Differential induction and decay of manganese superoxide dismutase mRNAs.

Human manganese superoxide dismutase (MnSOD) is encoded by two mRNAs of 4 and 1 kb, respectively. These mRNAs are transcribed from the same gene and have an identical coding sequence, but differ in the 3' untranslated sequence because of alternate polyadenylation. Tumor necrosis factor-alpha (TNF) induced both 4- and 1-kb mRNAs in all the human cell lines examined. However, the relative expression of these mRNAs varied significantly among different cell lines after an 8-h treatment with TNF. Therefore, the time course of induction by TNF and the decay of MnSOD mRNAs after TNF removal were analyzed. The rate of accumulation of the 4-kb mRNA was initially much greater than that of the 1-kb mRNA, suggesting that the 4-kb mRNA was produced faster than the 1-kb mRNA. The rapid accumulation of the 4-kb mRNA was offset after a few hours by an enhanced rate of decay. The half-life of the 4-kb mRNA was approximately 2-4 h in different cells while that of the 1-kb mRNA was approximately 10-12 h. This different half-life of mRNAs that encode the same protein suggests that their relative expression is also regulated by a post-transcriptional mechanism affecting their turnover. Additional evidence supporting the differential decay of the two MnSOD mRNAs was obtained by incubation in a rabbit reticulocyte cell-free system; the 4-kb mRNA decayed rapidly while the 1-kb mRNA appeared to be stable.

Tumor necrosis factor increases stability of interleukin-1 mRNA by activating protein kinase C.

The mRNAs coding for interleukin-1 alpha (IL-1 alpha) and IL-1 beta are constitutively transcribed but do not accumulate in human diploid fibroblasts and in fibrosarcoma cells. Treatment of these cells with tumor necrosis factor (TNF) induces accumulation of IL-1 mRNA by an unknown mechanism. This induction of IL-1 mRNA was investigated in HT-1080 cells. The induction was quite fast, with maximum levels of IL-1 alpha and beta mRNA reached 4 h after addition of TNF. Nuclear run-off experiment showed that TNF did not increase the rate of transcription of IL-1 mRNA. This mRNA was apparently unstable in untreated cells, but it accumulated in cycloheximide-treated cells. Phorbol esters induced IL-1 mRNA, suggesting that activation of protein kinase C was responsible for the accumulation of this mRNA. This hypothesis was confirmed by experiments with the PKC inhibitors staurosporine and calphostin C, which prevented the induction of IL-1 mRNA by TNF and accelerated the decay of this mRNA in cells pretreated with TNF. Both IL-1 alpha and IL-1 beta were detected in TNF-treated cells by Western blot analysis and enzyme-linked immunosorbent assay. These results indicate that the TNF-mediated induction of IL-1 can be entirely accounted for by stabilization of this mRNA.

Expression of messenger RNAs for complement inhibitors in human tissues and tumors.

The mRNAs coding for three complement inhibitors produced by human cells, complement cytolysis inhibitor (CLI), decay-accelerating factor (DAF), and CD59, are characteristically distributed among normal tissues. High levels of CLI mRNA are expressed in tissues that express low levels of DAF mRNA and vice versa. Therefore, the expression of these mRNAs shows a mutually exclusive relationship, with the possible exception of the lung, where all these mRNAs are expressed. In contrast, CD59 mRNA is rather uniformly expressed in all tumor cell lines examined, whereas the mRNA for either of the two other complement inhibitors is overexpressed in some specific tumor cells, e.g., HeLa cells overexpress DAF mRNA, while A172 cells overexpress CLI mRNA. These two cell lines were resistant to antibody-dependent complement cytotoxicity. Expression of CLI and DAF mRNA was induced in cells treated with the antitumor drug N-(chloroetyl)-N'-cyclohexyl-N-nitrosourea; these cells became resistant to complement cytotoxicity. A similar pattern of expression was detected in tumor samples obtained during surgery, with a relatively uniform expression of CD59 mRNA and occasional overexpression of CLI or DAF mRNA. These findings suggest that overexpression of complement inhibitors mRNA and of the corresponding proteins may contribute to tumor cell resistance to complement-mediated cytotoxicity.

Expression of interleukin 1-inducible genes and production of interleukin 1 by aging human fibroblasts.

The interleukin 1 (IL-1)-inducible mRNAs for plasminogen activator inhibitor type 2, manganese superoxide dismutase, and urokinase are overexpressed in old (greater than 70% of life-span completed) but not in young (less than 40% of life-span completed) human foreskin fibroblasts. Furthermore, the activity of this superoxide dismutase is greater in old than in young fibroblasts. IL-1 beta mRNA is detected by Northern blot analysis in old fibroblasts and its expression is further enhanced by a treatment with IL-1 alpha. IL-1 alpha and IL-1 beta mRNAs are detected in old foreskin and lung fibroblasts by a sensitive reverse transcription-PCR assay. IL-1 mRNA is consistently expressed after fibroblasts have completed 85% of their in vitro life-span; an assay with specific antibodies shows that IL-1 alpha is present in these fibroblasts. Prolonged treatment with IL-1 receptor antagonist decreases the levels of IL-1 alpha and of IL-1 alpha and IL-1 beta mRNAs. This observation suggests that IL-1 receptor antagonist inhibits an autocrine loop responsible for IL-1 expression. IL-1 mRNA accumulates in young fibroblasts treated with cycloheximide, suggesting that it is transcribed but unstable in these cells; accumulation of IL-1 mRNA in old fibroblasts may be due at least in part to increased stability. IL-1 alpha stimulates DNA synthesis in young fibroblasts but has progressively less effect as the cells age in culture. These data indicate that IL-1 is "constitutively" produced by aging fibroblasts and that IL-1 induces the expression of specific proteins in these cells. The mechanism for this constitutive production of IL-1 is explored in this paper.

Expression of porcine complement cytolysis inhibitor mRNA in cultured aortic smooth muscle cells. Changes during differentiation in vitro.

Porcine smooth muscle cells (SMC) grown to a high density monolayer culture undergo a morphological transition in which the cells draw away from the substrate and form multicellular nodules. The cells within the nodule resemble SMC in the aortic media and in some atherosclerotic plaques. The process of nodule formation is associated with the enhanced production of a secreted 38-kDa glycoprotein. To characterize the 38-kDa protein and its expression, a cDNA clone (pc38K) was isolated by immunological screening of an expression library. The 1646-base pair cDNA contains a single open reading frame encoding 446 amino acids. This sequence shows 72% homology with the human complement cytolysis inhibitor (CLI), also called serum protein-40,40, and 68% identity with rat sulfated glycoprotein-2. Based on this homology, we refer to the protein encoded by pc38K as CLI. This polypeptide includes a potential signal sequence, seven glycosylation sites and 10 cysteines in two clusters of five each. Southern blot analysis reveals that a single copy gene encoding CLI is present in mammals and chicken. In Northern blot analysis of SMC RNA, pc38K hybridizes to a mRNA of about 1.9 kilobases that is preferentially expressed in nodular SMC. The steady state level of this mRNA increases as the cultures begin to form multilayered regions. High levels of the mRNA persist after the cells are trypsin-dissociated. Culture medium conditioned by nodular SMC also induces an increase of CLI mRNA. Analysis of RNA extracted from porcine tissues show the highest levels of CLI mRNA in brain and liver; lower levels are detected in other tissues, including the aorta. Possible functions for the CLI are discussed.

Reduced expression of manganese superoxide dismutase in cells resistant to cytolysis by tumor necrosis factor.

Tumor necrosis factor (TNF) induces synthesis of manganese superoxide dismutase (MnSOD). It was previously shown that overexpression of MnSOD protected some mammalian cells from TNF cytotoxicity. The purpose of this study was to establish whether MnSOD was increased in cells selected for resistance to cytolysis by TNF in combination with cycloheximide. Melanoma SK-MEL-109 and HeLa cell-resistant variants were selected by repeated treatments with TNF and cycloheximide. The SK-MEL-109 variants had relatively low levels of MnSOD that were inducible by TNF. Surprisingly, the HeLa variants had very low levels of MnSOD that were poorly inducible by either TNF or interleukin-1 alpha. Therefore, an elevated level of MnSOD was not required to protect these cells from TNF-mediated cytolysis. The HeLa variants were more sensitive than parental cells to superoxide radical (O2-) generating compounds, such as paraquat or xanthine/xanthine oxidase. Pretreatment of these variants with TNF did not provide protection against damage by superoxide radicals.

Protection from tumor necrosis factor-mediated cytolysis by overexpression of plasminogen activator inhibitor type-2.

Pretreatment of HT-1080 fibrosarcoma cells with tumor necrosis factor (TNF) induced resistance to the cytolytic activity of this cytokine in combination with cycloheximide. This resistance correlated with the synthesis of plasminogen activator inhibitor type-2 (PAI-2). HT-1080 cells were transfected with a PAI-2 expression vector in both sense and antisense orientation. The resistance to TNF-mediated cytolysis of transfected cell clones was correlated with the level of PAI-2 expression. Cells expressing antisense PAI-2 RNA showed reduced expression of PAI-2 and increased sensitivity to TNF-mediated cytolysis. Cells expressing constitutively PAI-2 were treated with TNF and cycloheximide to select cells with increased resistance to cytolysis and enhanced PAI-2 expression. PAI-2 gradually disappeared during a treatment with TNF and cycloheximide. This finding suggested that PAI-2 formed a complex with a target proteinase, which could be involved in mediating the cytolytic activity of TNF.

Modulation of neurite outgrowth in neuroblastoma cells by protein kinase C and platelet-activating factor.

Previous reports have shown that thrombin and activators of protein kinase C (PKC) inhibit neurite outgrowth (NOG) in neuroblastoma cells cultured in serum-free medium. Therefore, we tested the hypothesis that PKC activation mediates the effect of thrombin on NOG in murine neuroblastoma NB-2a cells. After 2 h in serum-free medium, 70% of the cells displayed neurites; addition of 300 ng/ml thrombin reduced NOG to 24% within 1 h. This inhibition was reduced after NB-2a cells were pretreated for 24 h with 200 nM phorbol dibutyrate down-regulate PKC. Thrombin and phorbol 12-myristate 13-acetate inhibited NOG in an additive way and the protein kinase inhibitors H-7, H-8, and HA1004 reversed the effect of thrombin on NOG with a rank order of activity consistent with PKC inhibition. Furthermore, PKC was translocated from the cytosol to a membrane-bound form 5 to 10 min after addition of thrombin. These findings indicate that thrombin inhibits NOG through a PKC-dependent pathway. Thrombin stimulates the synthesis of the phospholipid platelet-activating factor (PAF) in some cells. However, NOG was markedly stimulated when PAF or its analogue carbamyl-PAF were added to NB-2a cells in medium with serum. Furthermore, the PAF receptor antagonist SRI 63072 inhibited NOG in NB-2a cells in serum-free medium. These cells accumulated PAF with kinetics similar to that of NOG inducPAF was synthesized by the de novo pathway, as shown by the incorporation of [3H]choline. These findings suggest that PAF is a mediator of NOG in NB-2a cells. Thrombin neither stimulates nor inhibits PAF synthesis in these cells.

Inhibition of the synthesis of platelet-activating factor by anti-inflammatory peptides (antiflammins) without methionine.

Antiflammins are synthetic peptides corresponding to a region of similarity between uteroglobin and lipocortin I. These peptides inhibit synthesis of platelet-activating factor and release of arachidonic acid from neutrophils and macrophages stimulated by phagocytosis or tumor necrosis factor. Antiflammins containing methionine are inactivated readily in the absence of reducing agents. Novel antiflammins containing alanine or norleucine in place of methionine are inhibitory without added reducing agents, but only when stock solutions are heated to 45 degrees C. Heating may favor hydrophobic interactions between peptide molecules, thereby activating the antiflammins. These peptides are less inhibitory when added after cell stimulation, suggesting that they interfere with the activation of phospholipase A2.

Posttranscriptional regulation of interferon mRNA levels in peritoneal macrophages.

Low levels of beta interferon (IFN) mRNA are transcribed in freshly explanted murine peritoneal macrophages. Nuclear runoff transcription assays show that this "constitutive" IFN-beta-mRNA transcription does not increase in macrophages treated either with lipopolysaccharide or with IFN-gamma, which induce a marked accumulation of this mRNA and greatly increase IFN secretion. Therefore, these agents promote accumulation of IFN-beta mRNA by posttranscriptional mechanisms. The IFN-alpha 2 gene is also constitutively transcribed by macrophages, but the corresponding mRNA does not accumulate in lipopolysaccharide-treated cells.

Tumor necrosis factor alters cytoskeletal organization and barrier function of endothelial cells.

Treatment of human umbilical cord vein endothelial cells with tumor necrosis factor results in marked changes in cell shape and cytoskeletal organization. After 4 h of treatment, these cells loose reciprocal contacts with the formation of intercellular gaps. This retraction reaches a maximum after 6 h when most stress fibers staining for F-actin disappear and vinculin becomes diffused in the cytoplasm. Such changes spontaneously reverse after 24 h in the presence of tumor necrosis factor or after 2 h of incubation in fresh medium. After treatment with tumor necrosis factor, endothelial monolayers become permeable to albumin because of gaps that form between cells. Normal human serum, plasma alpha 1-proteinase inhibitor and an anti-inflammatory peptide that decrease synthesis of platelet-activating factor inhibit the changes induced by tumor necrosis factor. Furthermore, receptor antagonists of platelet-activating factor have the same effect. These findings suggest that platelet-activating factor is a secondary mediator responsible for the changes in cell shape and cytoskeletal organization, and for the leakiness of endothelial monolayers.

Tumor necrosis factor induces contraction of mesangial cells and alters their cytoskeletons.

Cultures of human mesangial cells (MC) were established from the renal cortex of surgical specimen. The characteristic spindle-shaped or stellate appearance of MC was altered after treatment with tumor necrosis factor (TNF). After two hours, the MC retracted and lost reciprocal contacts. Furthermore, this treatment altered the cytoskeletal organization of MC, since a peripheral band of actin and stress fibers disappeared while the streaks of vinculin at focal contacts decreased. These changes were reversible when the MC were cultured in fresh medium. After five minutes of treatment with platelet activating factor (PAF), changes similar to those induced by TNF were observed. Inhibitors of PAF synthesis, such as plasma alpha 1-proteinase inhibitor and an anti-inflammatory peptide, blocked changes induced by TNF, PAF receptor antagonists inhibited changes induced by PAF and also by TNF. These results and the finding that MC are stimulated to produce PAF by TNF suggest that PAF is a secondary mediator of the changes in cell shape and cytoskeletal organization induced by this cytokine.

Effects of different biological response modifiers on interferon expression in bacterial lipopolysaccharide (LPS)-responsive and LPS-hyporesponsive mouse peritoneal macrophages.

We have previously shown that the antiviral state of explanted mouse peritoneal macrophages (PM) decays during in vitro culture and that this decay is much more rapid in Lpsd PM than it is in Lpsn PM. Moreover, Lpsn PM can transfer the antiviral state to other cells, whereas Lpsd PM cannot. In vitro treatment of Lpsn PM with different agents [i.e., bacterial lipopolysaccharide (LPS), interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, macrophage colony-stimulating factor (M-CSF) and antibody to Mac-1 antigen] induced an antiviral state to vesicular stomatitis virus (VSV) which was inhibited by antibodies to IFN-beta. Treatment of Lpsn PM with LPS or IFN-gamma resulted in greater accumulation of IFN-beta mRNA, whereas no change in the barely detectable levels of IFN-alpha mRNA was observed. Marked accumulation of IFN-beta mRNA was also observed in PM after TNF-alpha treatment. M-CSF and IFN-gamma (but not LPS) also induced an IFN-mediated antiviral state in Lpsd PM. Low levels of spontaneous transcription of IFN-beta mRNA were detected in nuclei from Lpsd PM. Treatment of Lpsd PM with IFN-gamma for 3 h resulted in the accumulation of IFN-beta mRNA without any concomitant increase in the transcription of the IFN-beta gene, as determined by run-on transcription assays with isolated nuclei. The addition of as little as I international unit/ml of IFN-gamma to PM resulted in a 100-fold inhibition of VSV yield. As antibodies to IFN-alpha/beta inhibited only a portion of the IFN-gamma-induced antiviral state, such an antiviral state might reflect the synergism between IFN-gamma and endogenous IFN-beta. In fact, the addition of low doses of both IFN-gamma and IFN-beta to either Lpsn or Lpsd PM resulted in synergistic antiviral effects. In vivo treatment of Lpsd mice with granulocyte-macrophage (GM)-CSF, M-CSF, IFN-gamma or Newcastle disease virus rendered peritoneal cells capable of transferring an antiviral state. These results indicate that (i) various stimuli can induce IFN-beta production by PM, (ii) Lpsd PM spontaneously transcribe low levels of IFN-beta mRNA, even though they cannot transfer an antiviral state, (iii) different stimuli, but not LPS, induce a normal IFN response in Lpsd PM, (iv) IFN-gamma increases the accumulation of IFN-beta mRNA in Lpsd PM by post-transcriptional mechanisms and (v) IFN-gamma may act synergistically with endogenous IFN-beta in inducing a potent antiviral state to VSV in PM.

Plasminogen activator inhibitor type-2 is a major protein induced in human fibroblasts and SK-MEL-109 melanoma cells by tumor necrosis factor.

Tumor necrosis factor (TNF) induces the synthesis of two proteins of Mr 42 and 36 kDa in human fibroblasts and SK-MEL-109 melanoma cells. To identify these proteins, a lambda gt10 cDNA library was prepared from the mRNA of TNF-treated SK-MEL-109 cells. By screening this library, we found a cDNA that preferentially hybridized to TNF-induced RNA. Hybrid-selected mRNA was translated into a protein of 42 kDa; cDNA sequence analysis followed by a comparison with other known protein sequences identified this protein with plasminogen activator inhibitor, type-2 (PAI-2). After removal of TNF, PAI-2 mRNA turned over rapidly, with an apparent half-life of approximately 2.5 h. Addition of dexamethasone increased the turnover of this mRNA, suggesting that the level of PAI-2 mRNA could be regulated post-transcriptionally by glucocorticoids. PAI-2 was not secreted, but accumulated in fibroblasts continuously treated with TNF.

Tumour necrosis factor in serum and synovial fluid of patients with active and severe rheumatoid arthritis.

Fifteen serum samples and 29 synovial fluids of patients with rheumatoid arthritis (RA) were examined for the presence of tumour necrosis factor (TNF). The assay for TNF was based on the cytotoxic activity of this cytokine for human melanoma cells in tissue culture. High concentrations of TNF were found in serum samples of patients with severe RA, who had increased erythrocyte sedimentation rate and serum alpha 2 macroglobulin, but decreased haemoglobin and serum iron concentrations. Tumour necrosis factor was also found in the synovial fluid of 16 out of 29 patients. High TNF concentrations were found in fluids with greater than 10(10) leucocytes/l. Tumour necrosis factor was not detected in the serum of normal subjects or in synovial fluid of patients with osteoarthritis. A mediator of inflammation, such as TNF, may contribute to the severity of RA.

Positive and negative regulation of a tumor necrosis factor response in melanoma cells.

Tumor necrosis factor (TNF) elicits a wide variety of responses in target cells by binding to cell surface receptors, but the signal transduced from these receptors in unclear. We examined the role of two different second messenger systems in the regulation of plasminogen activator inhibitor, type 2 (PAI-2) induction by TNF in SK-MEL-109 melanoma cells. Synthesis of PAI-2 and transcription of its mRNA could be induced by a protein kinase C (PKC) activator, phorbol myristate acetate. In addition, induction of PAI-2 synthesis by TNF was blocked by two PKC inhibitors, staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride. The inhibitor of cyclic nucleotide-dependent protein kinases, N-[2-(methylamino)-ethyl]-5-isoquinoline sulfonamide dihydrochloride, was much less effective in decreasing PAI-2 synthesis. Staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride also inhibited both TNF- and phorbol myristate acetate-induced PAI-2 mRNA accumulation. We measured the binding of 3H-labeled phorbol dibutyrate to membrane and cytosol fractions of TNF-treated SK-MEL-109 cells and found a transient redistribution of 3H-labeled phorbol dibutyrate binding from cytosol to membrane fractions in response to TNF. In contrast to the positive regulation by PKC in promoting TNF-induced PAI-2 synthesis cAMP inhibited this response. Pretreatment of cells with agents that raise intracellular cAMP levels completely abolished TNF-induced PAI-2 synthesis. Addition of cAMP-elevating agents during TNF induction could also block PAI-2 synthesis. PAI-2 mRNA accumulation in response to TNF was inhibited, but not completely abolished, by cAMP-elevating agents, suggesting that cAMP also exerted its inhibitory effect at the translation level. The positive regulation of a TNF response by PKC and its negative modulation by cAMP may provide a means for intracellular coordination of signals from interacting extracellular factors in regulating TNF responses in different target cells.

Antiinflammatory peptides (antiflammins) inhibit synthesis of platelet-activating factor, neutrophil aggregation and chemotaxis, and intradermal inflammatory reactions.

Synthetic peptides corresponding to the region of highest similarity between human lipocortin I and rabbit uteroglobin inhibit phospholipase A2 and show potent antiinflammatory activity on the carrageenan-induced rat footpad edema. The peptide HDMNKVLDL (antiflammin-2) inhibits the synthesis of platelet-activating factor (PAF) induced by TNF or phagocytosis in rat macrophages and human neutrophils, and by thrombin in vascular endothelial cells. The peptide MQMKKVLDS (antiflammin-1) is less inhibitory than antiflammin-2 for macrophages and not inhibitory for neutrophils after a 5-min preincubation. This finding suggests that antiflammin-1 is inactivated by neutrophils secretory products, possibly oxidizing agents. Synthesis of PAF is inhibited by antiflammin-2 without an appreciable lag, but this inhibition is reversed when neutrophils or macrophages are washed and incubated in fresh medium. Therefore, antiflammins must be continuously present to inhibit PAF synthesis. Antiflammins block activation of the acetyltransferase required for PAF synthesis, suggesting that this enzyme is another target for the inhibitory activity of antiflammins. These peptides inhibit neutrophil aggregation and chemotaxis induced by complement component C5a. Antiflammin-2 suppresses the increase in vascular permeability and the leukocyte infiltration induced in rats by an Arthus reaction or by intradermal injection of rTNF and C5a.

Selected cytokines promote the synthesis of platelet-activating factor in vascular endothelial cells: comparison between tumor necrosis factor alpha and beta and interleukin-1.

Tumor necrosis factor (TNF alpha and TNF beta) and interleukin-1 (IL-1) are mediators of immunity and inflammation that induce different, but partially overlapping responses in human endothelial cells (HEC). We compared the effect of purified recombinant human TNF alpha, TNF beta and IL-1 on the production of platelet-activating factor (PAF) in HEC. After 30-60 min of treatment with TNF alpha or TNF beta, HEC produce and partially release considerable amounts of PAF, which reach a maximum after 4-6 h. In HEC treated with IL-1 PAF production is detectable after 2 h and peaks at 8-12 h. More than twice as much PAF is produced in response to optimal concentrations of TNF alpha than in response to TNF beta or IL-1. However, PAF synthesis is stimulated by lower molar concentrations of IL-1 than TNF alpha and TNF beta. The ability to induce PAF synthesis in HEC seems to be restricted to these three cytokines, as shown by negative results obtained with other cytokines that activate HEC (interferons, granulocyte- and granulocyte-macrophage colony-stimulating factor, epithelial growth factor, fibroblast growth factor, transforming growth factor beta), or participate in the inflammatory process (IL-6, platelet-derived growth factor).