A cooperative interaction of human T-cell leukemia virus type 1 Tax with the p21 cyclin-dependent kinase inhibitor activates the human immunodeficiency virus type 1 enhancer

Specific pathogen free macaque colonies: a review of principles and recent advances for viral testing and colony management

Specific pathogen free (SPF) macaques provide valuable animal models for biomedical research. In 1989, the National Center for Research Resources [now Office of Research Infrastructure Programs (ORIP)] of the National Institutes of Health initiated experimental research contracts to establish and maintain SPF colonies. The derivation and maintenance of SPF macaque colonies is a complex undertaking requiring knowledge of the biology of the agents for exclusion and normal physiology and behavior of macaques, application of the latest diagnostic technology, facilitiy management, and animal husbandry. This review provides information on the biology of the four viral agents targeted for exclusion in ORIP SPF macaque colonies, describes current state-of-the-art viral diagnostic algorithms, presents data from proficiency testing of diagnostic assays between laboratories at institutions participating in the ORIP SPF program, and outlines management strategies for maintaining the integrity of SPF colonies using results of diagnostic testing as a guide to decision making.

Vpr and its interactions with cellular proteins

Like most viral regulatory proteins, HIV-1 Vpr and homologous proteins from primate lentiviruses are small and multifunctional. They are associated with a plethora of effects and functions, including induction of cell cycle arrest in the G(2) phase, induction of apoptosis, transactivation, enhancement of the fidelity of reverse transcription, and nuclear import of viral DNA in macrophages and other nondividing cells. This review focuses on the cellular proteins that have been reported to interact with Vpr and their significance with respect to the known functions and effects of Vpr on cells and on viral replication.

Two specific drugs, BMS-345541 and purvalanol A induce apoptosis of HTLV-1 infected cells through inhibition of the NF-kappaB and cell cycle pathways

Human T-cell leukemia virus type-1 (HTLV-1) induces adult T-cell leukemia/lymphoma (ATL/L), a fatal lymphoproliferative disorder, and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic progressive disease of the central nervous system after a long period of latent infection. Although the mechanism of transformation and leukemogenesis is not fully elucidated, there is evidence to suggest that the viral oncoprotein Tax plays a crucial role in these processes through the regulation of several pathways including NF-κB and the cell cycle pathways. The observation that NF-κB, which is strongly induced by Tax, is indispensable for the maintenance of the malignant phenotype of HTLV-1 by regulating the expression of various genes involved in cell cycle regulation and inhibition of apoptosis provides a possible molecular target for these infected cells. To develop potential new therapeutic strategies for HTLV-1 infected cells, in this present study, we initially screened a battery of NF-κB and CDK inhibitors (total of 35 compounds) to examine their effects on the growth and survival of infected T-cell lines. Two drugs namely BMS-345541 and Purvalanol A exhibited higher levels of growth inhibition and apoptosis in infected cell as compared to uninfected cells. BMS-345541 inhibited IKKβ kinase activity from HTLV-1 infected cells with an IC₅₀ (the 50% of inhibitory concentration) value of 50 nM compared to 500 nM from control cells as measured by in vitro kinase assays. The effects of Purvalanol A were associated with suppression of CDK2/cyclin E complex activity as previously shown by us. Combination of both BMS-345541 and Purvalanol A showed a reduced level of HTLV-1 p19 Gag production in cell culture. The apparent apoptosis in these infected cells were associated with increased caspase-3 activity and PARP cleavage. The potent and selective apoptotic effects of these drugs suggest that both BMS-345541 and Purvalanol A, which target both NF-κB and CDK complex and the G1/S border, might be promising new agents in the treatment of these infected patients.

Effect of HIV-1 Vpr on cell cycle regulators

Cell cycle is one of the most complex processes in the life of a dividing cell. It involves numerous regulatory proteins, which direct the cell through a specific sequence of events for the production of two daughter cells. Cyclin-dependent kinases (cdks), which complex with the cyclin proteins, are the main players in the cell cycle. They can regulate the progression of the cells through different stages regulated by several proteins including p53, p21(WAF1), p19, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRB and E2F. A cell cycle can be altered to the advantage of many viral agents, most notably polyomaviruses, papillomaviruses, adenoviruses, and retroviruses. In addition, viral protein R (Vpr) is a protein encoded by the human immunodeficiency virus type 1 (HIV-1). HIV-1, the causative agent of acquired immunodeficiency syndrome (AIDS), is a member of the lentivirus class of retroviruses. This accessory protein plays an important role in the regulation of the cell cycle by causing G(2) arrest and affecting cell cycle regulators. Vpr prevents infected cells from proliferating, and collaborates with the matrix protein (MA) to enable HIV-1 to enter the nucleus of nondividing cells. Studies from different labs including ours showed that Vpr affects the functions of cell cycle proteins, including p53 and p21(WAF1). Thus, the replication of HIV-1, and ultimately its pathogenesis, are intrinsically tied to cell-cycle control.

p21(Waf1/Cip1/Sdi1) prevents apoptosis as well as stimulates growth in cells transformed or immortalized by human T-cell leukemia virus type 1-encoded tax

Human T-cell leukemia virus type 1 (HTLV-1) Tax regulates the expression of virally encoded genes, as well as various endogenous host genes in trans. Tax-mediated regulation of gene expression is important for the immortalization of normal human T lymphocytes and the transformation of fibroblast cells, such as Rat-1 cells. Tax has the ability to transactivate p21(Waf1/Cip1/Sdi1), resulting in high expression levels in HTLV-1-immortalized cells. Since p21 expression is suppressed due to methylation of the promoter region in Rat-l cell line, p21 may not be critical for the transformation of this cell line by Tax. To further understand the role of p21 for the proliferation of Tax-transformed Rat-1 cells, we examined the effect of ectopic expression of p21 in these cells. Here, we observed that p21 expression enhanced the transformation of this cell line via at least two mechanisms: (i) the enhancement of NF-kappaB activation and/or CREB signaling and (ii) the excitation of antiapoptotic machinery. To analyze the role of p21 that is overexpressed in HTLV-1-immortalized lymphocytes, p21 expression was suppressed by using an antisense oligonucleotide specific for p21 mRNA; these cells then became sensitive to apoptotic induction. These results suggest that p21 plays an important role in the proliferation of Tax-expressing cells through the regulation of at least two independent mechanisms.

Role of tumor suppressor genes in the development of adult T cell leukemia/lymphoma (ATLL)

Adult T cell leukemia/lymphoma (ATLL) is one of the peripheral T cell malignant neoplasms strongly associated with human T cell leukemia virus type-I (HTLV-I). Although the viral transactivating protein Tax has been proposed to play a critical role in leukemogeneis as shown by its transforming activity in various experimental systems, additional cellular events are required for the development of ATLL. One of the genetic events in ATLL is inactivation of tumor suppressor genes. Among many candidates for tumor suppressor genes, the main genetic events have been reported to center around the cyclin-dependent kinase inhibitors ((CDKIs) p15INK4A, p16INK4B, p18INK4C, p19INK4D, p21WAF1, p27KIP1, and p57KIP2), p53 and Rb genes; all of them play a major regulatory role during G1 to S transition in the cell cycle. Acute/lymphomatous ATLL has frequent alterations of p15 (20%) and p16 (28-67%), while chronic/smoldering ATLL has fewer abnormalities of p15 (0-13%) and p16 (5-26%). Most of these changes are deletion of the genes; fewer samples have mutations. ATLL patients with deleted p15 and/or p16 genes have significantly shorter survival than those individuals with both genes preserved. Although genetic alterations of p18, p19, p21, p27 have rarely been reported, inactivation of these genes may contribute to the development of ATLL because low expression levels of these genes seem to mark ATLL. The p53 gene is mutated in 10-50% of acute/lymphomatous ATLL. Functional impairment of the p53 protein, even if the gene has wild-type sequences, has been suggested in HTLV-I infected cells. Each of these genetic events are mainly found in acute/lymphomatous ATLL, suggesting that alterations of these genes may be associated with transformation to an aggressive phenotype. The Rb tumor suppressor gene is infrequently structurally altered, but one half of ATLL cases have lost expression of this key protein. Notably, alterations of one of the CDKIs, p53 and Rb genes appear to obviate the need for inactivation of other genes in the same pathway. A novel tumor suppressor gene on chromosome 6q may also have a critical role in the pathogenesis of ATLL. Taken together, tumor suppressor genes are frequently altered in acute/lymphomatous ATLL and their alteration is probably the driving force fueling the transition from chronic/smoldering to acute/lymphomatous ATLL.

Effects of histone acetylation and DNA methylation on p21( WAF1) regulation

Cell cycle progression is regulated by interactions between cyclins and cyclin-dependent kinases (CDKs). p21(WAF1) is one of the CIP/KIP family which inhibits CDKs activity. Increased expression of p21(WAF1) may play an important role in the growth arrest induced in transformed cells. Although the stability of the p21( WAF1) mRNA could be altered by different signals, cell differentiation and numerous influencing factors. However, recent studies suggest that two known mechanisms of epigenesis, i.e.gene inactivation by methylation in promoter region and changes to an inactive chromatin by histone deacetylation, seem to be the best candidate mechanisms for inactivation of p21( WAF1). To date, almost no coding region p21(WAF1) mutations have been found in tumor cells, despite extensive screening of hundreds of various tumors. Hypermethylation of the p21(WAF1) promoter region may represent an alternative mechanism by which the p21(WAF1/CIP1) gene can be inactivated. The reduction of cellular DNMT protein levels also induces a corresponding rapid increase in the cell cycle regulator p21(WAF1) protein demonstrating a regulatory link between DNMT and p21(WAF1) which is independent of methylation of DNA. Both histone hyperacetylation and hypoacetylation appear to be important in the carcinoma process, and induction of the p21(WAF1) gene by histone hyperacetylation may be a mechanism by which dietary fiber prevents carcinogenesis. Here, we review the influence of histone acetylation and DNA methylation on p21(WAF1) transcription, and affection of pathways or factors associated such as p 53, E2A, Sp1 as well as several histone deacetylation inhibitors.

Marek's disease herpesvirus transforming protein MEQ: a c-Jun analogue with an alternative life style

In order to adapt to and to cope with an often hostile host environment, many viruses have evolved to encode products that are homologous to cellular proteins. These proteins exploit the existing host machinery and allow viruses to readily integrate into the host functional network. As a result, viruses are able to maneuver their journey seemingly effortlessly inside the host cell to achieve ultimate survival. Such molecular mimicries sometime go overboard, allowing viruses to overtake the cellular pathways or evade the immune system as do many of the retroviral oncogenes. Retroviral oncogenes are derived directly from host genes, and they are virtually identical to host genes in sequences except those mutations that make them unregulatable by host. Oncogenic herpesviruses also encode oncogenes, or transforming genes, which have independently evolved and are distantly related to host genes. However, these genes do share consensus structural motifs with cellular genes involved in cell growth and apoptosis and are functional analogues to host genes. The Marek's disease virus oncoprotein, MEQ, is one such example. MEQ is a basic region-leucine zipper (bZIP) transactivator which shares extensive homology with the Jun/Fos family of transcription factors within the bZIP domain, but not in other regions. Like all other bZIP proteins, MEQ is capable of dimerizing with itself and with a variety of bZIP partners including c-Jun, B-Jun, c-Fos, CREB, ATF-1, ATF-2, and SNF. MEQ-Jun heterodimers bind to a TRE/CRE-like sequence in the meq promoter region and have been shown to up-regulate MEQ expression in both chicken embryo fibroblasts and F9 cells. In addition, the bZIP and transactivation domains are interchangeable between MEQ and c-Jun in terms of transforming potential; i.e. MEQ can functionally substitute for c-Jun. These properties enable MEQ to engage in host cell processes by disguising itself as c-Jun. On the other hand, there are properties of MEQ notably different from c-Jun, which include its capability to bind RNA, to bind a CACAC-bent DNA structure as a homodimer, to inhibit apoptosis, and to interact with CDK2. MEQ's subcellular localization in the nucleolus and coiled body, is also different from Jun/Fos family of transactivators. These unique features may provide the MEQ with additional facility in regulating MDV replication, establishing latency, and cellular transformation. In this review, we will attempt to summarize the past research progress on MDV meq, with a focused on the similarities and differences between MEQ and cellular proteins, and between MEQ and other viral oncoproteins.

HTLV-II down-regulates HIV-1 replication in IL-2–stimulated primary PBMC of coinfected individuals through expression of MIP-1α

The influence of human T-cell leukemia/lymphoma virus type II (HTLV-II) in individuals also infected with HIV-1 is poorly understood. To evaluate the reciprocal influence of HTLV-II and HIV-1 infection, primary peripheral blood mononuclear cell (PBMC) cultures from coinfected individuals were established in the presence of interleukin 2 (IL-2). In these cultures, the kinetics of HTLV-II replication always preceded those of HIV-1. Noteworthy, the kinetics of HIV-1 production were inversely correlated to the HTLV-II proviral load in vivo and its replication ex vivo. These observations suggested a potential interaction between the 2 retroviruses. In this regard, the levels of IL-2, IL-6, and tumor necrosis factor- (TNF-) were measured in the same coinfected PBMC cultures. Endogenous IL-2 was not produced, whereas IL-6 and TNF- were secreted at levels compatible with their known ability to up-regulate HIV-1 expression. The HIV-suppressive CC-chemokines RANTES, macrophage inflammatory protein-1 (MIP-1), and MIP-1β were also determined in IL-2–stimulated PBMC cultures. Of interest, their kinetics and concentrations were inversely related to those of HIV-1 replication. Experiments were performed in which CD8+ T cells or PBMCs from HTLV-II monoinfected individuals were cocultivated with CD4+ T cells from HIV-1 monoinfected individuals separated by a semipermeable membrane in the presence or absence of antichemokine neutralizing antibodies. The results indicate that HTLV-II can interfere with the replicative potential of HIV-1 by up-regulating viral suppressive CC-chemokines and, in particular, MIP-1. This study is the first report indicating that HTLV-II can influence HIV replication, at least in vitro, via up-regulation of HIV-suppressive chemokines.

Functional interactions between herpesvirus oncoprotein MEQ and cell cycle regulator CDK2

Marek's disease virus, an avian alphaherpesvirus, has been used as an excellent model to study herpesvirus oncogenesis. One of its potential oncogenes, MEQ, has been demonstrated to transform a rodent fibroblast cell line, Rat-2, in vitro by inducing morphological transformation and anchorage- and serum-independent growth and by protecting cells from apoptosis induced by tumor necrosis factor alpha, C2-ceramide, UV irradiation, or serum deprivation. In this report, we show that there is a cell cycle-dependent colocalization of MEQ protein and cyclin-dependent kinase 2 (CDK2) in coiled bodies and the nucleolar periphery during the G1/S boundary and early S phase. To our knowledge, this is the first demonstration that CDK2 is found to localize to coiled bodies. Such an in vivo association and possibly subsequent phosphorylation may result in the cytoplasmic translocation of MEQ protein. Indeed, MEQ is expressed in both the nucleus and the cytoplasm during the G1/S boundary and early S phase. In addition, we were able to show in vitro phosphorylation of MEQ by CDKs. We have mapped the CDK phosphorylation site of MEQ to be serine 42, a residue in the proximity of the bZIP domain. An indirect-immunofluorescence study of the MEQ S42D mutant, in which the CDK phosphorylation site was mutated to a charged residue, reveals more prominent cytoplasmic localization. This lends further support to the notion that the translocation of MEQ is regulated by phosphorylation. Furthermore, phosphorylation of MEQ by CDKs drastically reduces the DNA binding activity of MEQ, which may in part account for the lack of retention of MEQ oncoprotein in the nucleus. Interestingly, the localization of CDK2 in coiled bodies and the nucleolar periphery is observed only in MEQ-transformed Rat-2 cells, implicating MEQ in modifying the subcellular localization of CDK2. Taken together, our data suggest that there is a novel reciprocal modulation between the herpesvirus oncoprotein MEQ and CDK2.

Interaction of human immunodeficiency virus type 1 Tat with the transcriptional coactivators p300 and CREB binding protein

Human immunodeficiency virus type 1 (HIV-1) encodes the transactivator protein Tat, which is essential for viral replication and progression to disease. Here we demonstrate that transcriptional activation by HIV-1 Tat involves p300 or the related cellular transcriptional coactivator CREB binding protein (CBP). Tat transactivation was inhibited by the 12S form of the adenovirus E1A gene product, which inhibits p300 function, and this inhibition was independent of its effect on NF-kappaB transcription. A biochemical interaction of p300 with Tat was demonstrated in vitro and in vivo by coimmunoprecipitation. The carboxy-terminal region of p300, which binds to E1A, was shown to bind specifically to the highly conserved basic domain of Tat, which also mediates binding to the Tat-responsive region RNA stem-loop structure. The ability of Tat to interact physically and functionally with this coactivator provides a mechanism to assemble a basal transcription complex which may subsequently respond to the effect of Tat on transcriptional elongation and represents a novel interaction between an RNA binding protein and a transcriptional coactivator.