Search

The expression of BTB-ZF transcription factors such as ThPOK in CD4 + T cells, Bcl6 in T follicular helper cells, and PLZF in natural killer T cells defines the fundamental nature and characteristics of these cells. Screening for lineage-defining BTB-ZF genes led to the discovery of a subset of T cells that expressed Zbtb20. About half of Zbtb20 + T cells expressed FoxP3, the lineage-defining transcription factor for regulatory T cells (T regs ). Zbtb20 + T regs were phenotypically and genetically distinct from the larger conventional T reg population. Zbtb20 + T regs constitutively expressed mRNA for interleukin-10 and produced high levels of the cytokine upon primary activation. Zbtb20 + T regs were enriched in the intestine and specifically expanded when inflammation was induced by the use of dextran sodium sulfate. Conditional deletion of Zbtb20 in T cells resulted in a loss of intestinal epithelial barrier integrity. Consequently, knockout (KO) mice were acutely sensitive to colitis and often died because of the disease. Adoptive transfer of Zbtb20 + T regs protected the Zbtb20 conditional KO mice from severe colitis and death, whereas non-Zbtb20 T regs did not. Zbtb20 was detected in CD24 hi double-positive and CD62L lo CD4 single-positive thymocytes, suggesting that expression of the transcription factor and the phenotype of these cells were induced during thymic development. However, Zbtb20 expression was not induced in “conventional” T regs by activation in vitro or in vivo. Thus, Zbtb20 expression identified and controlled the function of a distinct subset of T regs that are involved in intestinal homeostasis.

Ribosome biogenesis is a fundamental process required for cell proliferation. Although evolutionally conserved, the mammalian ribosome assembly system is more complex than in yeasts. BCCIP was originally identified as a BRCA2 and p21 interacting protein. A partial loss of BCCIP function was sufficient to trigger genomic instability and tumorigenesis. However, a complete deletion of BCCIP arrested cell growth and was lethal in mice. Here, we report that a fraction of mammalian BCCIP localizes in the nucleolus and regulates 60S ribosome biogenesis. Both abrogation of BCCIP nucleolar localization and impaired BCCIP–eIF6 interaction can compromise eIF6 recruitment to the nucleolus and 60S ribosome biogenesis. BCCIP is vital for a pre-rRNA processing step that produces 12S pre-rRNA, a precursor to the 5.8S rRNA. However, a heterozygous Bccip loss was insufficient to impair 60S biogenesis in mouse embryo fibroblasts, but a profound reduction of BCCIP was required to abrogate its function in 60S biogenesis. These results suggest that BCCIP is a critical factor for mammalian pre-rRNA processing and 60S generation and offer an explanation as to why a subtle dysfunction of BCCIP can be tumorigenic but a complete depletion of BCCIP is lethal.

Viral and parasitic coinfections are known to lead to both enhanced disease progression and altered disease states. HTLV-1 and Strongyloides stercoralis are co-endemic throughout much of their worldwide ranges resulting in a significant incidence of coinfection. Independently, HTLV-1 induces a Th1 response and S. stercoralis infection induces a Th2 response. However, coinfection with the two pathogens has been associated with the development of S. stercoralis hyperinfection and an alteration of the Th1/Th2 balance. In this study, a model of HTLV-1 and S. stercoralis coinfection in CD34+ umbilical cord blood hematopoietic stem cell engrafted humanized mice was established. An increased level of mortality was observed in the HTLV-1 and coinfected animals when compared to the S. stercoralis infected group. The mortality was not correlated with proviral loads or total viral RNA. Analysis of cytokine profiles showed a distinct shift towards Th1 responses in HTLV-1 infected animals, a shift towards Th2 cytokines in S. stercoralis infected animals and elevated TNF-α responses in coinfected animals. HTLV-1 infected and coinfection groups showed a significant, yet non-clonal expansion of the CD4+CD25+ T-cell population. Numbers of worms in the coinfection group did not differ from those of the S. stercoralis infected group and no autoinfective larvae were found. However, infective larvae recovered from the coinfection group showed an enhancement in growth, as was seen in mice with S. stercoralis hyperinfection caused by treatment with steroids. Humanized mice coinfected with S. stercoralis and HTLV-1 demonstrate features associated with human infection with these pathogens and provide a unique opportunity to study the interaction between these two infections in vivo in the context of human immune cells.

The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in December 2019. As similar cases rapidly emerged around the world1–3, the World Health Organization (WHO) declared a public health emergency of international concern on January 30, 2020 and pronounced the rapidly spreading coronavirus outbreak as a pandemic on March 11, 20204. The virus has reached almost all countries of the globe. As of June 3, 2020, the accumulated confirmed cases reached 6,479,405 with more than 383,013 deaths worldwide. The urgent and emergency care of COVID-19 patients calls for effective drugs, in addition to the beneficial effects of remdesivir5, to control the disease and halt the pandemic.

Mesenchymal stem cells (MSCs) have been demonstrated to be anti-inflammatory against various immune disorders through several factors, including indoleamine 2,3-dioxygenase (IDO) and TNF-stimulated gene 6 (TSG-6). However, little is known about the necessity for both of these key immunosuppressive factors. Here we employed the mouse lipopolysaccharide (LPS)-induced acute lung injury (ALI) model, and found that IDO is necessary to achieve the effect of human umbilical cord-derived MSC (hUC-MSC)-based treatment on ALI. Notably, when IDO was deleted or inhibited, the expression of TSG-6 was decreased. This specific IDO-mediated regulation of TSG-6 expression was found to be exerted through its metabolite, kynurenic acid (KYNA), as inhibition of KYNA production led to decreased TSG-6 expression. Importantly, KYNA pretreatment of human MSCs enhanced their therapeutic effect on ALI. Mechanistically, KYNA activates aryl hydrocarbon receptor (AhR), which directly binds to the TSG-6 promoter to enhance TSG-6 expression. Therefore, our study has uncovered a novel link between IDO and TSG-6, and demonstrates that a metabolite of IDO controls the TSG-6-mediated anti-inflammatory therapeutic effects of human MSCs.

Disruption of adenylyl cyclase type 5 (AC5) knockout (KO) is a novel model for longevity. Because malignancy is a major cause of death and reduced lifespan in mice, the goal of this investigation was to examine the role of AC5KO in protecting against cancer. There have been numerous discoveries in genetically engineered mice over the past several decades, but few have been translated to the bedside. One major reason is that it is difficult to alter a gene in patients, but rather a pharmacological approach is more appropriate. The current investigation employs a parallel construction to examine the extent to which inhibiting AC5, either in a genetic knockout (KO) or by a specific pharmacological inhibitor protects against cancer. This study is unique, not only because a combined genetic and pharmacological approach is rare, but also there are no prior studies on the extent to which AC5 affects cancer. We found that AC5KO delayed age-related tumor incidence significantly, as well as protecting against mammary tumor development in AC5KO × MMTV-HER-2 neu mice, and B16F10 melanoma tumor growth, which can explain why AC5KO is a model of longevity. In addition, a Food and Drug Administration approved antiviral agent, adenine 9-β-D-arabinofuranoside (Vidarabine or AraAde), which specifically inhibits AC5, reduces LP07 lung and B16F10 melanoma tumor growth in syngeneic mice. Thus, inhibition of AC5 is a previously unreported mechanism for prevention of cancers associated with aging and that can be targeted by an available pharmacologic inhibitor, with potential consequent extension of lifespan. Fil: De Lorenzo, Mariana S.. State University of New Jersey; Estados Unidos Fil: Chen, Wen. Clemson University; Estados Unidos Fil: Baljinnyam, Erdene. State University of New Jersey; Estados Unidos Fil: Carlini, María José. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncologia "Angel H. Roffo"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: La Perle, Krista. Ohio State University; Estados Unidos Fil: Bishop, Sanford P.. State University of New Jersey; Estados Unidos Fil: Wagner, Thomas E.. Clemson University; Estados Unidos Fil: Rabson, Arnold B.. State University of New Jersey; Estados Unidos Fil: Vatner, Dorothy E.. State University of New Jersey; Estados Unidos Fil: Puricelli, Lydia Ines. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncologia "Angel H. Roffo"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Vatner, Stephen F.. State University of New Jersey; Estados Unidos

Imteyaz Khan,1 Liying Zhang,2 Moiz Mohammed,1 Faith E Archer,1 Jehan Abukharmah,1 Zengrong Yuan,2 S Saif Rizvi,1 Michael G Melek,1 Arnold B Rabson,1,2 Yufang Shi,2 Barry Weinberger,1 Anna M Vetrano1,21Department of Pediatrics, Division of Neonatology, Rutgers Robert Wood Johnson Medical School, 2Rutgers Child Health Institute of New Jersey, New Brunswick, NJ, USABackground: Mesenchymal stem cells (MSCs) have been proposed as autologous therapy for inflammatory diseases in neonates. MSCs from umbilical cord Wharton's jelly (WJ-MSCs) are accessible, with high proliferative capacity. The effects of WJ-MSCs on neutrophil activity in neonates are not known. We compared the effects of WJ-MSCs on apoptosis and the expression of inflammatory, oxidant, and antioxidant mediators in adult and neonatal neutrophils.Methods: WJ-MSCs were isolated, and their purity and function were confirmed by flow cytometry. Neutrophils were isolated from cord and adult blood by density centrifugation. The effects of neutrophil/WJ-MSC co-culture on apoptosis and gene and protein expression were measured.Results: WJ-MSCs suppressed neutrophil apoptosis in a dose-dependent manner. WJ-MSCs decreased gene expression of NADPH oxidase-1 in both adult and neonatal neutrophils, but decreased heme oxygenase-1 and vascular endothelial growth factor and increased catalase and cyclooxygenase-2 in the presence of lipopolysaccharide only in adult cells. Similarly, generation of interleukin-8 was suppressed in adult but not neonatal neutrophils. Thus, WJ-MSCs dampened oxidative, vascular, and inflammatory activity by adult neutrophils, but neonatal neutrophils were less responsive. Conversely, Toll-like receptor-4, and cyclooxygenase-2 were upregulated in WJ-MSCs only in the presence of adult neutrophils, suggesting an inflammatory MSC phenotype that is not induced by neonatal neutrophils.Conclusion: Whereas WJ-MSCs altered gene expression in adult neutrophils in ways suggesting anti-inflammatory and antioxidant effects, these responses were attenuated in neonatal cells. In contrast, inflammatory gene expression in WJ-MSCs was increased in the presence of adult but not neonatal neutrophils. These effects should be considered in clinical trial design before WJ-MSC-based therapy is used in infants.Keywords: inflammation, umbilical cord, apoptosis, neutrophil, mesenchymal stem cells

Although the mechanisms by which the HTLV-I Tax oncoprotein activates the two NF-κB signaling pathways have been well studied, there is still no convincing evidence demonstrating a functional role for NF-κB in the Tax-mediated tumorigenesis or HTLV-I-mediated adult T-cell leukemia/lymphoma (ATL). Moreover, how Tax is negatively regulated by cellular factors has not yet been explored. Using various transgenic mice and cells deficient in different key IKK/NF-κB signaling components, we have defined the differential but cooperative roles of the canonical and noncanonical NF-κB pathways in Tax-mediated tumorigenesis. One function of non-canonical NF-κB activation is to repress expression of the wwox tumor suppressor gene, which in turn facilitates Tax-induced canonical NF-κB activation. Mechanistic studies indicate that WWOX blocks Tax-induced IKKalpha recruitment and subsequent RelA phosphorylation. Furthermore, we have identified PDLIM2, an essential terminator of canonical NF-κB activation, as a negative regulator of Tax. PDLIM2 directly binds to and shuttles Tax from its activation sites to the nuclear matrix for ubiquitination-mediated degradation, thereby suppressing the tumorigenicities of HTLV-I- or Tax-transduced cells. Interestingly, PDLIM2 expression is epigenetically downregulated in HTLV-I-transformed T cells and primary ATL cells. These studies suggest that the counterbalance between PDLIM2 and HTLV-I may determine the ATL leukemogenesis and provide the first line of genetic evidence demonstrating the functional significance of NF-κB in Tax-mediated tumorigenesis. These studies also define, for the first time, a delicate cooperation of the two pro-oncogenic NF-κB pathways in tumorigenesis and a functional role of the WWOX tumor suppressor in NF-κB regulation and viral tumorigenesis.

The pathogenesis of HTLV-1-associated diseases involves complex interactions between HTLV-1 and the infected host, and is dependent on viral replication and gene expression. Previous studies from our laboratory have shown that T cell receptor- and phorbol ester (PMA)-mediated stimulation of chronically infected CD4 T-cells increases the expression of integrated HTLV-1 proviruses. Detailed analysis of HTLV-1 RNA and protein species following PMA treatment of the FS and SP HTLV-1-infected T cells demonstrated rapid induction of tax/rex mRNA peaking prior to other HTLV-1 RNA species. This rapid increase in tax/rex mRNA was associated with markedly enhanced tax/rex mRNA stability. (from 3.5 hr to >24hr in treated cells), while the stability of unspliced or singly spliced HTLV1 RNAs did not increase. PMA treatment also increased RNA transcription. These data contrast with a delayed increase in HTLV-1 RNA transcription following treatment the HDAC inhibitor, SAHA. To further identify the elements and mechanisms responsible for enhanced tax/rex RNA stability, we adapted a luciferase reporter assay in which tax/rex cDNA sequences were linked to the 3’ end of luciferase gene. Increased luciferase activity was observed with this reporter plasmid upon PMA treatment, as compared with a reporter plasmid containing tax antisense sequences. Our data support a model whereby T cell activation leads to increased HTLV-1 gene expression through increased tax/rex mRNA stability, which in turn results in induction of Tax protein expression, and further activation of HTLV-1 gene expression, and associated changes in cellular gene expression, contributing to increased T cell survival and proliferation and disease.

In a recent Cell Death and Disease article, Liu et al.1 reported a striking observation that portal vein infusion of autologous bone marrow (ABM) in four AIDS patients with severe liver cirrhosis resulted not only in significant clinical improvement of liver function but also a sustained enhancement of CD4+ T-cell levels, as shown schematically in Figure 1. These results raise the important possibility that ABM infusion, in context of concurrent liver disease, can result in CD4+ T-cell reconstitution in AIDS patients. This provocative study, although performed on only a few patients, raises a number of fascinating questions, both mechanistic and therapeutic. Figure 1 Schematic representation of the results of Liu et al.1 showing that intrahepatic infusion of ABM resulted in enhanced liver function and sustained CD4+ cell increases in patients with liver cirrhosis and AIDS In the absence of liver transplantation, the traditional treatment of late-stage, cirrhotic liver disease has generally involved symptomatic therapies to avert life-threatening complications, such as severe portal hypertension and hepatic encephalopathy. More recently, reversibility of hepatic fibrosis has been demonstrated following antiviral therapy in virally induced cirrhosis.2 Other studies have focused on directing regeneration of functional hepatocytes, and cellular therapies of chronic liver disease have begun to be tested.3 In human clinical trials, ABM infusion in late-stage cirrhotic patients resulted in marked improvements in hepatic function,4 similar to those seen in the patients studied by Liu et al.1 here, and splenectomy similarly markedly enhanced the effects of ABM infusion.5 ABM infusion was effective in both virally and non-virally caused cirrhosis, suggesting that antiviral activity is not the responsible mechanism. The mechanisms responsible remain largely unknown; however, animal studies suggest that infused bone marrow (BM) cells make matrix metalloproteinases that can remodel and remove fibrous tissue.6 One major difference between this study and the previous studies was the direct infusion of ABM into the portal vein; However, both intrahepatic artery and portal vein infusions of BM cells have been used by other groups.6 A critical question is which cells in the infused BM contribute to the response. Although it was initially hypothesized that hematopoietic stem cells (HSCs) had a critical role, more recent work suggests that mesenchymal stem cells (MSCs)6, 7 may be the key cellular element, potentially through their anti-inflammatory and wound healing properties. MSC production of cytokines has been postulated to be the major effector of MSC immune and tissue modulatory functions,8 and recent studies implicating increased G-CSF and IL-1β in the healing liver, post ABM infusion9 are consistent with this hypothesis. Specific studies of the effects of BM-derived MSCs on liver fibrosis will help to answer this question. The most striking aspect of the Liu et al.1 paper was the persistent increase in CD4+ T cells following ABM infusion in these AIDS patients with cirrhosis. Stable reconstitution of CD4+ T-cell number and function, with complete suppression of viral replication and elimination of viral reservoirs, has been the ‘holy grail' of AIDS therapy.10 Such CD4+ T-cell restoration would require HSCs capable of generating new CD4+ T cells that can resist future HIV infection. These could come from endogenous HSCs or from cellular therapies, such as HSC transplantation.11 In fact, the only documented ‘cure' of HIV infection remains in the German AIDS patient who underwent BM transplantation (BMT) from a CCR5 Δ32 homozygous donor (with decreased binding to R5-tropic HIV strains) as treatment for acute leukemia.12 HIV viral loads in this patient have remained undetectable even in the absence of antiretroviral therapy. These results have prompted more systematic efforts to develop CCR5-mutated HSCs as a more broadly available HIV therapy, either as banked, naturally mutated umbilical cord blood HSCs13 or as genetically modified autologous HSCs.14 Recent studies suggest that BMT from CCR5-wild-type, allogeneic donors may have a beneficial, perhaps even ‘curative' effect as well, potentially through a graft-versus-HIV effect, supplying an efficient anti-HIV T-cell response.15 Autologous BMT (ABMT) represents an alternative approach, which would not have the graft-versus-HIV effect but would be less toxic. ABMT is becoming more common in AIDS patients with malignancies;16 however, in these settings, is accompanied by chemotherapy that has marked inhibitory effects on the host-immune response. A careful investigation of the mechanism of CD4+ T-cell increase is now required. Questions abound at multiple levels: Are the increased numbers of CD4+ T cells functional, and have these patients regained ‘meaningful' T-cell help?11 Ex vivo assays of T-cell function could provide some indication of this. An even more basic question is whether de novo production of CD4+ T cells following ABM infusion is responsible for the observed increase? This question is answerable by analysis of TRECs (T-cell receptor excision circles found in recently produced T cells), which can confirm production and release of new T cells into the periphery.17 Alternatively, does ABM infusion lead to increased half-life of existing CD4+ T cells? This is unlikely based on studies of T-cell kinetics with highly active antiretroviral therapies (HAART) alone.11 Past studies have tested the effects of infusion of autologous CD8+ T cells in HIV patients with some therapeutic effect;18 however, this is unlikely to explain the increase in CD4+ T cells. Does the coupling of HAART with ABM infusion lead to a more significant effect, allowing the infused hematopoietic cells to persist and to generate new CD4+ T cells? Does the route of infusion (portal vein) have an unexpected role in supporting CD4+ T-cell production and viability? As with the restoration of liver function in these patients, it will be critical to define the cells in the ABM that are responsible for increased CD4+ T cells. Is this a direct reconstitution of the CD4+ T-cell compartment by progeny of infused HSCs? There was no attempt to purge the BM cells of HIV+ cells. Would purging of HIV-infected cells through ex vivo manipulation potentially enhance efficacy or is it irrelevant? Do MSCs have a role by virtue of their profound immunomodulatory activity? Although some types of MSCs have been shown to be infectable by HIV,19 there has been little study of the effect of either resting or cytokine-activated MSCs on HIV infection. It is interesting that increases in CD4+, CD25+ T cells have also been observed following ABM infusions undertaken for the treatment of autoimmune disorders, suggesting induction of an as yet unknown regulatory network enhancing CD4+ T-cell production.20 Clearly, it is essential that these studies of CD4+ T-cell reconstitution be replicated in larger, controlled patient cohorts, including patients with and without liver disease, to more clearly define the general applicability of ABM infusion in the presence of highly effective antiretroviral therapies. Careful analysis of T-cell function, anti-HIV immune responses and viral load are also essential in future studies. The relatively low, initial CD4+ levels in these patients, even though proviral loads were controlled by HAART, raises the important question of whether similar increases would be observed in patients who have had more significant stable increases in CD4+ T cells from antiretroviral treatment alone. Issues regarding route of administration of BM cells also need to be addressed. This study by Liu et al.1 clearly offers a novel window into the critical goal of true reconstitution of immune response in patients with AIDS, and as such is provocative and noteworthy.

Infection with the human T-cell leukemia virus-1 (HTLV-1) is associated with a range of outcomes ranging from asymptomatic infection, to the development of HAM/TSP and adult T cell leukemia/lymphoma. Pathogenesis of these disorders involves complex interactions with the host immune system. Our previous studies showed that phorbol ester (PMA) and T cell receptor (TCR)-mediated activation of chronically infected CD4 T cells increased expression of HTLV-1 gene products [1]. We hypothesized that immune activation of infected T cells may play an important role in disease pathogenesis through induction of Tax expression resulting in increased survival and proliferation. To test this, we employed transgenic mice in which Tax is regulated by the HTLV-1 LTR. These mice develop neurofibromas, but do not express Tax in T cells and do not develop lymphomas [2]. TCR stimulation of transgenic LTR-Tax CD4+ T cells induced Tax expression, early hyper-proliferation, and long-term growth in culture. Survival of these cells was accompanied by transiently increased expression of mcl-1. Long-term surviving cells exhibited a CD4+CD25+CD3- phenotype commonly observed in ATL. Engraftment of immune-activated LTR-Tax CD4+ T-cells into NOD/Shi-scid/IL-2Rγ null mice resulted in a leukemia-like phenotype. Immune activated Tax CD4+ T cells express characteristics of several different CD4+ T cell subtypes, suggesting that HTLV-1 Tax induces changes in the normal pattern of CD4+ subtype specification. We also investigated mechanisms of HTLV-1 activation following PMA stimulation. Surprisingly, PMA treatment was associated with a rapid, marked stabilization of HTLV-1 tax/rex mRNA. Increased RNA stability represents a novel mechanism for increasing HTLV-1 gene expression in chronically infected cells.

The mechanism of the antiviral activity of hypericin was characterized and compared with that of rose bengal. Both compounds inactivate enveloped (but not unenveloped) viruses upon illumination by visible light. Human immunodeficiency and vesicular stomatitis viruses were photodynamically inactivated by both dyes at nanomolar concentrations. Photodynamic inactivation of fusion (hemolysis) by vesicular stomatitis, influenza, and Sendai viruses was induced by both dyes under similar conditions (e.g., I50 = 20-50 nM for vesicular stomatitis virus), suggesting that loss of infectivity resulted from inactivation of fusion. Syncytium formation, between cells activated to express human immunodeficiency virus gp120 on their surfaces and CD4+ cells, was inhibited by illumination in the presence of 1 microM hypericin. Hypericin and rose bengal thus exert similar virucidal effects. Both presumably act by the same mechanism--namely, the inactivation of the viral fusion function by singlet oxygen produced upon illumination. The implications of this photodynamic antiviral action for the potential therapeutic usefulness of both hypericin and rose bengal are discussed.

Address: 1Child Health Institute of New Jersey, University of Medicine and Dentistry of New Jersey (UMDNJ), Robert Wood Johnson Medical, School (RWJMS), 89 French Street, New Brunswick, New Jersey 08901, USA, 2Department of Molecular Genetics, Microbiology, and Immunology UMDNJ-RWJMS, 661 Hoes Lane, Piscataway, New Jersey 08854, USA and 3Cancer Institute of New Jersey UMDNJ-RWJMS, 179 Little Albany Street, New Brunswick, NJ 08903, USA * Corresponding author

The adeno-associated virus (AAV) rep gene encodes four proteins (Rep78, Rep68, Rep52, and Rep40) required for AAV DNA replication and AAV gene regulation. In addition, the Rep proteins may have pleiotropic regulatory effects in heterologous systems, and in particular Rep78 may mediate a negative regulatory effect. We analyzed the effects of the AAV rep gene on human immunodeficiency virus type 1 (HIV-1) gene expression. The rep gene proteins of AAV type 2 (AAV2) inhibited the trans-activating ability of HIV-1. Constructs containing the AAV2 rep gene (pHIVrep) or a CAT gene (pBennCAT) expressed from the 5' HIV-1 long terminal repeat were inducible for Rep78 and Rep68 or CAT expression, respectively, when cotransfected with a plasmid containing the HIV-1 tat gene (pARtat). When equivalent amounts of pHIVrep and pBennCAT were cotransfected with increasing amounts of pARtat, expression of CAT activity was decreased. The pHIVrep construct was more inhibitory than plasmids expressing rep from the wild-type AAV2 p5 transcription promoter. rep expression from pHIVrep almost completely inhibited the replication of an HIV-1 proviral clone as measured by reverse transcriptase activity and p24 protein levels. Inhibition of HIV-1 production by Rep protein was also seen at the transcriptional level in that all HIV-1 transcripts were decreased when pHIVrep was present. The inhibitory effects of pHIVrep appear to be mediated primarily by Rep78 and perhaps Rep68. These results suggest that a trans-acting protein from a heterologous virus might be used to inhibit HIV-1 growth.

Replication of HIV-1 requires Tat, which stimulates gene expression through a target sequence, TAR. It is known that TAR is a Tat-responsive target. Since Tat increases transcriptional initiations from the HIV-1 LTR promoter, it is unclear mechanistically how Tat utilizes an RNA target. Here we show that TAR RNA is only one component of the Tat-responsive target. Efficient Tat trans -activation was observed only when TAR was present in conjunction with the HIV-1 LTR NF-κB/SP1 DNA sequences. TAR RNA outside of this context produced a suboptimal Tat response. We propose that TAR RNA serves an attachment function directing Tat to the LTR. A Tat protein engineered to interact with LTR DNA could trans -activate through a TAR-independent mechanism. This suggests that Tat also has a DNA target.

Summary Mesenchymal stromal cells (MSCs) tend to infiltrate into tumors and form a major component of the tumor microenvironment. These tumor-resident MSCs are known to affect tumor growth, but the mechanisms are largely unknown. We found that MSCs isolated from spontaneous lymphomas in mouse (L-MSCs) strikingly enhanced tumor growth in comparison to bone marrow MSCs (BM-MSCs). L-MSCs contributed to greater recruitment of CD11b + Ly6C + monocytes, F4/80 + macrophages, and CD11b + Ly6G + neutrophils to the tumor. Depletion of monocytes/macrophages, but not neutrophils, completely abolished tumor promotion of L-MSCs. Furthermore, L-MSCs expressed high levels of CCR2 ligands, and monocyte/macrophage accumulation and L-MSC-mediated tumor promotion were largely abolished in CCR2 −/− mice. Intriguingly, TNFα-pretreated BM-MSCs mimicked L-MSCs in their chemokine production profile and ability to promote tumorigenesis of lymphoma, melanoma, and breast carcinoma. Therefore, our findings demonstrate that, in an inflammatory environment, tumor-resident MSCs promote tumor growth by recruiting monocytes/macrophages.

We characterized the structure of human endogenous retroviral env RNA transcripts by Northern blot hybridization and cDNA cloning. Polyadenylated 3.0- and 1.7-kilobase env RNAs can be identified in placenta, colon carcinoma, and breast carcinoma cells. We have obtained partial cDNA clones of both size classes of RNAs. Both env RNAs contained putative gp70 coding sequences; the 1.7-kilobase species, however, lacked sequences in the 3' env region which could specify a p15E analog. Both cDNA clones contained in-frame termination codons; thus, neither could encode full-length env proteins.

Mutations were introduced into the regulatory sequences in the long terminal repeat of an infectious molecular clone of the human immunodeficiency virus. Viruses in which the NF-kappa B binding sites were deleted or ones in which one or two Sp1 binding sites were mutated still replicated efficiently in human T lymphocytes. A deletion of the two NF-kappa B sites plus the three Sp1 sites or a mutation of the tat-responsive region rendered the virus replication incompetent. Thus, the NF-kappa B sequences are not required for human immunodeficiency virus infectivity; however, a tat-responsive region is essential.

Human immunodeficiency virus type 1 (HIV-1) trans-activator protein Tat activates the expression of its viral long terminal repeat (LTR) through a target transactivation-responsive element termed TAR. We have constructed cell lines that constitutively express the HIV-1 Tat protein. Analyses of nuclear proteins from these cells and from matched control cells that do not express Tat have identified three proteins that bind to a radiolabeled HIV-1 TAR RNA probe. These polypeptides are 100 kDa, 62 kDa, and 46 kDa in size. Competition experiments using a wild-type TAR RNA sequence, a biologically inactive mutant sequence of TAR, and an unrelated RNA species demonstrated that these proteins show higher binding affinity to wild-type TAR than to the other two non-trans-activatable sequences. We hypothesize that these cellular proteins may mediate a function necessary in Tat-dependent activation of the LTR. The fact that no differences were seen in the binding profiles of nuclear proteins to TAR RNA in Tat-producing and Tat-nonproducing cells suggests that Tat does not directly interact with TAR.