Cyclic AMP--an intracellular second messenger for interleukin 1

Requirements for the induction of the interleukin-2 receptor complex in a human pre-T-cell line

Cell line PER-117 is a T-cell receptor negative human T-cell line that can be induced to express a functional interleukin-2 receptor (IL-2R). Recombinant interleukin-1 (IL-1) as well as certain combinations of inducer substances could be shown to stimulate the expression of the p55 (alpha)-chain of the IL-2R in PER-117 cells. The synergistic increases in IL-2R alpha expression were demonstrated at the cell surface as well as at the mRNA level. The results suggested that in PER-117 cells IL-1 appears to induce expression of the alpha-chain by pathways that are different to activation via protein kinase C (PKC), and that drug-induced cyclic AMP (cAMP) activation did not substitute for IL-1. We found that the regulation of mRNA for IL-2R beta (p75) differed significantly from that seen for IL-2R alpha. Moreover, the requirements for IL-2R alpha induction determined for this cell line differ from other human cell lines, which may reflect that there are distinct requirements for activation depending on the stage of differentiation and/or lineage of the cells. The PER-117 cell line provides a unique model to examine further the mechanism leading to induction of a functional IL-2R at an early stage of human T-cell differentiation.

Interleukin-1-mediated phospholipid breakdown and arachidonic acid release in human synovial cells

OBJECTIVE

Interleukin-1 (IL-1), an important mediator contributing to joint destruction in rheumatoid arthritis, is known to stimulate the release of arachidonic acid (AA) and prostaglandin E2 (PGE2) from adherent synoviocytes. To study the intracellular pathways involved in these functions, we stimulated cultures of human synovial cells with recombinant IL-1 beta.

METHODS

AA liberation was measured after labeling synovial cells with 3H-AA, and PGE2 levels were determined by high performance liquid chromatography or radioimmunoassay. Identification of 3H-AA-labeled phospholipids was performed by thin layer chromatography. Cell-associated phospholipase A2 (PLA2) enzymatic activity was determined by an assay with cell-free systems and exogenous substrates.

RESULTS

Stimulation of synovial cells with recombinant IL-1 beta induced a decrease in phosphatidylcholine (PC), phosphatidylinositol (PI), and phosphatidylethanolamine (PE), and a marked increase in cell-associated PLA2 activity as compared with controls. In the presence of either quinacrine, an inhibitor of PLA2 pathway activation, or neomycin, which binds to PI mono- and biphosphate thus blocking their degradation by phospholipases, AA and PGE2 secretion were reduced in a dose-dependent manner. Kinetic studies revealed that quinacrine had little blocking activity on the IL-1-mediated AA release after 1 hour of stimulation but completely abolished it after 5 or 8 hours. In contrast, neomycin exerted a partial but significant inhibitory effect from the first hour of stimulation onward. Addition of quinacrine was also demonstrated to abolish the IL-1-induced hydrolysis of PC and PE but not PI, indicating that PC and PE are the preferred substrates for PLA2 enzymatic activity in human synovial cells.

CONCLUSION

Our findings strongly suggest that AA and PGE2 production by IL-1-triggered synoviocytes are largely dependent upon PLA2-mediated hydrolysis of PC and PE and to a lesser extent upon the earlier degradation of PI.

Activation of the sphingomyelin signaling pathway in intact EL4 cells and in a cell-free system by IL-1 beta

The mechanism of interleukin-1 (IL-1) signaling is unknown. Tumor necrosis factor-alpha uses a signal transduction pathway that involves sphingomyelin hydrolysis to ceramide and stimulation of a ceramide-activated protein kinase. In intact EL4 thymoma cells, IL-1 beta similarly stimulated a rapid decrease of sphingomyelin and an elevation of ceramide, and enhanced ceramide-activated protein kinase activity. This cascade was also activated by IL-1 beta in a cell-free system, demonstrating tight coupling to the receptor. Exogenous sphingomyelinase, but not phospholipases A2, C, or D, in combination with phorbol ester replaced IL-1 beta to stimulate IL-2 secretion. Thus, IL-1 beta signals through the sphingomyelin pathway.

Interleukin-1 alpha gene expression and localization of interleukin-1 alpha protein during tumor promotion

Treatment of the dorsal epidermis of SENCAR mice with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a time- and dose-dependent stimulation of interleukin-1 alpha (IL-1 alpha) gene expression. Levels of IL-1 alpha mRNA were elevated as early as 15 min and peaked at 3-4 h after a single application of TPA (2 micrograms or 10 micrograms). IL-1 alpha gene expression increased in epidermal tissue isolated from SENCAR mice at 1, 3, 6, 10, 16, and 22 wk after a single treatment with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and subsequent twice-weekly application of 2 micrograms TPA. IL-1 alpha-immunoreactive protein was specifically localized within suprabasal keratinocytes in cutaneous tissue isolated from mice treated with DMBA-TPA for 1-22 wk and in nonproliferating cells located within papilloma tissue isolated from SENCAR mice at 22 wk after initiation and promotion. Basal cells within hyperplastic epidermis did not produce IL-1 alpha-immunoreactive protein. DMBA treatment alone did not induce IL-1 alpha gene expression. Injection of IL-1 alpha-specific antibodies (50 micrograms) into SENCAR mice via the tail vein 2 h before treatment with TPA (2 micrograms or 10 micrograms) significantly (P < 0.05) inhibited the skin thickening usually observed 24 h after treatment with TPA. Autoradiography studies showed that injection of anti-IL-1 alpha antibodies inhibited incorporation of [methyl-3H]thymidine by keratinocytes within the epidermis and by cells within hair follicles. It also inhibited neutrophil infiltration into the dermis, which usually results from topical application of TPA. These data suggest that IL-1 alpha is a pivotal cytokine produced by specific subpopulations of epidermal keratinocytes and that IL-1 alpha primarily regulates the epidermal proliferative response of a distinctly separate population of keratinocytes after topical exposure of murine epidermis to TPA and secondarily modulates neutrophil migration into the dermis. Consequently, manipulation of IL-1 alpha may be a way to attenuate or abrogate the cutaneous response to TPA by altering keratinocyte proliferation, the resultant hyperplasia, and a portion of the inflammatory response characterized by dermal infiltration of neutrophils.

Cytokines increase neutral endopeptidase activity in lung fibroblasts

Fibroblasts of the pulmonary interstitium are intimately involved in the response of the lung to inflammation as well as in repair of injured tissues. The response of fibroblasts within an inflammatory site appears to be directed, in part, by peptide mediators. Neutral endopeptidase (NEP), a metallopeptidase on the surface membrane of fibroblasts, can inactivate various vasoactive peptides, including kinins and tachykinins. Because lung fibroblasts both secrete cytokines and respond to mediators within the immediate environment, NEP might be regulated by locally generated cytokines. We found that several cytokines, including interleukin-1 alpha (IL-1), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor, interleukin-6, and granulocyte macrophage colony-stimulating factor, enhanced activity of NEP on the surface of intact fibroblasts. In contrast, cultured pleural mesothelial cells had much lower levels of NEP than fibroblasts, and the enzyme was not enhanced by either IL-1 or TNF-alpha. Further studies with IL-1 showed that the effect required at least 6 h of exposure to the cytokine and depended upon final cytokine concentration. Combinations of IL-1 with other cytokines increased NEP activity beyond that in cells treated with individual cytokines, but combinations had less than additive effects. Selected pharmacologic agents indicated that the mechanism involves second messenger pathways. The cytokine effect on NEP was attenuated by indomethacin, an inhibitor of cyclooxygenase, by N-[2-(methylamino) ethyl]-5-isoquinolinesulfonamide dihydrochloride, an inhibitor of protein kinase, and by adenosine 3',5' cyclic monophosphothionate, an analog of cyclic adenosine monophosphate (cAMP) that competitively inhibits the cAMP signal pathway. It was mimicked by dibutyryl cAMP and by forskolin, an activator of adenyl cyclase.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor and interleukin 1 inhibit parathyroid hormone-responsive adenylate cyclase in clonal osteoblast-like cells by down-regulating parathyroid hormone receptors

The effects of the monokines tumor necrosis factor alpha (TNF) and interleukin 1 (IL 1) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Recombinant TNF and IL 1 incubated with UMR-106 cells for 48 hr each produced concentration-dependent inhibition of PTH-sensitive adenylate cyclase, with maximal inhibition of PTH response (40% for TNF, 24% for IL 1) occurring at 10(-8) M of either monokine. Both monokines also decreased adenylate cyclase stimulation by the tumor-derived PTH-related protein (PTHrP). In contrast, TNF and IL 1 had little or no inhibitory effect on receptor-mediated stimulation of adenylate cyclase by isoproterenol and nonreceptor-mediated enzyme activation by cholera toxin and forskolin; both monokines increased prostaglandin E2 stimulation of adenylate cyclase. Binding of the radioiodinated agonist mono-[125I]-[Nle8,18, Tyr34]bPTH-(1-34)NH2 to UMR-106 cells in the presence of increasing concentrations of unlabeled [Nle8,18, Tyr34]bPTH-(1-34)NH2 revealed a decline in PTH receptor density (Bmax) without change in receptor binding affinity (dissociation constant, Kd) after treatment with TNF or IL 1. Pertussis toxin increased PTH-sensitive adenylate cyclase activity but did not attenuate monokine-induced inhibition of PTH response. In time course studies, brief (1 hr) exposure of cells to TNF or IL 1 during early culture was sufficient to decrease PTH response but only after exposed cells were subsequently allowed to grow for prolonged periods. Inhibition of PTH response by monokines was blocked by cycloheximide. The results indicate that TNF and IL 1 impair responsiveness to PTH (and PTHrP) by a time- and protein synthesis-dependent down-regulation of PTH receptors linked to adenylate cyclase.

Synovial protein kinase C and its apparent insensitivity to interleukin-1

Lapine synovial fibroblasts produce prostaglandin E2 (PGE2) and neutral metalloproteinases in response to phorbol 12-myristate 13-acetate (PMA), human recombinant interleukin-1 (hrIL-1) and, in an autocrine fashion, in response to partially purified preparations of their own cytokines known as cell-activating factors (CAF). Here we have examined the possible role of protein kinase C (PKC) in these responses. Whereas the 80-kDa substrate for PKC could not be detected in synovial fibroblasts, these cells contained a 35-kDa protein which fulfilled the criteria for qualifying as a specific substrate of PKC. Translocation assays based upon phosphorylation of the 35-kDa protein and Western blotting techniques allowed the movement of PKC from the cytosolic to the particulate fraction in response to PMA and CAF to be detected but not in response to 4 alpha-PMA or hrIL-1. Inhibitors of PKC suppressed synovial activation by PMA, partially blocked activation by CAF but had no effect on activation by hrIL-1. There thus appear to be PKC-dependent and PKC-independent routes to synovial cell activation. Our data suggest that IL-1 uses the latter, while CAF contains cytokines which utilize both routes.

Selective nuclear transport of the Drosophila morphogen dorsal can be established by a signaling pathway involving the transmembrane protein Toll and protein kinase A

Establishment of dorsal-ventral polarity in the early Drosophila embryo requires a concentration gradient of the maternal morphogen dorsal (dl). This concentration gradient is established by selective nuclear transport of dl so that dl protein is present only in ventral nuclei. The activity of 11 genes is required for dl nuclear localization. One of these genes, Toll, encodes a transmembrane protein that appears to play the most direct role in regulating dl localization. We have examined the effects of Toll on dl in cotransfected Schneider cells to gain insight into the nature of the interaction between these proteins. We have found that Toll can enhance the nuclear localization of dl and, independently, the ability of dl to activate transcription once in the nucleus. We present evidence that the signaling pathway from Toll to dl involves protein kinase A (PKA) and that nuclear transport and activation of dl results from phosphorylation of dl by PKA. We discuss the significance of these results with respect both to Drosophila embryogenesis and to the regulation of the mammalian transcription factor NF-kappa B.

15-deoxyspergualin treatment of graft rejection in man: effect on mononuclear cells

We studied the effects of 15-deoxyspergualin (DSG) on human mononuclear cells in blood when DSG was administered as anti-rejection treatment to kidney-transplant patients in combination with methylprednisolone (MP) in a safety study. The numbers of leucocytes, lymphocytes and monocytes, the percentages of T and B cells and the expression of the interleukin 2 receptor and the human leucocyte antigen DR locus (HLA-DR) were determined in blood from these patients and from patients treated with MP only. We found that the number of lymphocytes and monocytes decreased in all groups, as also did the CD4/CD8 ratio and the HLA-DR expression on monocytes. DSG counteracted the increase in the number of leucocytes observed in patients treated with MP only. Different effects of DSG and MP were also observed on B cells. While the percentage of CD20+ cells increased in the MP group, it remained unaltered in patients given low-dose DSG and/or was decreased in those given higher doses. Since available evidence suggests an effect of DSG on B-cell reactivity, this drug may become an important addition to the arsenal of immunosuppressive drugs in clinical transplantation.

Cytokine regulation of adenylate cyclase activity in LLC-PK1 cells

Although several cytokines have been demonstrated to exert pleiotropic responses, there is little information on cytokine regulation of renal tubular epithelial cell function. In the present studies, we find that both T cell-derived (tumor necrosis factor-beta and interleukins 2 and 3) and monocyte/macrophage derived (tumor necrosis factor alpha and interleukin 1 beta) cytokines promote basal, arginine vasopressin- and forskolin-stimulated adenylate cyclase activity in cultured LLC-PK1 cells. No effect of TNF, IL-1 beta, and IL-2 to stimulate protein kinase C activity was observed. TNF-beta, IL-1 beta and IL-2 also modestly stimulated 3H release from 3H-arachidonic acid labeled cells. Mepacrine, a phospholipase A inhibitor, prevented TNF-beta stimulation of 3H release from 3H-arachidonic acid labeled cells and TNF-beta potentiation of adenylate cyclase activity. TNF-beta potentiation of adenylate cyclase activity and stimulation of 3H release from 3H arachidonic acid labeled cells was not prevented by pertussis toxin. These results demonstrate that several cytokines can stimulate adenylate cyclase activity while not affecting protein kinase C activity in cultured renal tubular epithelial cells. The effect of TNF-beta to stimulate adenylate cyclase appears to occur independent of pertussis toxin-sensitive substrate and may involve activation of phospholipase A.

Interleukin 1 and tumor necrosis factor-alpha stimulate the production of colony-stimulating factor 1 by murine astrocytes

Astrocytes have the ability to secrete colony-stimulating factor 1 (CSF-1), a growth factor known to stimulate the proliferation of brain macrophages. We have studied the effect of cytokines such as interleukin 1 (IL-1), tumor necrosis factor-alpha (TNF alpha), and interleukin 6 (IL-6) on the production of CSF-1 by cultured primary astrocytes and an astrocytic cell line derived from embryonic mouse brain. We observed that both TNF alpha and IL-1 increased CSF-1 mRNA and protein levels in the astrocytic cultures. In contrast, IL-6 was ineffective. The CSF-1 mRNA levels were strongly reduced by incubating immortalized astrocytic cells with staurosporine, a protein kinase C inhibitor, both in the absence and in the presence of cytokines. Conversely, 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C activator, increased CSF-1 mRNA levels. These results suggest a mechanism whereby mononuclear phagocytes could favor their own recruitment in the CNS by producing cytokines.

Interleukin-1 induces c-fos and c-jun gene expression in T helper type II cells through different signal transmission pathways

Interleukin (IL)-1 induces proliferation and expression of several protooncogenes in the T helper 2 cell line D10A. We have analyzed the signal transmission pathways activated by IL-1 in these cells, leading to the expression of c-jun and c-fos. IL-1 induced c-jun gene transcription and mRNA expression by means of a pathway dependent on protein tyrosine kinase activity since tyrphostin, a specific inhibitor of tyrosine kinase, inhibited this induction. This mechanism of transmission signaling was independent of protein kinase C (PKC) and was linked to the 80-kDa IL-1 receptor (IL-1R). In addition, phorbol esters did not induce c-jun mRNA expression, whereas c-fos mRNA expression mediated by IL-1 dependent on PKC; this pathway was linked to a different, still unidentified IL-1R that was functional in the D10A cell line. Accumulation of intracellular cAMP generated by IL-1 through the 80-kDa IL-1R negatively regulated c-fos expression which was induced by IL-1 through PKC activation. We conclude that IL-1 modulates the expression of c-fos in D10A cells by occupying of two independent IL-1R that are linked to different signal transduction pathways.

On the signal transducing mechanisms involved in the synergistic interaction between interleukin-1 and bradykinin on prostaglandin biosynthesis in human gingival fibroblasts

Recombinant human interleukin-1 beta (IL-1 beta) and bradykinin (BK) synergistically stimulate prostaglandin E2 (PGE2) formation in human gingival fibroblasts cultured for 24 h. Neither BK or IL-1 beta per se, nor their combinations, caused any acute stimulation of cellular cyclic AMP accumulation. BK, but not IL-1 beta, caused a rapid, transient rise of intracellular Ca2+ concentration ([Ca2+]i), as assessed by recordings of fura-2 fluorescence in monolayers of prelabelled gingival fibroblasts. IL-1 beta did not change the effect of BK on [Ca2+]i. Ionomycin and A23187, two calcium ionophores, synergistically potentiated the stimulatory effect of IL-1 beta on PGE2 formation. Three different phorbol esters known to activate protein kinase C also synergistically potentiated the action of IL-1 beta on PGE2 formation. Exogenously added arachidonic acid significantly enhanced the basal formation of PGE2. In IL-1 beta treated cells, the enhancement of PGE2 formation seen after addition of arachidonic acid, was synergistically upregulated by IL-1 beta. These data show that i) the synergistic interaction between IL-1 beta and BK on PGE2 formation is not due to an effect linked to an upregulation of cyclic AMP or [Ca2+]i; ii) the signal transducing mechanism by which BK interacts with IL-1 beta, however, may be linked to a BK induced stimulation of [Ca2+]i and/or protein kinase C; iii) the mechanism involved in the action of IL-1 beta may, at least partly, be due to enhancement of the biosynthesis of prostanoids mediated by an upregulation of cyclooxygenase activity.

Interleukin-1 beta induction of TNF-alpha gene expression: involvement of protein kinase C

In the human astroglioma cell line CH235-MG, interleukin-1 beta (IL-1 beta) induces transcriptional activation of the tumor necrosis factor-alpha (TNF-alpha) gene, resulting in expression of TNF-alpha mRNA and biologically active TNF-alpha protein. This study was undertaken to elucidate intracellular signaling pathways involved in IL-1 beta induction of the TNF-alpha gene. We demonstrated that the protein kinase C (PKC) activator 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) in concert with Ca++ ionophore A23187 induced expression of TNF-alpha mRNA and protein, whereas an inactive PMA analogue (alpha PMA) had no effect. Various cyclic nucleotide activators such as 8-Bromo cAMP, cholera toxin, and forskolin had no effect on TNF-alpha production. Two PKC inhibitors, H7 and staurosporine (SS), abrogated IL-1 beta induced TNF-alpha expression in a dose-dependent fashion. Treatment of CH235-MG cells with a high concentration of PMA (1 microM) for an extended period of time (48 h) caused a greater than 90% reduction in total PKC activity. Further strengthening a role for PKC in this cytokine response is the fact that IL-1 beta was no longer able to induce TNF-alpha expression in these PKC depleted cells. Last, IL-1 beta treatment produced an increase of total PKC activity in CH235-MG cells. Taken together, these data demonstrate that IL-1 beta induces TNF-alpha gene expression in CH235-MG cells in a PKC-dependent manner.

p21ras contributes to HIV-1 activation in T-cells

Activation of T-cells infected by HIV-1 results in activation of long terminal repeat (LTR)-dependent viral transcription and ultimately the production of infectious virus. Although full T-cell activation requires a complex series of intracellular signals, including protein kinase C activation, calcium mobilisation, and less-well defined lymphokine-induced signals, the HIV-1 LTR can be activated by subsets of these signals. We have studied the interaction of these signals in the human lymphoma line, Jurkat, in activation of the HIV-1 LTR. The HIV promoter was induced by IL-1 and phorbol ester activation of PKC but not by a calcium ionophore. The constitutively active form of Ha-ras could replace phorbol ester stimulation of the HIV promoter and of a synthetic promoter containing NF kappa B binding sites.

Interleukin-1 induces protein tyrosine phosphorylation in T cells

Interleukin (IL)-1 alpha activates multiple signal transmission pathways in the T helper type 2 cell line, D10A, and these pathways are linked to two separate IL-1 receptors (IL-1R). In the present report we show that IL-1 induces the activation of tyrosine kinase in these cells, leading to tyrosine phosphorylation of a subset of proteins of 38, 75, 97 and 115 kDa. This type of phosphorylation is prevented by a monoclonal antibody directed against the 80-kDa IL-1R and by tyrphostins which are specific inhibitors of tyrosine kinases. In addition, this inhibitor blocks IL-1-and IL-2-induced proliferation in D10A cells as well as the c-myc and c-myb proto-oncogene mRNA expression in response to IL-1. Interestingly, the inhibitor of cAMP-dependent kinase, H-8, only blocks IL-1-induced c-myb, but not c-myc mRNA expression. Altogether, our results demonstrate that the activation of a tyrosine kinase(s) is an early and major event that happens after IL-1/IL-1R interaction, leading to an increase in intracellular cAMP which results in c-myb and IL-5 mRNA expression. Independent of cAMP, by tyrosine phosphorylation of specific substrates IL-1 also induces c-myc and IL-6 mRNA expression and cellular proliferation.

Intracellular signal transduction in proliferation of synovial cells

We investigated some steps in the signal transduction pathway leading to the proliferation of synovial cells. 12-o-tetradecanoyl phorbol-13-acetate (TPA) which is known to stimulate phospholipid- and Ca(2+)-dependent protein kinase (C-kinase) enhanced the proliferation of synovial cells. The proliferation of synovial cells induced by interleukin-1 beta. Tumour necrosis factor alpha and granulocytes/macrophages colony stimulating factor, was inhibited by a potent C-kinase inhibitor, H7. These findings strongly suggested that the signal transduction pathway leading to proliferation of synovial cells is transmitted via C-kinase activation. Prostaglandin E2, which is known to stimulate adenylate cyclase, leading to the elevation of intracellular c-AMP level, inhibited the proliferation of synovial cells. This effect could also be mimicked by the addition of a cell permeable c-AMP analog, dibutyryl c-AMP or theophylline. Studies suggest that the feedback signal for proliferation of synovial cells was transmitted through c-AMP. We therefore conclude that signals for stimulation and inhibition of synovial cell proliferation are transmitted through different pathways.

Investigation of guanine-nucleotide-binding protein involvement and regulation of cyclic AMP metabolism in interleukin 1 signal transduction

The involvement of guanine-nucleotide-binding proteins (G-proteins) and regulation of cyclic AMP (cAMP) in interleukin 1 (IL1) signal transduction has been investigated in EL4 and 7OZ/3 cells expressing Type 1 and Type 2 IL1 receptors respectively. Results show that in both cell types IL1 alone failed to induce changes in cellular cAMP levels, and in membrane preparations the cytokine had no significant effect on adenylate cyclase activity. In contrast, forskolin stimulated cAMP levels in cells and membranes. IL1 did not significantly alter GTPase activity or rate of guanosine 5'-[gamma-[35S]thio]triphosphate binding measured in membrane preparations from the EL4 and 7OZ/3 cells. In EL4-cell membrane preparations the kinetics of 125I-IL1 binding were altered in the presence of guanosine 5'-[beta gamma-imido]triphosphate, resulting in the formation of a higher-affinity state for IL1 binding. Adenosine 5'-[beta gamma-imido]triphosphate at the same concentration was without effect. These results suggest that IL1 receptor function may be regulated by guanine nucleotides; however, the mechanism appears to differ from that exhibited by conventional G-protein-linked receptors. The lack of significant effects of IL1 on cAMP metabolism in these cells suggests that alternative pathways must exist to mediate the intracellular responses to stimulation via both types of the IL1 receptor.

Biphasic effect of camp-elevating agents on ICAM-1 expression stimulated by retinoic acid and interferonγ

Incubation of the human glioma cell line HS 683 in the presence of IFN-gamma or retinoic acid strongly stimulates the cell-surface expression of the intercellular adhesion molecule ICAM-1. We have investigated the role of the cAMP-mediated signal transduction pathway in this process and report that pharmacological agents which increased the intracellular levels of cAMP exhibited a biphasic action on ICAM-1 expression in human glioma cell line HS 683. Treatment for 1 hr with 25 microM forskolin or 1 mM isobutylmethylxanthine, or for 12 hr with 100 ng/ml pertussis toxin or 50 micrograms/ml cholera toxin transiently stimulated ICAM-1 expression with a maximal level of expression 8 hr post treatment, after which time ICAM-1 expression returned to the basal level. On the other hand, such pretreatments inhibited the inducing effects of either retinoic acid or IFN-gamma. Indeed, 24 hr after treatment with cAMP-elevating agents, both the retinoic-acid- and the IFN-gamma-induced ICAM-1 expression were inhibited by 60 to 80%, with a maximal 90 to 100% inhibition 72 hr post treatment. This inhibition of the cell-surface expression of ICAM-1 was confirmed at the mRNA level. The intracytoplasmic levels of cAMP were also quantified following treatments with forskolin, retinoic acid or IFN-gamma. In response to forskolin, cAMP levels increased 30-fold within 5 min, whereas a 10-fold increase occurred 60 min following treatment with 10 microM retinoic acid. Interferon gamma, in contrast, did not induce cAMP accumulation. These results were also correlated with an in vitro activation of adenylyl cyclase activity by retinoic acid and inhibition of this activity by IFN-gamma, in a dose-dependent and a GTP-dependent manner. Our results suggest that the suppression of IFN-gamma-induced ICAM-1 expression, obtained upon pre-treatment with cAMP-elevating agents, is due to direct antagonism with IFN-gamma action on adenylyl cyclase. However, the inhibition of retinoic-acid-induced ICAM-1 expression cannot be explained by the same mechanisms. The timing of adenylyl cyclase stimulation and cAMP accumulation, as well as the levels of cAMP accumulation, are probably involved in this inhibition. Our results also emphasize the fact that the induction of ICAM-1 expression is a multi-step process implicating different transductional signals among which cAMP might be involved as a second messenger.

Increased cyclic AMP levels enhance IL-1 alpha and IL-1 beta mRNA expression and protein production in human myelomonocytic cell lines and monocytes

The effects of increasing intracellular cAMP levels on IL-1 alpha and IL-1 beta mRNA expression and IL-1 production in human monocytes and nonlymphoid hematopoietic cell lines were examined. Peripheral monocytes and myelomonocytic cell lines could be stimulated by LPS or phorbol myristate acetate (PMA) to express IL-1 mRNA. Dibutyryl cAMP, 8-bromo-cAMP, forskolin, cholera toxin, PGE1, and PGE2 synergized with PMA or LPS to increase the accumulation in cell lines of IL-1 alpha mRNA by up to 50-fold and that of IL-1 beta mRNA by 10- to 20-fold compared to LPS or PMA alone. This increase in IL-1 alpha and IL-1 beta mRNA accumulation was more modest in monocytes. The synergistic stimulation was due to enhanced IL-1 gene transcription rate rather than increased IL-1 mRNA stability. Despite this marked increase in IL-1 mRNA accumulation, IL-1 protein synthesis in these cells was increased by only twofold. Thus, IL-1 synthesis in monocytes and myelomonocytic cell lines is under stringent translational control.

Studies on the autocrine activation of a synovial cell line

The lapine synovial cell line HIG-82 secretes factors that activate cultures of articular chondrocytes. We showed that these "chondrocyte-activating factors" (CAF) also activate quiescent cultures of HIG-82 cells in an autocrine fashion. After exposure to partially purified preparations of CAF, HIG-82 cells increased their synthesis of prostaglandin E2 (PGE2) and the neutral proteinases collagenase, gelatinase, and stromelysin. CAF also induced their own synthesis. Both PGE2 synthesis and endogenous production of CAF started to increase between 1 and 3 h after treatment of cells with exogenous CAF, but the neutral proteolytic activity of the conditioned medium took approximately 12 h to increase. Induction of neutral proteinases by CAF was inversely related to the degree of cell confluency, whereas their induction by phorbol myristate acetate (PMA) was independent of this parameter. Both CAF and PMA provoked morphologic changes in subconfluent cultures of HIG-82 cells. Although the intracellular concentration of free Ca2+ increased rapidly in response to CAF, the results of experiments with calcium channel blockers and ionophores failed to support a role for Ca2+ fluxes in induction of neutral proteinases. In similar types of experiments, no evidence could be found to implicate fluxes in cyclic AMP or cyclic GMP in the induction of collagenase, gelatinase, or stromelysin. Because PMA is such a strong inducer of these enzymes, protein kinase C may be involved in signal transduction, but further work is needed to determine whether this is so.

Interleukin-1 beta decreases HLA class II expression on a glioblastoma multiforme cell line

Antigens encoded within the major histocompatibility complex (MHC) are not normally expressed in the central nervous system (CNS), but can be induced by treatment with interferon-gamma (IFN-gamma). Other cytokines released during an inflammatory process can potentially influence MHC expression as well. One cytokine of interest is interleukin-1 (IL-1), an immunoregulatory polypeptide that is produced by macrophages and also by cells in the CNS. In this study, the effect of IL-1 beta on MHC expression in a human glioblastoma multiforme cell line, U-105 MG, has been examined. Treatment of U-105 MG with 10 U IL-1 beta/ml for a period of 5 days resulted in a decrease in constitutive cell surface HLA class II expression and limited the induction of class II by IFN-gamma. This effect was also observed on steady-state levels of class II RNA and could be neutralized with antibodies to IL-1 beta. All class II transcripts examined (HLA-DR, -DQ, and -DP alpha and beta) were affected. Class I expression was only marginally changed by IL-1 beta treatment. A minimal concentration of 1 U IL-1 beta/ml was required to reduce class II expression and a kinetics experiment indicated that U-105 MG must be treated for at least 4 days with IL-1 beta for a decrease in class II expression to be observed. This study suggests that IL-1 may play a role in limiting immunoreactivity in the CNS by limiting class II induction.

Interleukin 2 counteracts the inhibition of cytotoxic T lymphocytes by cholera toxin in vitro and in vivo

Cholera toxin irreversibly activates a 43-kDa guanosine triphosphate (GTP)-binding protein by adenosine diphosphate ribosylation, resulting in activation of adenylate cyclase and increased intracellular levels of cyclic adenosine monophosphate (cAMP). Because increases in intracellular cAMP inhibit interleukin 2 (IL 2) expression and cytotoxic T lymphocyte (CTL) generation and function in vitro and in vivo, we hypothesized that IL 2 may counteract the inhibition of CTL by cholera toxin. Activated CTL treated with IL 2 were protected from the inhibitory effects of cholera toxin. IL 2 also counteracted the inhibitory effect of cholera toxin on steady-state levels of CTL-specific serine esterase mRNA. Given the putative role of serine esterase for in vitro generated CTL effector activity, these results may account for recovery of CTL activity. Although IL 2 restored CTL function and serine esterase transcription, it did not block cholera toxin-catalyzed ribosylation of the 43-kDa GTP-binding protein, nor did it prevent the accumulation of intracellular levels of cAMP. In vivo, C57BL/6 mice challenged with the allogeneic tumor P815 had suppressed CTL function when cholera toxin was administered. These cholera toxin-treated mice died of tumor overgrowth, whereas untreated mice rejected the allogeneic tumor. Co-treatment of alloimmunized mice with cholera toxin and IL 2 prevented death from tumor overgrowth and restored CTL function; 67% of these mice survived. These data provide evidence that IL 2 acts in CTL through a mechanism independent of cholera toxin-sensitive GTP-binding protein in vitro and in vivo, despite elevated intracellular cAMP levels.

Evidence that responses of articular chondrocytes to interleukin-1 and basic fibroblast growth factor are not mediated by protein kinase C

After exposure to human recombinant interleukin-1 (hrIL-1), chondrocytes increase their synthesis of prostaglandin E2 (PGE2) and neutral metalloproteinases (NMPs). This response, known as chondrocyte activation, is also elicited by partially purified preparations of rabbit synovial IL-1, known as 'chondrocyte activating factors' (CAF). CAF activates chondrocytes more strongly than does hrIL-1, probably because it contains additional growth factors. Basic fibroblast growth factor (bFGF) is one such factor, although CAF also contains others which modulate the activation of chondrocytes. Chondrocyte activation by hrIL-1 is strongly potentiated by bFGF and phorbol myristate acetate (PMA). A series of experiments was conducted to examine the possible role of protein kinase C (PKC) in mediating these effects. Inhibitors of PKC partially blocked the induction of NMPs by CAF and completely suppressed the potentiating effect of PMA. However, induction by 10 units of hrIL-1/ml and potentiation by bFGF were not affected by these inhibitors. Furthermore, cells whose PKC had been down-regulated by prolonged exposure to PMA remained responsive to IL-1. Surprisingly, inhibitors of PKC greatly increased the amounts of NMPs produced in response to a low dose (1 unit/ml) of hrIL-1. These inhibitors also enhanced the synthesis of PGE2 by cells responding to 1 and 10 units of hrIL-1/ml. Phosphorylation of the 80 kDa substrate for PKC was augmented by PMA and CAF, but not by hrIL-1 or bFGF. Moreover, Western-blotting techniques, which confirmed translocation of PKC in response to PMA and CAF, did not detect translocation in cells treated with hrIL-1 or bFGF. Western blotting also demonstrated the presence of PKC isoenzyme type III (alpha), but not types I (gamma) or II (beta). These data argue that PKC does not mediate the effects of hrIL-1 or bFGF in chondrocytes. However, CAF contains additional substances which activate this enzyme and whose effects may in part be mediated by PKC.

Dominant and recessive mutations define functional domains of Toll, a transmembrane protein required for dorsal-ventral polarity in the Drosophila embryo

The asymmetry of the dorsal-ventral pattern of the Drosophila embryo appears to depend on the ventral activation of the transmembrane Toll protein. The Toll protein is found around the entire dorsal-ventral circumference of the embryo, and it appears to act as a receptor for a ventral, extracellular signal and to then relay that signal to the cytoplasm in ventral regions of the embryo. Three of five recessive loss-of-function alleles of Toll are caused by point mutations in the region of the cytoplasmic domain of Toll that is similar to the mammalian interleukin-1 receptor, supporting the hypothesis that Toll acts as a signal-transducing receptor. Nine dominant gain-of-function alleles that cause Toll to be active in dorsal, as well as ventral, regions of the embryo are caused by mutations in the extracellular domain. Three of the dominant alleles appear to cause the protein to be constitutively active and are caused by cysteine-to-tyrosine changes immediately outside the transmembrane domain. All six of the remaining dominant alleles require the presence of a wild-type transmembrane Toll protein for their ventralizing effect and all encode truncated proteins that lack the transmembrane and cytoplasmic domains.

Simultaneous expression and regulation of G-CSF and IL-6 mRNA in adherent human monocytes and fibroblasts

The regulation of granulocyte-colony stimulating factor (G-CSF) and interleukin-6 (IL-6) mRNA was studied in human adherent monocytes in response to the protein kinase C activator, oleolyl-acetylglycerol (OAG), the calcium-ionophore A23187 and the cyclic AMP elevating agents, dibutyryl c-AMP (DBcAMP), cholera toxin and isobutyl-methylxanthine (IBMX). G-CSF and IL-6 transcripts were simultaneously expressed in response to OAG, A23187, DBcAMP, IBMX and cholera toxin. However, the time course demonstrated a difference; a rapid induction by OAG and A23187 and a delayed pattern by cAMP elevating agents. In addition it appeared that the induction of CSFs by DBcAMP was independent of the adherence procedure or the presence of fetal bovine serum but could be counteracted by the simultaneous addition of H8, an inhibitor of the cAMP dependent kinases. Finally, experiments were performed to study in how far comparable mechanisms operate in other cell types. Human fetal lung fibroblasts were stimulated with A23187, DBcAMP and OAG. All these agents induced simultaneous expression of G-CSF and IL-6 mRNA and secretion of proteins, indicating that different signalling pathways exist in both cell types which regulate the expression of both genes.

Cyclic AMP-independent activation of transcription factor NF-kappa B in HL60 cells by tumor necrosis factors alpha and beta

No correlation exists in HL60 cells between NF-kappa B activation by tumor necrosis factor (TNF alpha) and TNF beta and intracellular levels of cyclic AMP. Cyclic AMP levels did not increase upon treatment of cells with each of these cytokines, although NF-kappa B was activated. Forskolin or 1-isobutyl-3-methylxanthine drastically increased intracellular levels of cyclic AMP, but neither activated NF-kappa B nor influenced TNF-induced NF-kappa B activation.

Cyclic AMP-independent activation of transcription factor NF-kappa B in HL60 cells by tumor necrosis factors alpha and beta

No correlation exists in HL60 cells between NF-kappa B activation by tumor necrosis factor (TNF alpha) and TNF beta and intracellular levels of cyclic AMP. Cyclic AMP levels did not increase upon treatment of cells with each of these cytokines, although NF-kappa B was activated. Forskolin or 1-isobutyl-3-methylxanthine drastically increased intracellular levels of cyclic AMP, but neither activated NF-kappa B nor influenced TNF-induced NF-kappa B activation.

Ca2+ responses to interleukin 1 and tumor necrosis factor in cultured human skin fibroblasts. Possible implications for Reye syndrome

Elevated concentrations of cytokines were found in the plasma of patients acutely ill with Reye syndrome (RS) but not in control subjects or recovered RS patients. To determine whether this disorder involves a genetically determined abnormal response to cytokines, the effects of tumor necrosis factor (TNF) and IL-1 on intracellular free Ca2+ were compared in cultured skin fibroblasts from control subjects and patients with RS. IL-1 and TNF caused rapid, transient, and concentration-dependent increases in cytosolic free Ca2+. The peak cytosolic free Ca2+ was greater and occurred at higher concentrations of IL-1 and TNF in patient cells than in cells from age-matched controls. In control cells, the Ca2+ transient diminished sharply with increasing amounts of IL-1 or TNF above the maximum stimulatory concentration. In contrast, in patient fibroblast this bell-shaped curve of concentration dependency was much less apparent. Bradykinin-stimulated Ca2+ transients were similar in the two groups and did not exhibit the bell-shaped concentration dependency. Thus, plasma cytokine levels are elevated in RS patients and the Ca2+ response to cytokines is increased in cells derived from these patients. We propose that the increased response reflects a genetic defect in cytokine receptor-modulated signal transduction.

Interleukin-1 synergy with phosphoinositide pathway agonists for induction of interleukin-2 gene expression: molecular basis of costimulation

The macrophage-derived cytokine interleukin-1 (IL-1) can provide a second signal with antigen to elicit production of interleukin-2 (IL-2) by helper T cells. The pathway(s) involved remains controversial, with protein kinase C and cyclic AMP (cAMP) invoked as possible second messengers. In the murine thymoma EL4.E1, IL-1 could synergize with the phosphoinositide pathway, because the cells made higher levels of IL-2 in the presence of IL-1 than could be induced by phorbol ester plus calcium ionophore alone. IL-1 is unlikely to act through a sustained increase in cAMP in these cells because it did not raise cAMP levels detectably and because IL-1 and forskolin had opposite effects on IL-2 gene expression. Inducible expression of a transfected reporter gene linked to a cloned fragment of the murine IL-2 gene promoter was initially increased by IL-1 costimulation, implying that IL-1 can increase the rate of transcription of IL-2. The minimal promoter elements required for iL-1 responsiveness were located within 321 bp of the IL-2 RNA cap site, and further upstream sequences to -2800 did not modify this response. IL-1 costimulation resulted in enhanced activity of both an inducible NF-kappa B-like factor and one of two distinct AP-1-like factors that bind to IL-2 regulatory sequences. Neither was induced, however, by IL-1 alone. Another AP-1-like factor and NFAT-1, while inducible in other cell types, were expressed constitutively in the EL4.E1 cells and were unaffected by IL-1. These results are discussed in terms of the combinatorial logic of IL-2 gene expression.

Cyclic AMP mimics, but does not mediate, interleukin-1- and tumour-necrosis-factor-stimulated phospholipase A2 secretion from rat renal mesangial cells

We have previously shown that recombinant interleukin 1 (IL-1) and recombinant tumour necrosis factor (TNF) synergistically stimulate phospholipase A2 release from mesangial cells. We now report that treatment of mesangial cells with the beta-agonist salbutamol, prostaglandin E2 (PGE2), cholera toxin or forskolin, which all activate adenylate cyclase, increased release of phospholipase A2 activity. Likewise, addition of a membrane-permeant cyclic AMP (cAMP) analogue or the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine enhanced release of phospholipase A2 activity from mesangial cells. There was a lag period of about 8 h before a significantly enhanced secretion could be detected. Furthermore, actinomycin D or cycloheximide completely suppressed cAMP-stimulated secretion of phospholipase A2. Angiotensin II, the phorbol ester phorbol 12-myristate 13-acetate, the Ca2+ ionophore A23187 and a membrane-permeant cGMP analogue did not stimulate phospholipase A2 release from the cells. Treatment with indomethacin completely inhibited IL-1 beta- and TNF-stimulated PGE2 synthesis, without having any effect on phospholipase A2 secretion, thus excluding cytokine-induced PGE2 synthesis as the mediator of phospholipase A2 release. Neither IL-1 beta nor TNF induced any increase in intracellular cAMP in mesangial cells. Furthermore, incubation of the cells with 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, did not block cytokine-stimulated phospholipase A2 secretion. In addition, IL-1 beta and TNF synergistically interacted with forskolin to stimulate phospholipase A2 release from the cells. The protein kinase inhibitors H-8, staurosporine, K252a and amiloride inhibited IL-1 beta- and TNF-stimulated phospholipase A2 secretion. However, high concentrations that inhibit other protein kinases were needed. These observations suggest that IL-1 beta and TNF cause secretion of phospholipase A2 by a mechanism independent of cAMP. The signalling pathways used by IL-1 beta and TNF may involve a protein kinase that is probably different from protein kinase A or protein kinase C.

Distinct regulation of the interleukin-1 and interleukin-6 response elements of the rat haptoglobin gene in rat and human hepatoma cells

The transcription rate of the haptoglobin (Hp) gene is stimulated by interleukin-1 (IL-1), IL-6, and dexamethasone in rat hepatoma (H-35) cells. To identify the cis-acting regulatory elements responsive to these hormones, various lengths of 5' Hp gene-flanking regions, including the promoter, were inserted into chloramphenicol acetyltransferase gene expression vectors and transiently introduced into H-35 cells. The first 4 kb of 5' region mediated a severalfold increase in expression after treatment with IL-6 and dexamethasone. No response to IL-1 was detectable. When, however, upstream sequences were deleted to position -165 relative to the transcription start site, a significant stimulation by IL-1 was gained without appreciably affecting the IL-6 response. With the apparent removal of an inhibitory sequence, the promoter-proximal 165-bp region also displayed a severalfold enhanced response to the combination of dexamethasone, IL-1, and IL-6. The sequence from -165 to -147, termed the A-element, was found to be crucial for all hormone regulatory functions. Two copies of the A-element linked to a heterologous promoter responded to the three hormones, but to a lesser degree than in the Hp gene promoter context. The regulatory elements of the rat Hp gene were similarly active in human hepatoma cells. Optimal regulation by IL-6 in HepG2 cells was, however, independent of the A-element. The A-element functioned in these cells exclusively as an IL-1 response sequence. The results suggest that genomic sequences upstream of the rat Hp gene suppress the regulation by specific cytokines more prominently in transient expression assays than in the normal chromosomal context. Moreover, the functional comparison indicated that specific regulatory regions of the rat Hp gene do not function identically in different hepatic cell types.

Interleukin-1 synergy with phosphoinositide pathway agonists for induction of interleukin-2 gene expression: molecular basis of costimulation

The macrophage-derived cytokine interleukin-1 (IL-1) can provide a second signal with antigen to elicit production of interleukin-2 (IL-2) by helper T cells. The pathway(s) involved remains controversial, with protein kinase C and cyclic AMP (cAMP) invoked as possible second messengers. In the murine thymoma EL4.E1, IL-1 could synergize with the phosphoinositide pathway, because the cells made higher levels of IL-2 in the presence of IL-1 than could be induced by phorbol ester plus calcium ionophore alone. IL-1 is unlikely to act through a sustained increase in cAMP in these cells because it did not raise cAMP levels detectably and because IL-1 and forskolin had opposite effects on IL-2 gene expression. Inducible expression of a transfected reporter gene linked to a cloned fragment of the murine IL-2 gene promoter was initially increased by IL-1 costimulation, implying that IL-1 can increase the rate of transcription of IL-2. The minimal promoter elements required for iL-1 responsiveness were located within 321 bp of the IL-2 RNA cap site, and further upstream sequences to -2800 did not modify this response. IL-1 costimulation resulted in enhanced activity of both an inducible NF-kappa B-like factor and one of two distinct AP-1-like factors that bind to IL-2 regulatory sequences. Neither was induced, however, by IL-1 alone. Another AP-1-like factor and NFAT-1, while inducible in other cell types, were expressed constitutively in the EL4.E1 cells and were unaffected by IL-1. These results are discussed in terms of the combinatorial logic of IL-2 gene expression.

Establishment of a cyclic adenosine monophosphate-dependent growing human T-cell line derived from an interleukin-2-dependent cell line

An adenosine 3',5'-cyclic monophosphate (cAMP)-dependent growing cell line called CT-Mat was established by the long-term cultivation of an interleukin-2 (IL-2)-dependent human T-cell line, ILT-Mat, in the presence of cholera toxin instead of IL-2. CT-Mat cells can grow in the medium containing either cholera toxin or forskolin or cAMP derivatives. Although the CT-Mat cell line can still grow dependent on IL-2, the forskolin-induced growth of CT-Mat cells was demonstrated not to be mediated by an autocrine mechanism of IL-2 or any other growth factor. The intracellular cAMP level was elevated by treatment with the chemical agents but little by treatment with IL-2. These suggest that cAMP transduces intracellular growth signals different from those through the IL-2 receptor in an IL-2-dependent T-cell line CT-Mat.

Distinct regulation of the interleukin-1 and interleukin-6 response elements of the rat haptoglobin gene in rat and human hepatoma cells

The transcription rate of the haptoglobin (Hp) gene is stimulated by interleukin-1 (IL-1), IL-6, and dexamethasone in rat hepatoma (H-35) cells. To identify the cis-acting regulatory elements responsive to these hormones, various lengths of 5' Hp gene-flanking regions, including the promoter, were inserted into chloramphenicol acetyltransferase gene expression vectors and transiently introduced into H-35 cells. The first 4 kb of 5' region mediated a severalfold increase in expression after treatment with IL-6 and dexamethasone. No response to IL-1 was detectable. When, however, upstream sequences were deleted to position -165 relative to the transcription start site, a significant stimulation by IL-1 was gained without appreciably affecting the IL-6 response. With the apparent removal of an inhibitory sequence, the promoter-proximal 165-bp region also displayed a severalfold enhanced response to the combination of dexamethasone, IL-1, and IL-6. The sequence from -165 to -147, termed the A-element, was found to be crucial for all hormone regulatory functions. Two copies of the A-element linked to a heterologous promoter responded to the three hormones, but to a lesser degree than in the Hp gene promoter context. The regulatory elements of the rat Hp gene were similarly active in human hepatoma cells. Optimal regulation by IL-6 in HepG2 cells was, however, independent of the A-element. The A-element functioned in these cells exclusively as an IL-1 response sequence. The results suggest that genomic sequences upstream of the rat Hp gene suppress the regulation by specific cytokines more prominently in transient expression assays than in the normal chromosomal context. Moreover, the functional comparison indicated that specific regulatory regions of the rat Hp gene do not function identically in different hepatic cell types.

The cytokine response element of the rat alpha 1-acid glycoprotein gene is a complex of several interacting regulatory sequences

Expression of the rat alpha 1-acid glycoprotein gene is stimulated by interleukin-1 (IL-1) and interleukin-6 (IL-6) and is synergistically enhanced by the combination of the two. The distal regulatory element (DRE), a 142-base-pair (bp) sequence located 5 kilobase pairs upstream of the transcriptional start site, appears to be crucial for this cytokine response. The cytokine-specific regulatory sequences within the DRE have been identified by inserting individual DRE subregions, selected combinations of these, or a few linker mutated fragments into a plasmid containing an enhancerless simian virus 40 promoter linked to the chloramphenicol acetyltransferase gene. The regulatory activity was determined in transiently transfected human and rat hepatoma cells. The IL-1 response region was confined to the 5'-most 62 bp of the DRE, and its function seemed to depend on at least two separate components. The same region was also responsive to phorbol ester treatment. The IL-6 regulatory function was dependent on a 54-bp sequence located within the 3' half of the DRE. When the IL-1 response region was recombined with the IL-6 regulatory region of the DRE or with IL-6 response elements of other plasma protein genes, a strong cooperative action by IL-1 and IL-6 was achieved. The functional DRE sequences were recognized by nuclear proteins extracted from rat liver and hepatoma cells. However, no cytokine-inducible binding activity was detectable, which suggests that transcriptional regulation through the DRE might be controlled by posttranslational modification of constitutively bound trans-acting factors.

The cytokine response element of the rat alpha 1-acid glycoprotein gene is a complex of several interacting regulatory sequences

Expression of the rat alpha 1-acid glycoprotein gene is stimulated by interleukin-1 (IL-1) and interleukin-6 (IL-6) and is synergistically enhanced by the combination of the two. The distal regulatory element (DRE), a 142-base-pair (bp) sequence located 5 kilobase pairs upstream of the transcriptional start site, appears to be crucial for this cytokine response. The cytokine-specific regulatory sequences within the DRE have been identified by inserting individual DRE subregions, selected combinations of these, or a few linker mutated fragments into a plasmid containing an enhancerless simian virus 40 promoter linked to the chloramphenicol acetyltransferase gene. The regulatory activity was determined in transiently transfected human and rat hepatoma cells. The IL-1 response region was confined to the 5'-most 62 bp of the DRE, and its function seemed to depend on at least two separate components. The same region was also responsive to phorbol ester treatment. The IL-6 regulatory function was dependent on a 54-bp sequence located within the 3' half of the DRE. When the IL-1 response region was recombined with the IL-6 regulatory region of the DRE or with IL-6 response elements of other plasma protein genes, a strong cooperative action by IL-1 and IL-6 was achieved. The functional DRE sequences were recognized by nuclear proteins extracted from rat liver and hepatoma cells. However, no cytokine-inducible binding activity was detectable, which suggests that transcriptional regulation through the DRE might be controlled by posttranslational modification of constitutively bound trans-acting factors.