and Foxp3 is recognized as an essential functional marker of regulatory T cells. Herein we describe downstream signaling pathways targeted by Foxp3 that may negatively impact retroviral pathogenesis. Overexpression of Foxp3 in HEK 293T and purified CD4+ T cells resulted in a dose-dependent and time-dependent decrease in basal levels of nuclear factor-kappaB (NF-kappaB) activation. Deletion of the carboxyl-terminal forkhead (FKH) domain, critical for nuclear localization and DNA-binding activity, abrogated the ability of Foxp3 to suppress NF-kappaB activity in HEK 293T cells, but not in Jurkat or primary human CD4+ T cells. We further demonstrate that Foxp3 suppressed the transcription of two human retroviral promoters (HIV-1 and human T cell lymphotropic virus type I [HTLV-I]) utilizing NF-kappaB-dependent and NF-kappaB-independent mechanisms. Examination of the latter identified the cAMP-responsive element binding protein (CREB) pathway as a target of Foxp3. Finally, comparison of the percent Foxp3+CD4+CD25+ T cells to the HTLV-I proviral load in HTLV-I-infected asymptomatic carriers and patients with HTLV-I-associated myelopathy/tropical spastic paraparesis suggested that high Foxp3 expression is associated with low proviral load and absence of disease. These results suggest an expanded role for Foxp3 in regulating NF-kappaB- and CREB-dependent cellular and viral gene expression.

Human T-cell leukemia virus type 1 expressing nonoverlapping tax and rex genes replicates and immortalizes primary human T lymphocytes but fails to replicate and persist in vivo

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus associated primarily with adult T-cell leukemia and neurological disease. HTLV-1 encodes the positive trans-regulatory proteins Tax and Rex, both of which are essential for viral replication. Tax activates transcription initiation from the viral long terminal repeat and modulates the transcription or activity of a number of cellular genes. Rex regulates gene expression posttranscriptionally by facilitating the cytoplasmic expression of incompletely spliced viral mRNAs. Tax and Rex mutants have been identified that have defective activities or impaired biochemical properties associated with their function. To ultimately determine the contribution of specific protein activities on viral replication and cellular transformation of primary T cells, mutants need to be characterized in the context of an infectious molecular clone. Since the tax and rex genes are in partially overlapping reading frames, mutation in one gene frequently disrupts the other, confounding interpretation of mutational analyses in the context of the virus. Here we generated and characterized a unique proviral clone (H1IT) in which the tax and rex genes were separated by expressing Tax from an internal ribosome entry site. We showed that H1IT expresses both functional Tax and Rex. In short- and long-term coculture assays, H1IT was competent to infect and immortalize primary human T cells similar to wild-type HTLV-1. In contrast, H1IT failed to efficiently replicate and persist in inoculated rabbits, thus emphasizing the importance of temporal and quantitative regulation of specific mRNA for viral survival in vivo.

Transcriptional regulation of parathyroid hormone-related protein promoter P3 by ETS-1 in adult T-cell leukemia/lymphoma

Parathyroid hormone-related protein (PTHrP) plays a primary role in the development of humoral hypercalcemia of malignancy seen in the majority of adult T-cell leukemia/lymphoma (ATLL) patients with human T-cell lymphotropic virus type-1 (HTLV-1) infection. HTLV-1 Tax has been shown to complex with ETS-1 and SP1 to transactivate the PTHrP P3 promoter. Previously, we established a SCID/bg mouse model of human ATL with RV-ATL cells and showed that PTHrP expression was independent of Tax. In this study, we report an inverse correlation of PTHrP with tax/rex mRNA in multiple HTLV-1-positive cell lines and RV-ATL cells. Stimulation of Jurkat T cells with PMA/ionomycin upregulated the PTHrP P3 promoter by a previously characterized Ets binding site and also induced protein/DNA complex formation identical to that observed in RV-ATL cells. Further, we provide evidence that cotransfection with Ets-1 and constitutively active Mek-1 in HTLV-1-negative transformed T cells with stimulation by PMA/ionomycin not only resulted in a robust induction of PTHrP P3 but also formed a complex with ETS-1/P3 EBS similar to that in ATLL cells. Our data demonstrate that transcriptional regulation of PTHrP in ATLL cells can be controlled by T-cell receptor signaling and the ETS and MAPK ERK pathway in a Tax-independent manner.

Activation of human T cell leukemia virus type 1 LTR promoter and cellular promoter elements by T cell receptor signaling and HTLV-1 Tax expression

Human T cell leukemia virus 1 (HTLV-1) gene expression is regulated by both the viral Tax protein and by cellular transcriptional factors. We have previously shown that immune activation stimuli such as phorbol esters (PMA) and phytohemagglutinin (PHA) cooperate with HTLV-1 Tax expression to enhance HTLV-1 gene expression in infected T cells through increased activity of the HTLV-1 LTR. We now extend these studies to demonstrate roles for the T cell receptor complex, Lck, and Ras molecules in the coactivation of the HTLV-1 LTR by Tax and T cell activation stimuli. We also observe coactivation of Tax-responsive cellular promoter elements containing NF-kappaB and serum response factor (SRF) binding sites by Tax and T cell activation stimuli. These results suggest a model whereby T cell receptor stimulation and Tax expression coactivate HTLV-1 gene expression and cellular gene expression, enhancing activation of latent HTLV-1 and expression of cellular genes involved in disease pathogenesis.

Cell transformation by Herpesvirus saimiri

Herpesvirus saimiri (Saimiriine herpesvirus-2), a gamma2-herpesvirus (rhadinovirus) of non-human primates, causes T-lymphoproliferative diseases in susceptible organisms and transforms human and non-human T lymphocytes to continuous growth in vitro in the absence of stimulation. T cells transformed by H. saimiri retain many characteristics of intact T lymphocytes, such as the sensitivity to interleukin-2 and the ability to recognize the corresponding antigens. As a result, H. saimiri is widely used in immunobiology for immortalization of various difficult-to-obtain and/or -to-maintain T cells in order to obtain useful experimental models. In particular, H. saimiri-transformed human T cells are highly susceptible to infection with HIV-1 and -2. This makes them a convenient tool for propagation of poorly replicating strains of HIV, including primary clinical isolates. Therefore, the mechanisms mediating transformation of T cells by H. saimiri are of considerable interest. A single transformation-associated protein, StpA or StpB, mediates cell transformation by H. saimiri strains of group A or B, respectively. Strains of group C, which exhibit the highest oncogenic potential, have two proteins involved in transformation-StpC and Tip. Both proteins have been shown to dramatically affect signal transduction pathways leading to the activation of crucial transcription factors. This review is focused on the biological effects and molecular mechanisms of action of proteins involved in H. saimiri-dependent transformation.

Activation of simian virus 40 promoter by HTLV-I Tax protein: role of NF-κB and CBP

HTLV-I is implicated with adult T-cell leukemia and certain other clinical disorders. The viral Tax protein is regarded as a key element in HTLV-I pathogenicity due to its ability to activate a wide variety of cellular regulatory factors. As such, Tax may likely activate also latent infection of certain other pathogenic viruses whose expression is modulated by cellular transcription factors. Therefore, investigation of Tax effect on the expression of these viruses is of particular clinical importance, since HTLV-I infection of carriers harboring such latent viruses may trigger their related diseases. In this study we focused on simian virus 40 and demonstrated that Tax activates the promoter of this virus through NF-kappaB-associated pathway. Furthermore, we show that this activation requires an interaction of the NF-kappaB factor p65(RelA) with CBP, which depends on PKA-mediated phosphorylation of p65(RelA). Finally, the present study proves that the nuclear Tax plays a critical role in Tax-induced NF-kappaB-mediated SV40 activation.

Transformation studies with a human T-cell leukemia virus type 1 molecular clone

In in vitro studies human T-cell leukemia virus type 1 (HTLV-1) may be produced by stable or transient transfection of target cells with an infectious molecular clone. Studies using primary human T cells, the natural targets of HTLV-1 infection, are hampered by difficulty in achieving significant infection with cell-free virus and a poor efficiency of transfection of primary cells. A method is described for the generation of stable cell lines expressing HTLV-1 from an infectious proviral clone. The stably transfected cells can be irradiated and cocultured with human peripheral blood mononuclear cells (PBMC) resulting in infected primary cells. These cells become immortalized, IL-2 dependent lines, which contain integrated copies of provirus and express a full spectrum of viral proteins. Analysis of cellular markers indicates that immortalized cell lines consist of CD3+/CD4+ T cells, matching the most common adult T-cell leukemia (ATL) cell phenotype. The method described has great utility in the study of the replication and transformation capacity of HTLV and HTLV mutant viruses in their natural targets, primary human T lymphocytes.

Molecular mechanisms of the effect of herpesvirus saimiri protein StpC on the signaling pathway leading to NF-kappaB activation

Herpesvirus saimiri (Saimiriine herpesvirus-2) causes lethal T lymphoproliferative diseases in the susceptible species and transforms T lymphocytes to continuous growth in vitro. H. saimiri-induced transformation of T cells is becoming an important experimental tool of biomedical research. Two proteins of H. saimiri subgroup C, Tip and StpC, are essential for T cell transformation by this virus. It has been shown previously that StpC transforms fibroblasts, activates NF-kappaB, and binds to tumor necrosis factor (TNF)-receptor-associated factor (TRAF) proteins, but the molecular mechanism of its action remains insufficiently understood. This study further characterized the effect of StpC on NF-kappaB. First, StpC activates NF-kappaB via the consensus pathway involving activation of I-kappaB kinase and subsequent phosphorylation and degradation of I-kappaB in both T lymphoid and epithelial cells. Second, triggering of this pathway by StpC in both T lymphoid and epithelial cells is dependent on the presence of functional NF-kappaB-inducing kinase (NIK). Third, StpC physically interacts with TRAF in epithelial cells, and the effect of StpC on NF-kappaB activity in these cells requires the presence of functional TRAF. Finally the effect of StpC is completely independent of TNF-alpha, a well described stimulus of NF-kappaB activity. Moreover it appears that StpC uncouples stimulation of NF-kappaB activity from TNF-alpha stimulation. Overall these results argue that the effect of StpC on NF-kappaB is similar to the effects of other viral proteins, "usurping" the TRAF/NIK/I-kappaB kinase pathway, and reinforce the notion that the role of StpC in cell transformation by H. saimiri may be mediated by signaling that results in NF-kappaB activation.

Overexpression of MEKK3 confers resistance to apoptosis through activation of NFkappaB

Many cancers have constitutively activated NFkappaB, the elevation of which contributes to cancer cell resistance to chemotherapeutic agent-induced apoptosis. Although mitogen-activated protein kinase/extracellular-regulated kinase kinase kinase-3 (MEKK3) has been shown to participate in the activation of NFkappaB, its relations to apoptosis and cancer are unclear. In this study, we established cell model systems to examine whether stable expression of MEKK3 could lead to increased NFkappaB activity and confer resistance to apoptosis. In addition, we investigated in breast and ovarian cancers whether MEKK3 expression may be altered and correlated with aberrant NFkappaB activity. We show that stable cell lines overexpressing MEKK3 not only had elevated levels of NFkappaB binding activity but also were more responsive to cytokine stimulation. These stable cells showed 2-4-fold higher basal expression of Bcl-2 and xIAP than the parental cells. Consistent with this increased expression of cell survival genes, MEKK3 stable cells showed reduced activation of caspases 3 and 8 and poly(ADP-ribose) polymerase cleavage and dramatically increased resistance to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand, doxorubicin, daunorubicin, camptothecin, and paclitaxel. Intriguingly, analysis of human breast and ovarian cancers showed that a significant fraction of these samples have elevated MEKK3 protein levels with corresponding increases in NFkappaB binding activities. Thus, our results established that elevated expression of MEKK3 appears to be a frequent occurrence in breast and ovarian cancers and that overexpression of MEKK3 in cells leads to increased NFkappaB activity and increased expression of cell survival factors and ultimately contributes to their resistance to apoptosis. As such, MEKK3 may serve as a therapeutic target to control cancer cell resistance to cytokine- or drug-induced apoptosis.

Protection of islets by in situ peptide-mediated transduction of the Ikappa B kinase inhibitor Nemo-binding domain peptide

We have previously demonstrated that adenoviral gene transfer of the NF-kappaB inhibitor IkappaB to human islets results in protection from interleukin (IL)-1beta-mediated dysfunction and apoptosis. Here we report that human and mouse islets can be efficiently transduced by a cationic peptide transduction domain (PTD-5) without impairment of islet function. PTD mediated delivery of a peptide inhibitor of the IL-1beta-induced IkappaB kinase (IKK), derived from IKKbeta (NBD; Nemo-binding domain), and completely blocked the detrimental effects of IL-1beta on islet function and NF-kappaB activity, in a similar manner to Ad-IkappaB. We also demonstrate that mouse islets can be transduced in situ by infusion of the transduction peptide through the bile duct prior to isolation, resulting in 40% peptide transduction of the beta-cells. Delivery of the IKK inhibitor transduction fusion peptide (PTD-5-NBD) in situ to mouse islets resulted in improved islet function and viability after isolation. These results demonstrate the feasibility of using PTD-mediated delivery to transiently modify islets in situ to improve their viability and function during isolation, prior to transplantation.

Critical role of human T-lymphotropic virus type 1 accessory proteins in viral replication and pathogenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) infection is associated with a diverse range of lymphoproliferative and neurodegenerative diseases, yet pathogenic mechanisms induced by the virus remain obscure. This complex retrovirus contains typical structural and enzymatic genes but also unique regulatory and accessory genes in four open reading frames (ORFs) of the pX region of the viral genome (pX ORFs I to IV). The regulatory proteins encoded by pX ORFs III and IV, Tax and Rex, respectively, have been extensively characterized. In contrast the contribution of the four accessory proteins p12(I), p27(I), p13(II), and p30(II), encoded by pX ORFs I and II, to viral replication and pathogenesis remained unclear. Proviral clones that are mutated in either pX ORF I or II, while fully competent in cell culture, are severely limited in their replicative capacity in a rabbit model. Emerging evidence indicates that the HTLV-1 accessory proteins are critical for establishment of viral infectivity, enhance T-lymphocyte activation, and potentially alter gene transcription and mitochondrial function. HTLV-1 pX ORF I expression is critical to the viral infectivity in resting primary lymphocytes, suggesting a role for p12(I) in lymphocyte activation. The endoplasmic reticulum and cis-Golgi localizing p12(I), encoded from pX ORF I, activates NFAT, a key T-cell transcription factor, through calcium-mediated signaling pathways and may lower the threshold of lymphocyte activation via the JAK/STAT pathway. In contrast p30(II) localizes to the nucleus and represses viral promoter activity, but may regulate cellular gene expression through p300/CBP or related coactivators of transcription. p13(II) targets mitochondrial proteins, where it alters the organelle morphology and may influence energy metabolism. Collectively, studies of the molecular functions of the HTLV-1 accessory proteins provide insight into strategies used by retroviruses that are associated with lymphoproliferative diseases.

Elevated NF-kappaB activation in nonobese diabetic mouse dendritic cells results in enhanced APC function

We have recently demonstrated that dendritic cells (DC) prepared from nonobese diabetic (NOD) mice, a spontaneous model for insulin-dependent diabetes mellitus, exhibit elevated levels of NF-kappaB activation upon stimulation. In the current study, we investigated the influence of dysregulation of NF-kappaB activation on the APC function of bone marrow-derived DC prepared from NOD vs BALB/c and nonobese diabetes-resistant mice. NOD DC pulsed with either peptide or virus were found to be more efficient than BALB/c DC at stimulating in vitro naive Ag-specific CD8+ T cells. The T cell stimulatory capacity of NOD DC was suppressed by gene transfer of a modified form of IkappaBalpha, indicating a direct role for NF-kappaB in this process. Furthermore, neutralization of IL-12(p70) to block autocrine-mediated activation of DC also significantly reduced the capacity of NOD DC to stimulate T cells. Despite a reduction in low molecular mass polypeptide-2 expression relative to BALB/c DC, no effect on proteasome-dependent events associated with the NF-kappaB signaling pathway or Ag processing was detected in NOD DC. Finally, DC from nonobese diabetes-resistant mice, a strain genotypically similar to NOD yet disease resistant, resembled BALB/c and not NOD DC in terms of the level of NF-kappaB activation, secretion of IL-12(p70) and TNF-alpha, and the capacity to stimulate T cells. Therefore, elevated NF-kappaB activation and enhanced APC function are specific for the NOD genotype and correlate with the progression of insulin-dependent diabetes mellitus. These results also provide further evidence indicating a key role for NF-kappaB in regulating the APC function of DC.

Activation of HIV in human skin by ultraviolet B radiation and its inhibition by NFkappaB blocking agents

To determine whether ultraviolet B (UVB) irradiation leads to activation of HIV in human skin, we conducted prospective and controlled studies in two academic medical centers in Texas from July 1995 to April 1999. HIV-positive patients with UV-treatable skin diseases were enrolled at each center, 18 subjects at one and 16 at the other. In one center, specimens from lesional and nonlesional skin biopsies were taken before and after sham- or UVB-irradiation administered in vivo or in vitro. In the other center, UVB phototherapy was administered three times weekly and specimens from skin biopsies were taken before and after 2 weeks (six treatments). Cutaneous HIV load was assessed using reverse transcriptase-polymerase chain reaction and reverse transcriptase-polymerase chain reaction in situ hybridization. UVB irradiation led to a 6-10-fold increase in the number of HIV in skin. To ascertain a role for nuclear factor kappa B (NFkappaB) in UVB-inducible HIV activation, two types of blockers, NFkappaB oligonucleotide decoy and sodium salicylate, were tested; each inhibited UVB-inducible HIV activation in skin partially. We conclude that UVB irradiation leads to increased numbers of HIV in human skin via processes that include release of cytoplasmic NFkappaB.

IKKgamma /NEMO facilitates the recruitment of the IkappaB proteins into the IkappaB kinase complex

IKKgamma/NEMO is an essential regulatory component of the IkappaB kinase complex that is required for NF-kappaB activation in response to various stimuli including tumor necrosis factor-alpha and interleukin-1beta. To investigate the mechanism by which IKKgamma/NEMO regulates the IKK complex, we examined the ability of IKKgamma/NEMO to recruit the IkappaB proteins into this complex. IKKgamma/NEMO binding to wild-type, but not to a kinase-deficient IKKbeta protein, facilitated the association of IkappaBalpha and IkappaBbeta with the high molecular weight IKK complex. Following tumor necrosis factor-alpha treatment of HeLa cells, the majority of the phosphorylated form of endogenous IkappaBalpha was associated with the high molecular weight IKK complex in HeLa cells and parental mouse embryo fibroblasts but not in IKKgamma/NEMO-deficient cells. Finally, we demonstrate that IKKgamma/NEMO facilitates the association of the IkappaB proteins and IKKbeta and leads to increases in IKKbeta kinase activity. These results suggest that an important function of IKKgamma/NEMO is to facilitate the association of both IKKbeta and IkappaB in the high molecular weight IKK complex to increase IkappaB phosphorylation.

Role of IKKgamma/nemo in assembly of the Ikappa B kinase complex

IKKgamma/NEMO is a protein that is critical for the assembly of the high molecular weight IkappaB kinase (IKK) complex. To investigate the role of IKKgamma/NEMO in the assembly of the IKK complex, we conducted a series of experiments in which the chromatographic distribution of extracts prepared from cells transiently expressing epitope-tagged IKKgamma/NEMO and the IKKs were examined. When expressed alone following transfection, IKKalpha and IKKbeta were present in low molecular weight complexes migrating between 200 and 400 kDa. However, when coexpressed with IKKgamma/NEMO, both IKKalpha and IKKbeta migrated at approximately 600 kDa which was similar to the previously described IKK complex that is activated by cytokines such as tumor necrosis factor-alpha. When either IKKalpha or IKKbeta was expressed alone with IKKgamma/NEMO, IKKbeta but not IKKalpha migrated in the higher molecular weight IKK complex. Constitutively active or inactive forms of IKKbeta were both incorporated into the high molecular weight IKK complex in the presence of IKKgamma/NEMO. The amino-terminal region of IKKgamma/NEMO, which interacts directly with IKKbeta, was required for formation of the high molecular weight IKK complex and for stimulation of IKKbeta kinase activity. These results suggest that recruitment of the IKKs into a high molecular complex by IKKgamma/NEMO is a crucial step involved in IKK function.