Endotoxin-responsive sequences control cachectin/tumor necrosis factor biosynthesis at the translational level

The Rev protein of human immunodeficiency virus type 1 counteracts the effect of an AU-rich negative element in the human papillomavirus type 1 late 3' untranslated region

We have identified a sequence in the late 3' untranslated region of human papillomavirus type 1 mRNAs that acts posttranscriptionally to repress gene expression. Deletion analysis localized the inhibitory element to an AU-rich sequence between nucleotides 6958 and 6984 on the human papillomavirus type 1 genome. This sequence inhibits gene expression in an orientation-dependent manner. Upon transfection of eucaryotic cells with plasmids containing this sequence, approximately 4-fold-lower cytoplasmic mRNA levels and 64- to 128-fold-lower protein levels were produced compared with those produced by plasmids lacking the inhibitory sequence. Interestingly, providing the constitutive transport element of simian retrovirus type 1 in sense orientation counteracted inhibition exerted by the human papillomavirus type 1 sequence. Inhibition could also be overcome by the presence of human immunodeficiency virus type 1 Rev protein in trans and its target sequence, the Rev-responsive element, in cis. Rev is a nuclear protein and acts by promoting nuclear export of human immunodeficiency virus type 1 mRNAs encoding structural proteins. Our results are consistent with a model for human papillomavirus type 1 late-gene expression in which mRNAs containing human papillomavirus type 1 inhibitory sequences enter a nonproductive route in the nucleus, resulting in inefficient mRNA utilization. Rev directs mRNA containing inhibitory sequences to a productive route by interacting with the Rev-responsive element.

The effects of oxidized low density lipoproteins on inducible mouse macrophage gene expression are gene and stimulus dependent

Oxidized LDL has been previously reported to suppress the expression of genes induced in mononuclear phagocytes by inflammatory stimuli. In this study we extend these findings to demonstrate that the suppressive effects of oxidized LDL vary depending upon the gene being monitored and the stimulus being used to induce or enhance its expression. The expression of a selection of LPS-inducible genes exhibited differential sensitivity to pretreatment with oxidized LDL. Furthermore, the ability of oxidized LDL to suppress gene expression varied markedly with the inducing stimulus used. TNF alpha and IP-10 mRNA expression induced by IFN gamma and IL-2 was markedly more sensitive to suppression by oxidized LDL than that induced by LPS. The cooperative effects of IFN gamma and LPS on the expression of the inducible nitric oxide synthase gene were suppressed by oxidized LDL while the antagonistic effect of IFN gamma on LPS-induced expression of the TNF receptor type II mRNA was not altered. The suppressive activity of LDL was acquired only after extensive oxidation and was localized in the extractable lipid component. These results suggest a potent and direct connection between the oxidative modification of LDL and the chronic inflammation seen in atherogenic lesions. Furthermore, the appreciable selectivity of oxidized LDL in mediating secondary control of cytokine gene expression demonstrates that the active material(s) is targeted to disrupt specific intracellular signaling pathways.

Expression of leukemia inhibitory factor and interleukin-11 by human melanoma cell lines: LIF, IL-6, and IL-11 are not coregulated

Dysregulation in cytokines has been associated with melanomas. For example, loss of growth inhibition in advanced melanomas has been associated with interleukin-6 (IL-6) expression. Because IL-6 belongs to the hematopoietic cytokine family, which includes leukemia inhibitory factor (LIF) and interleukin-11 (IL-11), we examined the possibility of coordinate expression of LIF, IL-6, and IL-11 in three human melanoma cell lines derived from primary lesions (early) and in four lines derived from metastatic tumors (advanced). All lines examined produced at least low levels of LIF and IL-11 mRNA as measured by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). By enzyme-linked immunosorbent assay (ELISA), two of three early and three of four advanced lines were found to secrete LIF protein. IL-11 was assayed using growth of the responsive B9/11 cell line, but only one of seven lines made a low but measurable amount of IL-11. Cytokine protein production was not strictly correlated with mRNA abundance, nor was it strongly correlated with tumor staging. Recombinant LIF and IL-11 protein had no effect on the proliferation of any of the seven lines, suggesting that they do not act as autocrine growth factors for these melanomas. Assay of IL-6, IL-11, and LIF protein in conditioned medium from early and advanced melanoma lines gave no evidence of coordinate expression of these cytokines. We conclude that LIF and IL-11 production by melanomas may have some paracrine or endocrine function in the course of melanoma progression.

Prevention of autoimmune demyelination in non-human primates by a cAMP-specific phosphodiesterase inhibitor

Experimental allergic encephalomyelitis (EAE) is an autoimmune disease of the central nervous system that serves as a model for the human disease multiple sclerosis. We evaluated rolipram, a type IV phosphodiesterase inhibitor, for its efficacy in preventing EAE in the common marmoset Callithrix jacchus. In a blinded experimental design, clinical signs of EAE developed within 17 days of immunization with human white matter in two placebo-treated animals but in none of three monkeys that received rolipram (10 mg/kg s.c. every other day) beginning 1 week after immunization. In controls, signs of EAE were associated with development of cerebrospinal fluid pleocytosis and cerebral MRI abnormalities. In the treatment group, there was sustained protection from clinical EAE, transient cerebrospinal fluid pleocytosis in only one of three animals, no MRI abnormality, and marked reduction in histopathologic findings. Rolipram-treated and control animals equally developed circulating antibodies to myelin basic protein. Thus, inhibition of type IV phosphodiesterase, initiated after sensitization to central nervous system antigens, protected against autoimmune demyelinating disease.

Human CuZn superoxide dismutase enzymatic activity in cells is regulated by the length of the mRNA

Single functional human CuZnSOD gene encodes two species of mRNA differing in size by 200 nucleotides in the 3'-untranslated region (UTR). We studied the expression of the CuZnSOD cDNA with different 3'- and 5'-UTR. Deletion in the 5'-end does not affect the expression of the enzyme, however, deletion in the 3'-UTR decreases the level of expression of CuZnSOD. The plasmids containing the long CuZnSOD cDNA with all polyadenylation signal sequences utilize primarily the last polyadenylation site and give a long mRNA, which produces three times more enzyme than the short mRNA lacking the last polyadenylation site and the AU-rich region.

Differential expression of IL-1 beta, TNF-alpha, IL-6, and IL-8 in human monocytes in response to lipopolysaccharides from different microbes

Macrophages respond to bacterial lipopolysaccharides (LPS) and activate several host defense functions through production of mediators. However, it is not clear whether the degree of macrophage responsiveness to different sources of LPS is equivalent to or varies with the source of LPS. Therefore, in this report, we examined the extent of the human monocyte response to LPS derived from two oral pathogens, Actinobacillus actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg). Additionally, due to its well-established ability to activate monocytes, we used LPS from Escherichia coli (Ec). Human monocytes, when activated with a specific source of LPS, exhibited rapid expression of mRNA for IL-1 beta, TNF-alpha, and IL-8, which was followed by IL-6, as measured by RNA-PCR. Moreover, the expression of mRNA for these cytokines was followed by cytokine synthesis. Monocytes from the same subject, when activated with LPS from Pg, Aa, or Ec expressed quantitatively different levels of mRNA and proteins for all four cytokines. A given LPS induced either high or low expression of the battery of cytokines tested, indicating that the expression of these pro-inflammatory cytokines may be regulated by a single or a cluster of gene(s). However, no apparent differences in the time course of mRNA expression for these cytokines were observed in response to any of the LPS tested. Furthermore, the relative ability of the different sources of LPS to induce mRNA for cytokines varied throughout a wide range of LPS concentrations. This suggests that differences exist in the sensitivity of monocytes to a specific LPS, rather than in the kinetics of the secretory process itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the human TNF promoter by the transcription factor Ets

Tumor necrosis factor (TNF) affects the growth, differentiation, and function of a multitude of cell types and is viewed as a potent mediator of inflammation and cellular immune responses. In order to delineate functional domains that control TNF gene transcription, we have analyzed a 5' flanking region of the human TNF promoter spanning base pairs -115 to -98. This region contains a PEA3/Ets-1 binding motif 5' GAGGA 3' in direct juxtaposition to an AP-1/ATF-like palindromic sequence motif 5' TGAGCTCA 3'. Specific binding of Ets and Jun to their respective elements is demonstrated by competition analysis as well as by supershift assays. As shown by promoter deletion analysis, these two binding sites were essential for both basal promoter activity and responsiveness to the phorbol ester phorbol 12-myristate 13-acetate. Co-transfection of c-ets or c-jun expression plasmids along with TNF promoter-CAT reporter constructs revealed the participation of both transcription factors in the regulation of TNF gene transcription. Correspondingly, site-specific mutation of either Ets or Jun sites led to a complete loss of responsiveness to the respective transcription factor. These data suggest an essential role of Ets for the activation of TNF gene transcription.

Interleukin-4 inhibits the expression of tumour necrosis factors alpha and beta, interleukins-1 beta and -6 and interferon-gamma

T cell-derived IL-4 inhibits the expression of several inflammatory cytokine genes. In this study, IL-4 downregulated TNF-alpha and -beta, IL-1 beta IL-6 and IFN-gamma steady-state mRNA and protein production by blood leukocytes. In a detailed kinetic analysis, cytokine mRNA levels were significantly decreased in the presence of IL-4, suggesting an early and prolonged downregulatory effect. These findings support the general thesis that IL-4 is an important regulator of the inflammatory immune response.

A protein kinase involved in the regulation of inflammatory cytokine biosynthesis

Production of interleukin-1 and tumour necrosis factor from stimulated human monocytes is inhibited by a new series of pyridinyl-imidazole compounds. Using radiolabelled and radio-photoaffinity-labelled chemical probes, the target of these compounds was identified as a pair of closely related mitogen-activated protein kinase homologues, termed CSBPs. Binding of the pyridinyl-imidazole compounds inhibited CSBP kinase activity and could be directly correlated with their ability to inhibit cytokine production, suggesting that the CSBPs are critical for cytokine production.

Production of salmon calcitonin I in Oncorhynchus gorbuscha by alternative polyadenylation of two RNA species

RNAs of ultimobranchial bodies (U.B.) from the pink salmon, Oncorhynchus gorbuscha, were studied using the polymerase chain reaction (PCR) with specific oligodeoxyribonucleotides (oligos) of the salmon calcitonin (sCT) mRNA selected in exon 2 or 3 and a poly(T) oligo. We observed two amplified DNA fragments, differing by 200 bp which hybridized with a specific exon 4 probe. Sequence analysis indicated that they both encoded exon 4, but differed in the length of their 3' non-coding regions by use of a putative polyadenylation signal situated 200 bp upstream from the established polyadenylation site. These two polyadenylation signals very likely were regulated differently, as the larger expressed transcript was predominant. To date, such use of an alternative polyadenylation signal in a CT mRNA has not been described in other vertebrates, and only the chicken CT mRNA possesses a second classical polyadenylation signal which is not known to be used. This characteristic of sCT biosynthesis appears to be typical in lower vertebrates and is of phylogenic interest. Moreover, it engenders a hypothesis of a relationship between the high concentration of the peptide observed in females of this species and their capacity to produce sCT by different biosynthetic pathways.

Lipopolysaccharide signals activation of tumor necrosis factor biosynthesis through the ras/raf-1/MEK/MAPK pathway

BACKGROUND

Lipopolysaccharide (LPS) is known to activate macrophages, causing the release of toxic cytokines that may provoke inflammation and shock. One of the most important and best studied of these cytokines is tumor necrosis factor (TNF). Details of the signaling pathway leading to TNF biosynthesis remain unclear. The pathway is branched in the sense that TNF gene transcription and TNF mRNA translation are both strongly stimulated by LPS. Recent evidence has indicated that MAP kinase homologs become phosphorylated in LPS-stimulated cells, suggesting their possible involvement in signal transduction. We sought to test this hypothesis.

MATERIALS AND METHODS

Measurements of LPS-induced MEK and ERK2 activity were undertaken in LPS-sensitive and LPS-insensitive cells. Transfection studies, in which dominant inhibitors of ras and raf-1 were used to block signaling to the level of MAP kinase, were carried out in order to judge whether the TNF gene transcription and TNF mRNA translation are modulated through this pathway.

RESULTS

In RAW 264.7 mouse macrophages, both ERK2 and MEK1 activity are induced by LPS treatment. In the same cell line, dominant negative inhibitors of ras and raf-1 block LPS-induced activation of the TNF promoter, as well as derepression of the translational blockade normally imposed by the TNF 3'-untranslated region. A constitutively active form of raf-1 (raf-BXB) was found to augment, but not replace, the LPS signal. In LPS-insensitive cells (RAW 264.7 x NIH 3T3 fusion hybrid cells and primary macrophages derived from C3H/HeJ mice), ERK2 activity was found to be refractory to induction by LPS.

CONCLUSIONS

The ras/raf-1/MEK/MAPK pathway is chiefly responsible for transduction of the LPS signal to the level of the TNF gene and mRNA. raf and raf-1 lie upstream from (or actually represent) the physical branchpoints of the transcriptional and translation activation signals generated by LPS. The lesions that prevent LPS signaling in macrophages from C3H/HeJ mice, or in RAW 264.7 x NIH 3T3 fusion hybrid cells, occupy a proximal position in the signaling pathway.

Silica increases tumor necrosis factor (TNF) production, in part, by upregulating the TNF promoter

Silica causes release of tumor necrosis factor (TNF) from mononuclear phagocytes. One hypothesis is that silica increases TNF production, in part, by upregulating the TNF gene. To evaluate this hypothesis, THP-1 cells (a myelomonocytic cell line) were exposed to various amounts of silica and then the TNF gene transcription was evaluated. In this study silica caused a dose-dependent increase in TNF mRNA and the peak response occurred at 3 h following stimulation. A transient transfection assay also showed that silica upregulated expression of a TNF CAT construct in THP-1 cells. Furthermore, a nuclear run-on assay demonstrated that silica particles induce increased TNF gene transcription in exposed cells. THP-1 cells cultured for various periods of time in the presence of silica released TNF into the cell supernatants. These studies show that silica can upregulate the TNF gene, which results in the release of TNF protein from the cells.

Characterization of an Krox-24/Egr-1-responsive element in the human tumor necrosis factor promoter

We have analyzed in various human leukemic cell lines a previously unrecognized region within the human TNF gene promoter that contains the sequence motif 5'-CCGCCCCCGCG-3'. This GC-rich sequence maps to bps -170 and -160 of the TNF gene. Electrophoretic mobility shift assays (EMSA) combined with methylation interference analysis revealed the binding of two distinct proteins with overlapping recognition sites. Supershift assays identified the constitutive transcription factor Sp1 and the immediate-early growth-response transcription factor Egr-1/Krox-24. Interestingly, this Egr-1-related factor was induced by PMA but not by TNF. The TNF gene GC-rich sequence conferred PMA responsiveness when linked to a heterologous minimal c-fos promoter. To examine the involvement of Egr-1/Krox-24 in TNF gene regulation, a Krox-24 expression vector was used, pSCTKr24. In Jurkat T cells pSCTKr24 stimulated pTNF-286CAT that contains sequences -286 to +34 of the human TNF gene fused to the chloramphenicol acetyltransferase (CAT) gene. Moreover, pSCTKr24 also stimulated the TNF gene GC-rich sequence linked to the minimal c-fos promoter. However, deletion of this site did not result in markedly reduced TNF promoter activity, suggesting that the Egr-1/Krox-24 response element may play an auxiliary role in TNF gene regulation.

Role of gamma interferon and tumor necrosis factor alpha during T-cell-independent and -dependent phases of Mycobacterium avium infection

To design an effective immunotherapy for Mycobacterium avium infections, the protective host response to the infection must be known. Here we analyzed the role of gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in the innate and acquired responses to M. avium infections in mice. T-cell depletion studies showed that CD4+ T cells were required for control of the infection. CD(4+)-depleted mice showed enhanced bacterial proliferation and at the same time showed a reduction in the level of expression of both IFN-gamma and TNF-alpha mRNAs in spleen cells. In contrast, M. bovis BCG immunization restricted M. avium proliferation and at the same time promoted expression of the mRNAs for the two cytokines. In vivo depletion studies using specific monoclonal antibodies showed that both IFN-gamma and TNF-alpha are involved in an early protection possibly involving NK cells, and furthermore, IFN-gamma is involved in the later T-cell-protective response to infection. In vivo neutralization of IFN-gamma during M. avium infection also blocked the priming for enhanced TNF-alpha secretion triggered by endotoxin. Both cytokines were found to be involved in the resistance expressed in BCG-immunized animals and exhibited additive bacteriostatic effects in vitro on bone marrow-derived macrophages infected with different strains of M. avium. These data suggest that both cytokines act in an additive or synergistic fashion in the induction of bacteriostasis and that IFN-gamma is also involved in priming TNF-alpha secretion.

Regulation of macrophage gene expression by T-cell-derived lymphokines

Cytokines secreted from antigen-specific T lymphocytes provide important positive and negative control of inflammation through their effects on non-antigen-specific inflammatory leukocytes. These effects often involve modulation of gene expression. Lymphokine-inducible macrophage gene expression is largely controlled at the level of transcription. Multiple cis-acting sequence motifs cooperate with one another to produce patterns of expression that are relatively unique to individual genes. Members of trans-acting transcription factor families, which recognize related regulatory sequence elements, participate frequently in complex protein-protein interactions that generate remarkable complexity in terms of the number of potential combinations and the consequential functional differences exhibited by each combination. Thus, the remarkable plasticity of immune-mediated inflammation derives from combinations of finite numbers of options at several points in the cellular and molecular sequence.

Tumor necrosis factor-alpha expression in ischemic neurons

BACKGROUND AND PURPOSE

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine with diverse proinflammatory actions, including endothelial leukocyte adhesion molecule expression. Since leukocytes infiltrate into ischemic brain lesions, the present study was conducted to examine whether TNF-alpha messenger RNA (mRNA) and peptide are expressed in the brain after experimental focal stroke and before leukocyte accumulation.

METHODS

TNF-alpha mRNA and protein expression were monitored in the ischemic and nonischemic cerebral cortex of rats after focal ischemia produced by permanent middle cerebral artery occlusion. The effect of TNF-alpha administered by microinjection into the brain cortex on leukocyte adherence to brain capillaries was also studied.

RESULTS

Induction of TNF-alpha mRNA, normalized to a standard reference rat macrophage TNF-alpha mRNA, was detected as early as 1 hour after middle cerebral artery occlusion. TNF-alpha mRNA was elevated by 3 hours (29 +/- 6% versus 2 +/- 1% in sham-operated rats) only in the ischemic cortex, with peak expression at 12 hours (104 +/- 8%; P < .01). Five days after middle cerebral artery occlusion, TNF-alpha mRNA levels in ischemic cortex were still significantly elevated (38 +/- 5%; P < .05). Also, TNF-alpha mRNA expression was greater in the ischemic cortex of spontaneously hypertensive rats than in normotensive rats (P < .05). Double-labeling, immunohistochemical studies revealed the presence of TNF-alpha protein localized within nerve fibers in the evolving infarct at 6 and 12 hours after ischemia and further expression in the tissues immediately adjacent to the infarct 24 hours after ischemia. After 5 days, the neuronally localized peptide had diminished greatly, but macrophages located within the infarcted tissues were immunoreactive. Cortical microinjections of TNF-alpha (10 ng in 1 microL) produced a significant neutrophil adherence/accumulation in capillaries and small blood vessels 24 hours later.

CONCLUSIONS

These results represent the first demonstration that focal cerebral ischemia in rats results in elevated TNF-alpha mRNA and protein in ischemic neurons. The neuronal expression of peptide appears to facilitate the infiltration of inflammatory cells that can further exacerbate tissue damage in cerebral ischemia and might contribute to increased sensitivity and risk in focal stroke.

Developmentally regulated effects of lipopolysaccharide on biosynthesis of the third component of complement and factor B in human fibroblasts and monocytes

Developmental regulation of the effects of lipopolysaccharide (LPS) on complement protein biosynthesis was studied in human fibroblasts from fetuses, newborn infants and adults, and in human monocytes from newborn infants and adults, using RNA blot analysis and immunoprecipitation of metabolically radiolabelled cell lysates. The responsiveness of the third component of complement (C3) and factor B protein synthesis to LPS is limited by translational mechanisms in the newborn infant and by pretranslational mechanisms in the fetus. Translation of RNA from LPS-induced cells in a rabbit reticulocyte lysate cell-free translating system indicated no differences in specific translational activity between LPS-induced adult and neonatal RNA, suggesting that LPS-induced neonatal C3 and factor B transcripts are translationally competent, but lack either access to relevant protein synthetic pathways or co-factor(s) necessary for translation. Interferon-gamma (IFN-gamma) enhanced translational activity of LPS-induced C3 and factor B transcripts in neonatal cells, suggesting that lack of translation in these cells may be due to the absence of a necessary co-factor. Experiments with LPS and cycloheximide or LPS and interleukin-1 alpha (IL-1 alpha) suggested that a newly synthesized protein did not participate in translational regulation and that LPS induction did not alter translational activity of IL-1 alpha-induced C3 and factor B transcripts. We conclude that the responsiveness of C3 and factor B protein synthesis to LPS is regulated at developmentally unique and specific steps in gene expression.

Fertilization of Xenopus eggs imposes a complete translational arrest of mRNAs containing 3'UUAUUUAU elements

The early embryonic development of Xenopus is mainly governed by post-transcriptional regulations until the mid-blastula transition. In this report, we present evidence demonstrating that fertilization of Xenopus eggs triggers a complete translational arrest of mRNAs containing UA-rich elements in their 3'-untranslated region. This control is maintained at least until the mid-blastula transition. Neither maturation nor pseudo-fertilization of the egg is sufficient for triggering this control, suggesting that components originating from the male gamete are involved in the mechanism. Moreover, this control is exerted whether the mRNA is polyadenylated or not.

Storage of messenger RNA in eukaryotes: envelopment with protein, translational barrier at 5' side, or conformational masking by 3' side?

Messenger RNA can be stored in the cytoplasm of higher Eukaryotes in the form of masked messenger ribonucleoprotein particles (masked mRNPs, or informosomes). The typical example is the storage of mRNPs in germ cells (oocytes and spermatocytes). The masked mRNPs are inactive in translation, stable, i.e., protected against degradation, and unavailable for poly(A) tail processing, such as cytoplasmic polyadenylation and deadenylation. The major nonspecific mRNA-binding protein forming mRNPs and belonging to a special p50 family of basic, glycine-rich, phosphorylatable proteins seems to be necessary, but not sufficient for the masking. In some cases, mRNA-specific repressor proteins bound to the 5'-untranslated regions (5'-UTR) of mRNAs may be involved. Interactions of the 3'-untranslated regions (3'-UTR) with sequence-specific proteins seem to be of decisive importance for the masking of mRNPs. The hypothesis is proposed that the masking is achieved through a 3'-UTR-induced conformational rearrangement of mRNP; closing into a circle and condensation of mRNP are considered plausible.

Characterization of the immunogenetic basis of ultraviolet-B light effects on contact hypersensitivity induction

Ultraviolet-B (UVB) light has proven to be deleterious to the skin immune system in mice, and one major consequence is impairment of the induction of contact hypersensitivity (CH) to haptens applied to UVB-exposed skin. It has been shown recently that the damaging effects of UVB on CH are mediated primarily by tumour necrosis factor-alpha (TNF-alpha). Moreover, not all strains of mice are equally susceptible to the deleterious effects of UVB. Mice that develop CH when hapten is applied to UVB-exposed skin are termed UVB-resistant (UVB-R), whereas mice that fail to acquire CH under these circumstances are termed UVB-susceptible (UVB-S). In the present experiments, we have characterized the UVB-susceptibility of numerous, genetically disparate inbred strains of mice by applying dinitrofluorobenzene (DNFB) epicutaneously to normal and to UVB-exposed body wall skin. The results indicate that the intensities of CH responses of these different strains were distributed in a bimodal fashion, with means at 92% and 28.5% of positive control responses. Among the strains with CH values distributed around the higher mean (i.e. UVB-R mice), the intensity of CH responses after UVB irradiation was uniformly greater than 75% of the intensity found among their positive controls. By contrast, among the strains with CH values distributed around the lower mean (i.e. UVB-S mice), the intensity of CH responses after UVB exposure was uniformly less than 60% of the intensity displayed by their positive controls. The phenotypic traits of UVB-S and UVB-R appear, therefore, to be genetically determined. To that end, we provide in this report additional evidence that UVB-S is a polygenically determined trait that is dictated by polymorphisms at a locus within H-2, and at the Lps locus. Resistance to UVB radiation is a recessive trait, and requires homozygosity of resistance alleles at one or both of the two participating loci, whereas UVB-S acts as a dominant trait. Among H-2 congenic strains of mice that are lipopolysaccharide (LPS)-sensitive (Lpsn), UVB radiation impaired the induction of CH to DNFB in all mice except those of the H-2d and H-2a haplotypes. Thus, UVB-susceptibility is dictated by alleles at two, independent genetic loci that can influence transcriptional and translational activity of the Tnf-alpha gene. The potential biological and medical meaning of regulatory polymorphisms governing TNF-alpha production in the skin may be revealed by the recent demonstration that UVB-susceptibility and UVB-resistance are phenotypic traits in humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Evolutionary conservation of the AU-rich 3' untranslated region of messenger RNA

AU-rich sequence motifs (specifically sequences containing reiterations of AUUUA) are found in the 3' untranslated region of mammalian mRNAs encoding cytokines, adhesion molecules, and protooncogenes. Because these AU-rich elements (3'AURE) have been observed to reduce the stability and translational efficiency of transcripts that contain them, and because many of these transcripts accumulate in cells exposed to inflammatory stimuli, we reasoned that mRNAs with 3'AURE may be highly conserved and that the AURE is a marker of mRNAs that are inducible by environmental stressors. To test this hypothesis, we developed a polymerase chain reaction (PCR) strategy to isolate specifically mRNAs with 3'AURE. We first validated the effectiveness of this approach by selectively amplifying two mRNAs containing 3'AURE from interleukin 1 (IL-1)-induced human endothelial cells, then used the same primers in reverse transcriptase-PCR of sea urchin RNA, and used the radiolabeled reaction products to screen a cDNA library prepared from endotoxin-exposed sea urchin coelomocytes. We identified 124 positive clones and isolated a 1608-base-pair fragment that contains an AU-rich consensus sequence upstream from a poly(A) tail. This sea urchin transcript hybridizes with immobilized poly(A)(+)-selected RNA prepared from living coelomocytes maintained in vitro for 8.5-13 h but not with RNA prepared from freshly harvested coelomocytes. Our results provide support for the growing body of evidence that 3' AURE are both conserved and functional and indicate further that isolation and short-term in vitro culture of sea urchin coelomocytes is sufficient to induce the expression of transcripts containing 3'AURE.

Induction of cytokines in phagocytic mammalian cells infected with virulent and avirulent Listeria strains

The present paper analyzes the cytokine response of mouse macrophages during infection by Listeria monocytogenes. The use of different mutants of L. monocytogenes impaired in various steps of the infection process allowed us to dissect the cytokine response. Cytokine mRNA expression was detected by PCR-assisted amplification of RNA extracted from macrophages after infection with different Listeria strains. An increase in the amount of mRNA for tumor necrosis factor alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha), IL-1 beta, and IL-6 was detected in P388D1 macrophages infected with L. monocytogenes at 4 h postinfection. Interestingly, only hemolytic strains of L. monocytogenes were able to induce IL-1 alpha, IL-6, and TNF-alpha mRNA. This indicated that the induction of these cytokine mRNAs requires entry of the listeriae into the host cell cytoplasm. In contrast, IL-1 beta was also induced by infection with nonhemolytic mutants of L. monocytogenes which remain entrapped within the phagosome. The levels of TNF, IL-1 alpha, and IL-6 found in the supernatants of Listeria-infected P388D1 macrophages generally correlated well with the induction of the respective mRNAs, but it became obvious that cytokine activity is also regulated through posttranscriptional mechanisms. In vitro induction of the cytokines IL-1 alpha, IL-1 beta, IL-6, and TNF-alpha was also observed by infection of bone-marrow-derived macrophages with L. monocytogenes.

AU-A, an RNA-binding activity distinct from hnRNP A1, is selective for AUUUA repeats and shuttles between the nucleus and the cytoplasm

The 3'-untranslated regions of many labile transcripts contain AU-rich sequences that serve as cis determinants of mRNA stability and translational efficiency. Using a photocrosslinking technique, our laboratory has previously defined three cytoplasmic RNA-binding activities specific for the AUUUA multimers found in the 3'-untranslated regions of lymphokine mRNAs. One of these activities, AU-A, has an apparent molecular mass of 34 kDa, is constitutively expressed in both primary T cells and the Jurkat T cell leukemia line, and binds to a variety of U-rich RNA sequences. Previous studies had shown that AU-A is more prevalent in the nucleus than the cytoplasm, raising the possibility that AU-A is really a nuclear RNA-binding activity that is found in cytoplasmic extracts because of nuclear leakage during cell fractionation. We now show that AU-A shuttles between the cytoplasm and the nucleus. Our results indicate that AU-A is a candidate protein component of ribonucleoprotein complexes that participate in nucleocytoplasmic transport of mRNA and cytoplasmic mRNA metabolism. The properties of AU-A activity are similar to those of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). However, using monoclonal antibodies to hnRNP A1 and protease digestion patterns, we show that AU-A activity and hnRNP A1 protein are distinct. These studies have also allowed us to define a fourth RNA-binding activity of apparent molecular mass 41 kDa with specificity for AUUUA multimers. This activity is restricted to the nucleus and contains the hnRNP C protein.

A conserved stem-loop structure in the 3' untranslated region of procyclin mRNAs regulates expression in Trypanosoma brucei

African trypanosomes that cycle between mammalian hosts and the tsetse fly vector must be poised to survive in different environments. The control of stage-specific gene expression is undoubtedly one of the keys to successful adaptation, but no regulatory elements have been defined to date. Procyclins (also known as procyclic acidic repetitive proteins) are specifically expressed on the surface of procyclic and epimastigote forms in the fly. Procyclin genes are already transcribed in bloodstream forms, but stable mRNA, and later the protein, are first detected when the parasites begin to differentiate into procyclic forms. We have now identified a region of 16 bases that forms part of a predicted stem-loop structure in the 3' untranslated regions of different procyclin mRNAs; both the sequence and the secondary structure of this 16-mer appear to be required for efficient translation of a reporter gene in procyclic forms. The level of steady-state mRNA, its polyadenylylation, and its distribution in the cell are all unaffected by the presence or absence of this element. Deletion of the 16-mer alone reduces expression more than removal or reversal of the entire 3' untranslated region and flanking region, suggesting that there are additional negative regulatory elements in the same 3' untranslated region.

Translational control of cytokine expression by 3' UA-rich sequences

Several messenger RNAs which are transiently expressed contain a conserved uridine-adenosine-rich sequence in their 3' untranslated region. Many of these mRNas encode cytokines, growth factors or oncoproteins. This UA-rich sequence is composed of several interpsersed repeats of the octanucleotide UUAUUUAU and plays a key role in the post-transcriptional regulation of these mRNAs. Known as instability determinants, these UA-rich elements can also strongly affect mRNA translational efficiency. In this report, we review the data which illustrate this translational regulation and give insight the underlying mechanism.

Analysis of tumor necrosis factor promoter responses to ultraviolet light

Ultraviolet (UV) light induces the biosynthesis of chloramphenicol acetyltransferase (CAT) in the skin of mice bearing the CATTNF reporter transgene. Moreover, nuclear run-on assays indicate that UV light induces transcription of the TNF gene in RAW 264.7 macrophages. These observations suggest that the TNF gene (and/or its mRNA product) responds to signals elicited by UV light. To identify transcriptional UV response elements within the TNF promoter, and to determine whether a posttranscriptional response might also exist, a series of reporter constructs using a CAT coding sequence attached to various portions of the TNF promoter and 3' untranslated region were devised and transfected into several cultured cell lines. All cells tested were found to be UV responsive, and in NIH 3T3 cells, induction was found to depend upon two general regions of the promoter. The more distal region encompassed nucleotides (nt) -1059 through -451 with respect to the cap site, while the more proximal region spanned nt -403 through -261. A negative element, blocking the UV response, was interposed (nt -451 through -403). As with the response to LPS, the response to UV irradiation appears to involve translational activation in macrophages. However, the UV and LPS signaling pathways have little in common with one another, as indicated by three observations. First, no difference in responsiveness was observed on comparison of TNF gene induction in macrophages derived from C3H/HeN as opposed to C3H/HeJ mice. Second, cell fusion studies showed that while the LPS signaling pathway is extinguished by fusion of RAW 264.7 cells with NIH 3T3 cells, the UV signaling pathway remained intact. Finally, induction did not depend upon the NF-kappa B binding sites that are known to be required for LPS response in macrophages, since mutation of these sites did not impair the UV response.

C/EBP, NF-kappa B, and c-Ets family members and transcriptional regulation of the cell-specific and inducible macrophage inflammatory protein 1 alpha immediate-early gene

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) cytokine gene expression is restricted to a limited number of cells of hemopoietic origin and is rapidly and transiently induced by serum and endotoxin in macrophages. A single nuclear DNase I-hypersensitive site, which maps to the proximal promoter of the MIP-1 alpha gene, was identified in macrophage cells but was absent in cells which do not express basal levels of MIP-1 alpha mRNA. The proximal promoter sequences (+36 to -220 bp) are sufficient to confer cell-specific and inducible transcription in transfection assays. In vitro DNA-binding studies revealed five major nuclear protein binding sites in the proximal promoter which bind C/EBP, NF-kappa B, and/or c-Ets family members. Cell-specific differences in DNA binding by members of the NF-kappa B and c-Ets families correlate with the cell-specificity of MIP-1 alpha gene expression and the chromosomal conformation of the promoter. Changes in promoter binding by members of the C/EBP and NF-kappa B families correlate with the transcriptional up-regulation observed in serum- or endotoxin-stimulated macrophages in functional studies.

C/EBP, NF-kappa B, and c-Ets family members and transcriptional regulation of the cell-specific and inducible macrophage inflammatory protein 1 alpha immediate-early gene

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) cytokine gene expression is restricted to a limited number of cells of hemopoietic origin and is rapidly and transiently induced by serum and endotoxin in macrophages. A single nuclear DNase I-hypersensitive site, which maps to the proximal promoter of the MIP-1 alpha gene, was identified in macrophage cells but was absent in cells which do not express basal levels of MIP-1 alpha mRNA. The proximal promoter sequences (+36 to -220 bp) are sufficient to confer cell-specific and inducible transcription in transfection assays. In vitro DNA-binding studies revealed five major nuclear protein binding sites in the proximal promoter which bind C/EBP, NF-kappa B, and/or c-Ets family members. Cell-specific differences in DNA binding by members of the NF-kappa B and c-Ets families correlate with the cell-specificity of MIP-1 alpha gene expression and the chromosomal conformation of the promoter. Changes in promoter binding by members of the C/EBP and NF-kappa B families correlate with the transcriptional up-regulation observed in serum- or endotoxin-stimulated macrophages in functional studies.

Polymorphism of the mouse TNF-alpha locus: sequence studies of the 3'-untranslated region and first intron

We have sequenced the 3'-untranslated region (3'-UTR) and first intron of six strains of Mus musculus, as well as M. spretus, M. castaneus, and M. shanghai. A marked degree of polymorphism was evident in the sequences, and among all of the strains, no two haplotypes were identical. Of particular note, insertional mutations modifying the 5'-TTATTTAT sequence in the 3'-UTR, which in its RNA form acts as a translational repressor, were observed in New Zealand White and M. spretus strains. The mutations that we have identified dictate several restriction-fragment length polymorphisms, which should be useful in following the tumor necrosis factor-encoding gene (TNF) in backcross analysis and in defining the ancestry of TNF in mice of indeterminate parentage. Moreover, the data provide a substrate for the future analysis of differences in the level of TNF expression by genetically distinct mice.

Disruption in the AU motif of the mouse TNF-alpha 3' UTR correlates with reduced TNF production by macrophages in vitro

Many cytokine mRNAs exhibit a conserved, AU-rich motif in the 3'-untranslated region (UTR) of the molecule. Such sequence elements have been implicated in the regulation of mRNA turnover and as potential translational regulators. We report on the identification of a 3 base pair insertion which disrupts the AU motif of the TNF-alpha gene in the NZW, B10.KPA44, SM/J and Mus spretus mice and an insertion of an 8 base pair sequence into the 3' AU motif of the IL-10 gene in the Mus Spretus mouse. The mutation in the AU motif of the TNF-alpha gene correlates with reduced production of this cytokine by peritoneal macrophages from these mouse strains.

Thalidomide exerts its inhibitory action on tumor necrosis factor alpha by enhancing mRNA degradation

We have examined the mechanism of thalidomide inhibition of lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-alpha) production and found that the drug enhances the degradation of TNF-alpha mRNA. Thus, the half-life of the molecule was reduced from approximately 30 to approximately 17 min in the presence of 50 micrograms/ml of thalidomide. Inhibition of TNF-alpha production was selective, as other LPS-induced monocyte cytokines were unaffected. Pentoxifylline and dexamethasone, two other inhibitors of TNF-alpha production, are known to exert their effects by means of different mechanisms, suggesting that the three agents inhibit TNF-alpha synthesis at distinct points of the cytokine biosynthetic pathway. These observations provide an explanation for the synergistic effects of these drugs. The selective inhibition of TNF-alpha production makes thalidomide an ideal candidate for the treatment of inflammatory conditions where TNF-alpha-induced toxicities are observed and where immunity must remain intact.

Dissociation of lipopolysaccharide (LPS)-inducible gene expression in murine macrophages pretreated with smooth LPS versus monophosphoryl lipid A

Lipopolysaccharide (LPS) and the nontoxic derivative of lipid A, monophosphoryl lipid A (MPL), were employed to assess the relationship between expression of LPS-inducible inflammatory genes and the induction of tolerance to LPS in murine macrophages. Both LPS and MPL induced expression (as assessed by increased steady-state mRNA levels) of a panel of seven "early" inflammatory genes including the tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta, type 2 TNF receptor (TNFR-2), IP-10, D3, D8, and D2 genes (the last four represent LPS-inducible early genes whose functions remain unknown). In addition, LPS and MPL were both capable of inducing tolerance to LPS. The two stimuli differed in the relative concentration required to induce various outcome measures, with LPS being 100- to 1,000-fold more potent on a mass concentration basis. Characterization of the tolerant state identified three distinct categories of responsiveness. Two genes (IP-10 and D8) exhibited strong desensitization in macrophages pretreated with tolerance-inducing concentrations of either LPS or MPL. In macrophages rendered tolerant by pretreatment with LPS or MPL, a second group of inducible mRNAs (TNF-alpha, interleukin-1 beta, and D3) showed moderate suppression of response to secondary stimulation by LPS. The third category of inducible genes (TNFR-2 and D2) showed increased expression in macrophages pretreated with tolerance-inducing concentrations of either LPS or MPL. All of the LPS-inducible genes examined exhibited modest superinduction with less than tolerance-inducing concentrations of either stimulus, suggesting a priming effect of these adjuvants at low concentration. The differential behavior of the members of this panel of endotoxin-responsive genes thus offers insight into molecular events associated with acquisition of transient tolerance to LPS.

Extinction of the tumor necrosis factor locus, and of genes encoding the lipopolysaccharide signaling pathway

The tumor necrosis factor (TNF-alpha or TNF) gene is activated by both lipopolysaccharide (LPS) and cycloheximide in RAW 264.7 macrophages, whereas neither stimulus activates the gene in 3T3 fibroblasts. Moreover, the pattern of CG methylation within the TNF gene is readily distinguishable in DNA derived from cells of these two types. These findings would suggest that the TNF gene has been rendered inaccessible to transcription in the 3T3 cell environment. When RAW 264.7 cells are fused with 3T3 cells, an immortal pentaploid hybrid results. In the hybrid cell, all three TNF genes contributed by the RAW 264.7 cell parent become highly methylated according to the pattern observed in the 3T3 cell parent. Permanently transfected chloramphenicol acetyl transferase (CAT) reporter constructs, bearing 2.2 kb of upstream sequence (including the entire TNF promoter and 5'-untranslated region [UTR]) as well as 1.0 kb of downstream sequence (including the entire TNF 3'-UTR and termination sequence), are accessible in both RAW 264.7 cells and 3T3 cells, but are silenced in transition from the RAW 264.7 cell to the hybrid cell environment. Moreover, the endotoxin signaling pathway is abrogated, as assessed by transient transfection of hybrid cells with LPS-responsive CAT reporter constructs. It would therefore appear that the fusion of 3T3 cells and RAW 264.7 cells activates a system that silences the TNF gene, as well as the LPS signaling pathway. This system may operate to determine TNF gene accessibility and LPS responsiveness in the course of cell differentiation. The DNA sequences targeted within the TNF gene are included in the CAT reporter construct; therefore, the silencing element has been circumscribed to a region of DNA 3.2 kb in length.

Tumor necrosis factor, its receptors and the connection with interleukin 1 and interleukin 6

Cytokines are important mediators of the effects observed after the administration of endotoxin. One of them, tumor necrosis factor, is particularly important since it plays a cardinal role in two major endotoxin activities: its antitumor effect and its capacity to induce a systemic inflammatory response syndrome. TNF exerts its activity on a wide variety of target cells by the triggering of two distinct receptor types. TNF-R55 and TNF-R75. They induce distinct intracellular signals but can have cooperative effects. So, their differential triggering or modulation may have clinically relevant consequences. Based upon observations in the mouse, where hTNF does not interact with the TNF-R75 while mTNF triggers both receptor types, we propose that both receptors need to be triggered to obtain lethality after the administration of TNF. Since human TNF has retained antitumor activity, esp. in combination with IFN-gamma, TNF-mutants that are selective agonists for the TNF-R55 might have a broader therapeutic margin. One such human TNF mutant was already shown to be as effective as the wild-type hTNF in a xenograft model. However, several sensitizing agents may mimic TNF-R75 triggering and so make TNF-R55 triggering a lethal challenge. The fact that two such agents, RU38486 and IL-1 have similar effects regarding their kinetics and their capacity to sensitize for the lethality- and IL-6-inducing effect of hTNF may give a hint regarding the mechanism of the sensitizing effect.

An allelic polymorphism within the human tumor necrosis factor alpha promoter region is strongly associated with HLA A1, B8, and DR3 alleles

The tumor necrosis factor (TNF) alpha gene lies within the class III region of the major histocompatibility complex (MHC), telomeric to the class II and centromeric to the class I region. We have recently described the first polymorphism within the human TNF-alpha locus. This is biallelic and lies within the promoter region. Frequency analysis of the TNF-alpha polymorphism, using the polymerase chain reaction and single-stranded conformational polymorphism, in HLA-typed individuals, reveals a very strong association between the uncommon TNF allele and HLA A1, B8, and DR3 alleles. This is the first association between TNF-alpha and other MHC alleles and raises the possibility that the uncommon TNF-alpha allele may contribute to the many autoimmune associations of the A1,B8,DR3 haplotype.

Down-regulation of tumor necrosis factor alpha activity by acute ethanol treatment in human peripheral blood monocytes

As the most commonly used drug that can modulate both metabolic and immune pathways, ethanol is evaluated in this report as a regulator of tumor necrosis factor alpha (TNF alpha) production in human peripheral blood monocytes (M phi) in combination with a variety of stimuli. While acute ethanol treatment did not induce TNF alpha in M phi, it was a potent down-regulator of M phi TNF alpha production whether induced by the combination of interferon-gamma plus muramyl dipeptide (MDP) (P < 0.001), lipopolysaccharide (LPS) alone (P < 0.01), or interferon-gamma plus LPS. Down-regulation of M phi TNF alpha by ethanol was dose dependent and statistically significant in the biologically relevant, 25-150 mM, ethanol concentration range. We also demonstrate that these ethanol concentrations did not affect M phi viability. TNF alpha down-regulation by ethanol was most effective when ethanol was administered 4 hr prior to MDP stimulation; however, it was also effective--though to a lesser extent--if it was added at the time of MDP stimulation. Furthermore, ethanol also down-regulated TNF alpha production of the in vivo preactivated M phi of trauma patients, which produce hyperelevated levels of TNF alpha. We have previously shown that the majority of posttrauma elevated M phi TNF alpha is produced by the M phi subpopulation expressing high-affinity type I Fc gamma receptors (Fc gamma RI). When the Fc gamma RI cross-linking-stimulated M phi subpopulation was treated with acute ethanol, TNF alpha production was suppressed again both in in vivo preactivated M phi of trauma patients and in M phi of normal controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Sunlight and skin-associated lymphoid tissues (SALT): if UVB is the trigger and TNF alpha is its mediator, what is the message?

The damaging effects on cutaneous immunity of low-dose ultraviolet B (UVB) radiation in sunlight are genetically determined in mice. Polymorphic alleles at the Tnf alpha and Lps loci dictate whether mice are UVB susceptible or resistant, i.e., develop contact hypersensitivity or not when hapten is painted on UVB-exposed skin. In mice, UVB susceptibility is mediated almost exclusively by tumor necrosis factor-alpha (TNF alpha). Circumstantial evidence implicates urocanic acid (UCA) in the stratum corneum as the photoreceptor for UVB, and recent results suggest that cis-UCA in turn instigates the intraepidermal accumulation of TNF alpha. It is hypothesized that TNF alpha interrupts the induction of contact hypersensitivity by preventing epidermal Langerhans cells from carrying hapten to the draining lymph node, where activation of naive, hapten-specific T cells must first occur. The phenotypic traits of UVB susceptibility (UVB-S) and UVB resistance (UVB-R) have now been documented in human beings, and the frequency of UVB-S is high (approximately 40-45%) in both Caucasians and individuals with deeply pigmented skin. Because the frequency of UVB-S is extremely high in patients with biopsy-proved basal and squamous cell skin cancer, this trait appears to be a risk factor for this disease. The unexpectedly high frequency of UVB-S in human beings, including black-skinned persons, implies that the trait is not perceived by evolutionary processes as deleterious. The possible selective advantages conferred by alleles that determine UVB-S are discussed with respect to cutaneous infections in which mortality and morbidity are primarily mediated by immunopathogenic processes.