Dispensable role of the NF-kappa B sites in the UV-induction of the HIV-1 LTR in transgenic mice

Insulin-like growth factor-1 downregulates nuclear factor kappa B activation and upregulates interleukin-8 gene expression induced by tumor necrosis factor alpha

Pretreatment of HT29-D4 epithelial adenocarcinoma colic cells with des-IGF-1 upregulated TNF alpha-mediated activation of IL-8 expression at different levels (protein, mRNA, and hnRNA). RNA transcription but not RNA stabilization was found to be involved. In this cell line, cooperation of NF-kappa B with other factors appeared essential for IL-8 expression. Indeed, TNF alpha-induced NF-kappa B translocation was not sufficient to support enhancement of the transcription and des-IGF-1 did not promote but partly inhibited both the TNF alpha-induced NF-kappa B activation and I kappa B alpha degradation through a PI-3K-dependent pathway. A CCAAT/enhancer binding protein (C/EBP) site located on the IL-8 gene enhancer cooperated with a NF-kappa B binding site and led to the upregulation of IL-8 expression. Binding of C/EBP alpha to this sequence disappeared in IGF-1 treated cells. This event may be important for the cross-talk between IGF-1- and TNF alpha-mediated pathways leading to the control of inflammatory processes and the decision concerning apoptosis or cell survival.

UV-enhanced expression of a reporter gene is induced at lower UV fluences in transcription-coupled repair deficient compared to normal human fibroblasts, and is absent in SV40-transformed counterparts

UV irradiation enhances transcription of a number of cellular and viral genes. We have compared dose responses for alterations in expression from reporter constructs driven by the human and murine cytomegalovirus (CMV) immediate early (IE) promoters in cells from patients with deficiencies in nucleotide excision repair (complementation groups of xeroderma pigmentosum and Cockayne syndrome) following UV exposure, or infection with UV-damaged recombinant vectors. Results suggest that unrepaired damage in active genes triggers increased reporter activity from constructs driven by the CMV promoters in human fibroblasts. Similar to human fibroblasts, HeLa cells and cells from Li-Fraumeni syndrome patients (characterized by an inherited mutation in the p53 gene) also displayed an increase in reporter activity following UV exposure; however, this response was absent in all simian virus 40 (SV40)-transformed cell lines examined. This suggests that a pathway affected by SV40-transformation (other than p53) plays an essential role in UV-enhanced expression from the CMV IE promoter.

Role of the p38 and MEK-1/2/p42/44 MAP kinase pathways in the differential activation of human immunodeficiency virus gene expression by ultraviolet and ionizing radiation

Ultraviolet (UV) radiation is a potent activator of human immunodeficiency virus (HIV) gene expression in a HeLa cell clone having stably integrated copies of an HIV cat (cat gene under control of the HIV promoter) reporter construct, whereas ionizing radiation is ineffective. UV-activated HIV gene expression is completely blocked by the specific p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 and by expression of a kinase-inactive p38 mutant that interferes with normal p38 function, suggesting that this stress-activated protein kinase plays an important role in UV-mediated transcriptional activation of HIV. In support of these findings, we show here that Western blot analysis demonstrated rapid and significant activation of p38 MAP kinase by UV. On the other hand, gamma-radiation activated p38 MAP kinase very poorly in HeLa cells at both low and high doses at times (5-30 min) when UV radiation was effective. UV radiation also activated HIV gene expression (< or = 9-fold) in 1G5 Jurkat T-cells stably transfected with a luciferase reporter gene under control of the HIV promoter. In these cells, gamma-radiation stimulated HIV gene expression but to a lesser extent (< or = 3-fold) and with different kinetics than after UV radiation, and this response was obliterated by the incubation of cells with the mitogen-activated protein kinase/Erk kinase (MEK)-1/2 inhibitor PD98059. This result suggests that in these cells signaling in response to gamma-radiation is transduced through the MEK-1/2/p42/44 MAP kinase pathway to increase HIV gene expression. All combined, these results suggest that activation of p38 MAP kinase is necessary for efficient HIV gene expression triggered by DNA damaging agents, and, in a cell type-specific manner, activation of the MEK-1/2/p42/44 MAP kinase pathway is important for triggering a response to gamma-radiation. Thus, it appears as if UV signaling leading to HIV gene expression requires the p38 MAP kinase pathway whereas activation by gamma-radiation requires the MEK-1/2/p42/44 MAP kinase pathway.

Activation of NF-kappa B and p38 MAP kinase is not sufficient for triggering efficient HIV gene expression in response to stress

Recent studies have established an essential role for p38 MAP kinase in UV activation of human immunodeficiency virus (HIV) gene expression. However, p38 MAP kinase is not involved in activation of NF-kappa B, a key transcriptional activator of HIV gene expression, in response to UV, suggesting that NF-kappa B acts independently of p38 MAP kinase. In this study, we have investigated whether activation of HIV gene expression occurs when p38 MAP kinase and NF-kappa B are activated by separate stress-causing treatments, each relatively specific for activating only one of the factors. Treatment of cells with sorbitol (hyperosmotic shock) strongly activates p38 MAP kinase, whereas the cytokine TNF-alpha is a poor activator of p38 MAP kinase. On the other hand, TNF-alpha is a strong activator of NF-kappa B whereas sorbitol is not. Sorbitol, however, activates AP-1 DNA binding activity in a manner similar to that of UV. Most importantly, both sorbitol and TNF-alpha are poor activators of HIV gene expression in HeLa cells stably transfected with an HIVcat reporter gene, whereas UV elicits a strong response. The combined treatment with UV and hyperosmotic shock produces an additive effect on HIV gene expression, suggesting that these agents activate at least in part by different mechanisms. The combined treatment with sorbitol and TNF-alpha activates p38 and NF-kappa B to levels similar to those with UV, yet only results in 25-30% of the CAT levels elicited by UV. Inhibition of NF-kappa B activation by the protease inhibitor N-alpha-tosyl-L-phenylalanine chloromethyl ketone (TPCK) prevents UV activation of HIV gene expression, but does not inhibit p38 MAP kinase activation. We conclude that whereas both p38 MAP kinase and NF-kappa B are important for UV activation of HIV gene expression they act independently from each other and activation of both factors is not sufficient for triggering a full HIV gene expression response. Activation of HIV gene expression by UV must therefore involve additional cellular processes, such as those triggered by DNA damage, for generation of a full gene expression response.

Genetic evidence that stress-activated p38 MAP kinase is necessary but not sufficient for UV activation of HIV gene expression

We have examined the role of stress-activated p38 MAP kinase in regulating human immunodeficiency virus (HIV) gene expression in response to ultraviolet light (UV). We found that UV activated p38 in HeLa cells harboring stably integrated copies of an HIVcat plasmid to levels similar to those obtained by hyperosmotic shock. However, hyperosmotic shock resulted in one order of magnitude smaller increase in CAT activity than treatment with UV. The specific p38 inhibitor SB203580 significantly decreased (>80%) UV activation of HIV gene expression whereas PD98059, a specific MEK-1 inhibitor did not, suggesting that p38 is specifically involved in the HIV UV response and little to no contribution is provided by MEK-1 and the p42/p44 MAP kinase pathway. Whereas increased binding of NF-kappaB to an oligonucleotide spanning the HIV enhancer was observed after UV, as expected, this binding was not affected by SB203580. Furthermore, UV activation of HIV gene expression in cells having the cat reporter gene under control of an HIV promoter deleted of the enhancer (-69/+80) produced results indistinguishable from those using HIVcat/HeLa cells with an intact HIV promoter (-485/+80), suggesting that SB203580 acts through the basal transcription machinery. Northern blot analysis of steady-state RNA from HIVcat/HeLa cells revealed an almost complete inhibition of UV activation with SB203580 at the RNA level. Similarly, the UV response was almost completely obliterated at the CAT and RNA levels in HIVcat/HeLa cells stably transfected with a plasmid expressing a kinase-inactive mutant of p38 (isoform alpha), without affecting NF-kappaB activation, providing strong genetic evidence that p38, at least the alpha isoform, is necessary for UV activation of HIV gene expression and that NF-kappaB activation alone is insufficient. These results firmly establish p38 MAP kinase as a key modulator of HIV gene expression in response to UV that acts independently of NF-kappaB.

Secretion of extracellular factor(s) induced by X-irradiation activates the HIV type 1 long terminal repeat through its kappaB motif

X-irradiation has been used in the treatment of several human diseases, including AIDS-related-malignancies. X-irradiation might induce the transcription and the replication of human immunodeficiency virus type 1 (HIV-1) and enhance nuclear factor kappa B (NF-kappaB). In the present article we show that the activation of the HIV-1 long terminal repeat (LTR) by direct X-irradiation can be mimicked by coculture of transfected cells with X-irradiated nontransfected (HIV-1-negative) cells. In the human colonic carcinoma cell line HT29, the activation seems to depend on an extracellular factor(s) released by a cell line treated with X-rays. The HIV-1 LTR cis-acting element conferring X-indirect responsiveness was identified as the kappaB tandem motif. The two main nuclear HIV-1 kappaB-binding complexes activated by X-direct and -indirect irradiation were the NF-kappaB p50/p65 and c-Rel/p65 heterodimers. Nuclear NF-kappaB activation was dependent on protein neosynthesis. It was partially inhibited by 100 microM pyrrolidine dithiocarbamate, a potent antioxidant drug, but was not correlated with a significant decrease in cellular IkappaBalpha. Furthermore, X-irradiation induces the expression of several cytokine genes generally associated with stress response and antibodies against interleukin 6 and TNF-alpha partially inhibited the X-indirect activation of the HIV-1 LTR. The use of protein kinase C (PKC)-specific inhibitor and of forskolin, an adenylate cyclase activator, suggests that a PKC-dependent pathway and the cAMP intracellular concentration could play a role in the X-indirect enhancement of HIV-1 LTR transcription in the HT29 cell line. In addition, supernatants of an X-irradiated HT29 cell culture activated the HIV-1 stimulation in infected peripheral blood monocytes.

Cell-to-cell contact activates the long terminal repeat of human immunodeficiency virus 1 through its kappaB motif

Cell-to-cell contact between peripheral blood lymphocytes and transfected human colonic carcinoma cell line HT29 activates transcription of the long terminal repeats (LTR) of human immunodeficiency virus. HIV-1 LTR transcription is controlled by a complex array of virus-encoded and cellular proteins. Using various constructs expressing a lacZ reporter gene under the control of the intact or three deleted forms of HIV-1 LTR, we obtained evidence that the kappaB regulatory elements located in the U3 region are involved in cell-to-cell activation of HIV-1 LTR. Cell-to-cell contact activates in vitro binding of the nuclear factor kappaB (NF-kappaB) p50/p65 heterodimer to an HIV-1 kappaB oligonucleotide. Cell-to-cell contact activation of NF-kappaB was only partially inhibited by 100 microM pyrrolidine dithiocarbamate and was not correlated with a significant decrease of cellular inhibitor kappaB alpha. NF-kappaB nuclear activation was not detectable before 1 h after cell contact and was dependent on protein synthesis.

Activation of the HIV type 1 long terminal repeat by X-irradiation involves two main Re1/NF-kappa B DNA-binding complexes

Transcription of human immunodeficiency virus type 1 (HIV-1) is regulated by multiple cis-acting regulatory elements located in the viral long terminal repeats (LTRs). HIV-1 LTR enhancer is activated by a variety of heterologous viral, chemical, and physical agents. Studies have demonstrated that irradiation by X-rays induces transcription under the control of the HIV-1 LTR and that ionizing radiations activate DNA binding of the nuclear transcription factor NF-kappa B. Using various constructs expressing a reporter gene under the control of complete or deleted LTRs of HIV-1, we evidenced that a sequence located in the U3 region was involved in X-ray activation of the HIV-1 LTR in the human colonic carcinoma cell line HT29. The cis-acting element conferring X-ray responsiveness is indistinguishable from HIV NF-kappa B tandem repeat binding sites (HIV-1, kappa B). The present work has examined the effects of X-irradiation on the NF-kappa B transcription factor. Furthermore, we characterized the subunit composition of the two major nuclear NF-kappa B complexes that bind HIV-1 kappa B after X-ray irradiation.

UVB irradiation upregulation of the Drosophila 1731 retrotransposon LTR requires the same short sequence of U3 region in a human epithelial cell line as in Drosophila cells

Phylogenetic analysis of the retrotransposon and retrovirus suggests an evolutionary relationship between them and indicates that transactivation of the long terminal repeat (LTR)-containing retroelements could be ubiquitous. Using constructs expressing a reporter gene under the control of the entire or deleted LTR of 1731, which is a retrotransposable element of Drosophila melanogaster, we were able to show that the UVB-irradiation activation of the 1731-LTR requires the same short sequence of U3 region in a human epithelial cell line as in Schneider's Drosophila cell line (S2). This sequence is similar to the binding sequence of the members of the nuclear factor-kappa B (NF-kappa B)/rel family. In addition, human colonic carcinoma cells (HT29), in response to UVB-irradiation, produce some extracellular factor(s) that activates the 1731-LTR in nonirradiated cells.

Signal transduction and HIV transcriptional activation after exposure to ultraviolet light and other DNA-damaging agents

Short wavelength (254 nm) ultraviolet light (UVC) radiation was much more potent in activating transcription of human immunodeficiency virus 1 (HIV) reporter genes stably integrated into the genomes of human and monkey cells than ionizing radiation (IR) from a 137Cs source at similarly cytotoxic doses. A similar differential was also observed when c-jun transcription levels were examined. However, these transcription levels do not correlate with activation of nuclear factor (NF)-kappa B and AP-1 measured by band-shift assays, i.e. both types of radiation produce similar increases in NF-kappa B and AP-1 activity, suggesting existence of additional levels of regulation during these responses. Because of the well-established involvement of cytoplasmic signaling pathways in the cellular response to tumor necrosis factor-alpha (TNF-alpha), UVC, and IR using other types of assays, the role of TNF-alpha in the UVC response of HIV and c-jun was investigated in our cell system. We demonstrate that UVC and TNF-alpha activate HIV gene expression in a synergistic fashion, suggesting that it is unlikely that TNF-alpha is involved in UVC activation of HIV transcription in stably transfected HeLa cells. Moreover, maximum TNF-alpha stimulation resulted in one order of magnitude lower levels of HIV expression than that observed after UVC exposure. We also observed an additive effect of UVC and TNF-alpha on c-jun steady-state mRNA levels, suggestive of a partial overlap in activation mechanism of c-jun by UVC and TNF-alpha; yet these responses are distinct to some extent. Our results indicate that the HIV, and to some extent also the c-jun, transcriptional responses to UVC are not the result of TNF-alpha stimulation and subsequent downstream cytoplasmic signaling events in HeLa cells. Additional levels of regulation that do not directly involve the NF-kappa B and AP-1 transcription factors, such as changes in chromatin structure associated with the UV repair process, may also be important for a full transcriptional response of HIV and c-jun to UVC. In addition to the new data, this report also summarizes our current views regarding UVC-induced activations of HIV gene expression in stably transfected cells.

Transgenesis in rats: technical aspects and models

The production of transgenic rats by DNA-microinjection into fertilized ova has now become an established procedure, although fewer than 20 lines have been described during the last 5 years. Overall, transgenic rats remain more difficult to produce than transgenic mice, but satisfactory yields have been obtained by several laboratories. A review of the methods used to generate transgenic rats shows considerable variation between different laboratories, particularly in choice of strain, superovulation protocols and the use of embryo culture before reimplantation. In some instances, the production of transgenic rats has provided data that are new and relevant, compared to data obtained in mice bearing the same transgene. Models have been developed for human diseases such as hypertension and autoimmunity, and applications have been found in the study of carcinogenesis and in pharmacological research. Transgenic rat technology also opens up interesting perspectives for transplantation research, in which microsurgery is an essential procedure. Intensive research is in progress in several laboratories to produce rat embryonic stem (ES) cell lines, but existing lines have not participated in germ line formation a prerequisite for their use in gene knock out experiments.

Transgenic and knockout mice in the study of neurodegenerative diseases

Accurate animal models are essential for detailed analysis of the mechanisms underlying human neurodegenerative diseases. In addition, they can offer useful paradigms for the development and evaluation of new therapeutic strategies. We review the most popular techniques for modification of the mammalian genome in vivo, and provide a critical evaluation of the available transgenic mouse models for several neurological conditions of humans, including prion diseases, human retroviral diseases, Alzheimer's disease, and motor neuron diseases.

Transgenic models of human immunodeficiency virus type-1

Transgenic models have provided significant insights into HIV-1 pathogenesis, particularly with regards to Kaposi's sarcoma. HIV-associated nephropathy, the tissue-restricted expression of CNS strains of HIV-1, and the function of Nef in vivo. Both multigenic and single gene constructs have contributed to our understanding of HIV-1-induced diseases. While failing to provide models suitable for vaccine development, these transgenic models have provided great insight into HIV pathogenesis and may yet provide a means for the development and testing of molecular based therapies for AIDS.

Physical contact with lymphocytes is required for reactivation of dormant HIV-1 in colonic epithelial cells: involvement of the HIV-1 LTR

HIV-1 transmission from mucosal epithelial cells to lymphocytes is a potential mechanism of HIV-1 contamination during sexual intercourse. The human colon epithelial cell line HT-29, that is infectable by various HIV-1 strains, is a useful model for studying the molecular mechanisms involved in this process. In the present study, we show that HT-29 cells, when exposed to either HIV-1(LAI) or HIV-1(NDK) at a low multiplicity of infection, became infected but did not produce infectious virions. Using two-compartment cell culture chambers separated by a porous membrane, we showed that PBL were able to rescue infectious HIV-1 from latently infected HT-29 cells following a physical interaction between the two cell populations. In contrast, HT-29 cells, infected with the same viruses at a high multiplicity of infection, were able to produce mature viral particles that were infectious to PBL in absence of cellular contacts. Transient expression assays using an indicator gene under the control of the HIV-1 long terminal repeat revealed that cell-to-cell contact induced an activation of the HIV-1 promoter. These observations provide a putative molecular mechanism for transmission of HIV-1 from mucosal epithelial cells to lymphocytes.

Hepatitis B virus X gene product acts as a transactivator in vivo

It has previously been shown that the hepatitis B virus X gene product, pX, transactivates homologous and heterologous transcriptional regulatory sequences of viruses and various cellular genes in vitro. However, there is no evidence about the reproducibility and the relevance of this phenomenon in vivo. In this study we crossbred transgenic mice expressing the X gene under the control of the human antithrombin III (ATIII) gene regulatory sequences with transgenics carrying either the chloramphenicol acetyl-transferase or the LacZ bacterial reporter genes driven by the HIV1-LTR, which is known to be activated in trans by pX. Expression of pX in the liver stimulates the HIV1-LTR driven expression of both chloramphenicol acetyl-transferase and beta-galactosidase reporter genes in double transgenic mice. No detectable increase in chloramphenicol acetyl-transferase expression was observed in tissues, such as the spleen, brain and heart, that do not express pX. Our results confirm the transactivating properties of pX in vivo for the first time and support the hypothesis that pX might indeed modify gene expression in HBV-infected hepatocytes and influence viral pathogenesis.

Activation of HIV type 1 long terminal repeat by ultraviolet light is serum and strain specific

We have studied the UV responsiveness of xeroderma pigmentosum (XP) and HeLa cell lines transfected with a CAT reporter gene under the control of the HIV-1 LTR promoter. XP fibroblasts grown in 10% newborn bovine serum (NBS) were three times more responsive to UV radiation than cells grown in 10% fetal calf serum (FCS). Moreover, cocultivation of UV-irradiated XP cells with XP cells containing stable integrants of HIV-LTR CAT was found to be more than four times more effective in inducing the CAT activity when cells were maintained in 10% NBS than in 10% FCS. The level of induction was also dependent on the serum concentration. These data indicate that a serum component, possibly a cytokine(s), can enhance the UV response of both irradiated cells and unirradiated cells cocultivated with irradiated cells. The magnitude of UV responsiveness seemed also to be strain dependent. CAT activity for the HIV LTR promoter from the HTLV-IIIB (HIV-IIIB) strain was induced more than 30-fold by UV irradiation whereas activity from the LAV-1BRU strain was less than 2-fold. In contrast, both constructs were strongly induced by Tat expression. This indicates that there are differences in the induction mechanism for these two stimuli, even though UV radiation has been previously reported to induce a cellular Tat-like factor (Valerie K, et al., Nature [London] 1988;333:78-81).

Ultraviolet irradiation and cytokines as regulators of HIV latency and expression

The ability of the human immunodeficiency virus (HIV) to persist and replicate in human CD4+ T lymphocytes and mononuclear phagocytes is under the control of both virally encoded proteins and a variety of host-related factors. Ultraviolet (UV) light has been shown to induce transcription and expression of HIV. Both DNA damage and repair and DNA damage/repair-independent pathways caused by UV irradiation lead to expression of proviral HIV genomes via activation of the cellular transcription factor NF-kappa B. Transgenic mice that contain either long terminal repeat (LTR)-reporter genes or HIV genomes, either full length or deleted in the gag-pol region, express RNA and proteins at the epidermal level, particularly after UV irradiation. Furthermore, UV-triggered release of soluble factors capable of inducing expression of HIV in non-irradiated cells has been observed. Among other host factors, the functional network of pro-inflammatory and immunoregulatory cytokines has been demonstrated to act as a potent regulator of HIV replication, at least in different in vitro systems of infection.