The Influence of Human Blood Cells on the Solubility of Clot in Urea Solution and Clot Lysis

A proteolytic factor digesting fibrin in concentrate urea solution was demonstrated in granulocytes, erythrocytes and blood platelets.

The proteolytic factor is not dialysable, is inactivated at temp. 80°, and produces low molecular weight peptides when digesting clot. Its action on fibrin is dependent on the presence of urea, but urea does not activate it permanently. In granulocytes the factor is present in an active form, and in red blood cells it is located in the stromata, its activity being suppressed by an inhibitor adsorbed on the surface of the cells. Red blood cells exhibit proteolytic activity only after several washings with physiological saline solution.

Increased solubility of full blood clots in urea can be brought about by addition of an excess of active proteolytic factor (concentrated granulocyte or washed red blood cell suspensions) to the clot, or by prior washing of the clot with physiological saline (to remove the inhibitor). Noncellular clots (fibrin, plasma clots) may be dissolved in urea only after addition of granulocytes, platelets or activated red cells.

The possible role of this proteolytic activity in the in vivo liquefaction of blood clots is discussed.

Proteasome inhibitor MG-132 induces MCPIP1 expression

The proteasome is a protein complex responsible for the degradation of polyubiquitin-tagged proteins. Besides the removal of target proteins, the proteasome also participates in the regulation of gene transcription in both proteolytic and non-proteolytic fashion. In this study the effect of proteasome inhibition on the basal expression of monocyte chemotactic protein-1 induced protein 1 (MCPIP1) was examined. Treatment of HepG2 or HeLa cells with proteasome inhibitor MG-132 resulted in a significant increase of MCPIP1 expression, both at mRNA and protein level. Interestingly, MG-132 did not alter MCPIP1 stability. Instead, the observed protein increase was blocked by actinomycin D, suggesting the involvement of de novo mRNA synthesis in the increase of MCPIP1 protein following MG-132 treatment. Using several inhibitors we determined the participation of extracellular-signal-regulated kinase 1/2 and p38 kinases in MCPIP1 upregulation by MG-132. Our findings show for the first time the impact of proteasome inhibition on MCPIP1 protein expression by modulation of the activity of intracellular signaling pathways. Overexpression of MCPIP1-myc protein decreased the viability of HeLa cells but not HepG2 cells, which correlates with the increased susceptibility of HeLa cells to MG-132 toxicity. Notably, both MG-132 treatment and MCPIP1-myc overexpression led to the activation of apoptosis, as revealed by the induction of caspases 3/7 in both types of cell lines. This suggests the involvement of MCPIP1 upregulation in toxic properties of proteasome inhibition, which is an acknowledged approach to the treatment of several cancer types.

Rooperol, an inhibitor of cytokine synthesis, decreases the respiratory burst in human and rat leukocytes and macrophages

Luminol-enhanced chemiluminescence was measured in fresh whole human blood, or human neutrophils isolated from heparinized blood, human alveolar macrophages and rat alveolar macrophages stimulated with bacterial endotoxin (LPS). Tetraacetate esters of rooperol, a dicatechol showing anticytokine activity, added to cells simultaneously with LPS inhibited the respiratory burst. The effective concentrations of rooperol were in the range of 1-10 μM depending on cell type and corresponded well with inhibition of nitric oxide production by rat alveolar macrophages. Thus rooperol may reduce some effects of excessive phagocytic activity and inflammatory reaction but by quenching free radicals production may also diminish the resistance to bacterial infections.

Monocyte chemotactic protein-1-induced protein-1 (MCPIP1) is a novel multifunctional modulator of inflammatory reactions

The generalized inflammatory response leads to activation of hundreds of genes transcribed in an established sequence in specialized cells. Transcriptome analysis of human monocyte-derived cells stimulated with IL-1beta or with monocyte chemotactic protein-1 (MCP-1) has led to the identification of a new inflammation-related gene ZC3H12A encoding a chain of 599 amino acids corresponding to a 66-kDa protein. The protein, given a provisional name of MCPIP1 (monocyte chemotactic protein-induced protein-1), is expressed in several human and murine tissues such as bone marrow, spleen, heart and placenta. In in vivo studies, mice with inactivated MCPIP1-encoding gene showed growth retardation, lymphadenopathy, splenomegaly and enhanced inflammatory symptoms. Principal molecular features of MCPIP1 include a single zinc finger motif, an RNase-like PIN domain and ubiquitin-binding domain. Reports from independent laboratories suggest that MCPIP1 may function also as a deubiquitinase. Although MCPIP1 is regarded by some authors as a new transcription factor or cell differentiation factor modulating angiogenesis or adipogenesis, its principal function appears to be downregulation of inflammatory responses through at least two independent mechanisms: increased degradation of cytokine mRNAs and inhibition of LPS- and IL-1-induced NF-kappaB signaling pathway. The interference with NF-kappaB activation is highly complex and includes TRAF6 and TANK interaction with the ubiquitin-associated (UBA) domain of MCPIP1. Purified MCPIP1 protein was reported to degrade specific mRNA and cleave K48- and K63-linked polyubiquitin chains. Although some structural features and the mechanism of action of MCPIP1 are not fully explained yet, its importance in the regulation of inflammatory reactions has been firmly established.

Interleukin-1-inducible MCPIP protein has structural and functional properties of RNase and participates in degradation of IL-1beta mRNA

In human monocyte-derived macrophages, the MCPIP gene (monocyte chemoattractant protein-induced protein) is strongly activated by interleukin-1beta (IL-1beta). Using bioinformatics, a PIN domain was identified, spanning amino acids 130-280; such domains are known to possess structural features of RNases. Recently, RNase properties of MCPIP were confirmed on transcripts coding for interleukins IL-6 and IL-12p40. Here we present evidence that siRNA-mediated inhibition of the MCPIP gene expression increases the level of the IL-1beta transcript in cells stimulated with LPS, whereas overexpression of MCPIP exerts opposite effects. Cells with an increased level of wild-type MCPIP showed lower levels of IL-1beta mRNA. However, this was not observed when mutant forms of MCPIP, either entirely lacking the PIN domain or with point mutations in this domain, were used. The results of experiments with actinomycin D indicate that lower levels of IL-1beta mRNA are due to shortening of the IL-1beta transcript half-life, and are not related to the presence of AU-rich elements in the 3' UTR. The interaction of the MCPIP with transcripts of both IL-1beta and MCPIP observed in an RNA immunoprecipitation assay suggests that this novel RNase may be involved in the regulation of expression of several genes.

[Molecular mechanisms of the acute phase reaction and innate immunological response]

The acute phase reaction is currently regarded as systemic inflammatory response and a component of innate unspecific immunological reaction. This complex response is regulated mainly by cytokines - pleiotropic mediators of metabolic and immunological reactions. Among cytokines representing various protein families and participating in inflammation one can distinguish pro-inflammatory and anti-inflammatory cytokines as well as a large interleukin-6 family occupying intermediate position. In the initiation of acute phase reaction participate various components such as Toll-like receptors recognizing foreign pathogens, inflammasomes activating interleukin-1, and protein kinases from the MAP family that finally activate transcription factor NF-kappaB involved in cytokine synthesis. Secreted cytokines are recognized by receptors of target cells and switch on expression of many genes, including those coding for acute phase proteins. Regulation of acute phase response is precise and includes not only transcription and translation but also stability of mRNA and its degradation, as well as inhibitory activity of microRNA. Disturbances in the course of acute phase reaction are responsible for auto-immunological and autoimmune diseases and various pathological states such as acute septic shock or chronic arthritis. Some acute phase proteins, and especially C-reactive protein, have important implications for clinical diagnostics and preventive medicine.

Regulatory feedback loop between NF-kappaB and MCP-1-induced protein 1 RNase

A novel gene ZC3H12A, encoding MCP-1-induced protein 1 (MCPIP), was recently identified in human peripheral blood monocytes treated with monocyte chemotactic protein 1 (MCP-1) and in human monocyte-derived macrophages stimulated with interleukin (IL)-1beta. These experiments revealed that the gene undergoes rapid and potent transcription induction upon stimulation with proinflammatory molecules, such as MCP-1, IL-1beta, tumour necrosis factor alpha and lipopolysaccharide. Here we show that the induction of ZC3H12A by IL-1beta is predominantly NF-kappaB-dependent because inhibition of this signalling pathway results in the impairment of ZC3H12A transcription activation. Our results indicate the presence of an IL-1beta-responding region within the second intron of the ZC3H12A gene, which contains four functional NF-kappaB-binding sites. Therefore, we propose that this transcription enhancer transduces a ZC3H12A transcription-inducing signal after IL-1beta stimulation. Recent reports suggest that MCPIP acts as a negative regulator of inflammatory processes because it is engaged in the degradation of transcripts coding for certain proinflammatory cytokines. Our observations provide evidence for a novel negative feedback loop in the activation of NF-kappaB and point to potential significance of MCPIP in the treatment of various pathological states, such as diabetes or cancer that involve disturbances in the functioning of the NF-kappaB system.

Mimitin - a novel cytokine-regulated mitochondrial protein

BACKGROUND

The product of a novel cytokine-responsive gene discovered by differential display analysis in our earlier studies on HepG2 cells was identified as mimitin - a small mitochondrial protein. Since proinflammatory cytokines are known to affect components of the respiratory chain in mitochondria, and mimitin was reported as a possible chaperone for assembly of mitochondrial complex I, we looked for the effects of modulation of mimitin expression and for mimitin-binding partners.

RESULTS

By blocking mimitin expression in HepG2 cells by siRNA we found that mimitin has no direct influence on caspase 3/7 activities implicated in apoptosis. However, when apoptosis was induced by TNF and cycloheximide, and mimitin expression blocked, the activities of these caspases were significantly increased. This was accompanied by a slight decrease in proliferation of HepG2 cells. Our observations suggest that mimitin may be involved in the control of apoptosis indirectly, through another protein, or proteins. Using the yeast two-hybrid system and coimmunoprecipitation we found MAP1S among proteins interacting with mimitin. MAP1S is a recently identified member of the microtubule-associated protein family and has been shown to interact with NADH dehydrogenase I and cytochrome oxidase I. Moreover, it was implicated in the process of mitochondrial aggregation and nuclear genome destruction. The expression of mimitin is stimulated more than 1.6-fold by IL-1 and by IL-6, with the maximum level of mimitin observed after 18-24 h exposure to these cytokines. We also found that the cytokine-induced signal leading to stimulation of mimitin synthesis utilizes the MAP kinase pathway.

CONCLUSION

Mimitin is a mitochondrial protein upregulated by proinflammatory cytokines at the transcriptional and protein levels, with MAP kinases involved in IL-1-dependent induction. Mimitin interacts with a microtubular protein (MAP1S), and some changes of mimitin gene expression modulate activity of apoptotic caspases 3/7, suggesting that this protein may indirectly participate in apoptosis.

Identification of interleukin-1 and interleukin-6-responsive genes in human monocyte-derived macrophages using microarrays

The transcriptome profile of human monocyte-derived macrophages stimulated in vitro by low doses of IL-1 or IL-6 was analyzed by microarrays (Affymetrix, HG-U133A) in 5 independent experiments. Out of 4886 probe sets consistently detected in all 5 array replicates we found approximately 300 genes (FDR<5%) modulated by IL-1 and/or IL-6, among which 34 may be regarded as novel cytokine-responsive macrophage genes of various function. Detailed analysis indicates that cytokine-responsive genes include 125 transcripts significantly up-regulated by IL-1 and only 39 transcripts up-regulated by IL-6, whereas the number of down-regulated transcripts is lower and almost equal for both cytokines. These data indicate that, in comparison to liver cells, IL-1 is more potent than IL-6 in modulating gene expression of human macrophages. Hierarchical clustering analysis of these transcripts yielded 7 separate gene clusters. The most abundant group contains genes strongly activated by IL-1 alone and coding for chemokines, cytokines and their receptors, the components of intracellular signaling as well as transcription factors from NF-kB family. In order to validate the results obtained by microarray analysis the expression of 5 genes from various clusters was determined by quantitative RT-PCR. Moreover, the putative promoter regions of all cytokine-responsive genes were subjected to the in silico identification of transcription factor binding sites (TFBS). We found that TFBS corresponding to RelA/NF-kB is the most strongly over-represented group and we demonstrated involvement of NF-kB in the expression of selected genes.

Regulatory mechanisms of gene expression: complexity with elements of deterministic chaos

Linear models based on proportionality between variables have been commonly applied in biology and medicine but in many cases they do not describe correctly the complex relationships of living organisms and now are being replaced by nonlinear theories of deterministic chaos. Recent advances in molecular biology and genome sequencing may lead to a simplistic view that all life processes in a cell, or in the whole organism, are strictly and in a linear fashion controlled by genes. In reality, the existing phenotype arises from a complex interaction of the genome and various environmental factors. Regulation of gene expression in the animal organism occurs at the level of epigenetic DNA modification, RNA transcription, mRNA translation, and many additional alterations of nascent proteins. The process of transcription is highly complicated and includes hundreds of transcription factors, enhancers and silencers, as well as various species of low molecular mass RNAs. In addition, alternative splicing or mRNA editing can generate a family of polypeptides from a single gene. Rearrangement of coding DNA sequences during somatic recombination is the source of great variability in the structure of immunoglobulins and some other proteins. The process of rearrangement of immunoglobulin genes, or such phenomena as parental imprinting of some genes, appear to occur in a random fashion. Therefore, it seems that the mechanism of genetic information flow from DNA to mature proteins does not fit the category of linear relationship based on simple reductionism or hard determinism but would be probably better described by nonlinear models, such as deterministic chaos.

Identification of major cellular proteins synthesized in response to interleukin-1 and interleukin-6 in human hepatoma HepG2 cells

Interleukin-1 (IL-1) and interleukin-6 (IL-6) are principal proinflammatory cytokines inducing the acute phase response of various tissues, including liver. Cultured human hepatoma HepG2 cells were stimulated with IL-1 (10 ng/ml) and IL-6 (10 ng/ml). After 24 h the cells were collected and disrupted by sonication in a lysis buffer containing 8M urea. The extracted cellular proteins were separated by 2D polyacrylamide gel electrophoresis. The gels were stained with Coomassie Brilliant Blue R-250 and the protein spots showing different intensities in comparison to control (unstimulated) cells were excised and subjected to analysis by LC-MS/MS. Alternatively, proteins were stained with SYPRO Ruby. These differentially expressed proteins include seven up-regulated and two down-regulated intracellular proteins of various functions. The identification of three cytokine-responsive proteins was confirmed by biosynthetic labeling with [35S]methionine after incubation of HepG2 cells, and by western blot with specific antisera.

Regulatory mechanisms of gene expression: complexity with elements of deterministic chaos

Linear models based on proportionality between variables have been commonly applied in biology and medicine but in many cases they do not describe correctly the complex relationships of living organisms and now are being replaced by nonlinear theories of deterministic chaos. Recent advances in molecular biology and genome sequencing may lead to a simplistic view that all life processes in a cell, or in the whole organism, are strictly and in a linear fashion controlled by genes. In reality, the existing phenotype arises from a complex interaction of the genome and various environmental factors. Regulation of gene expression in the animal organism occurs at the level of epigenetic DNA modification, RNA transcription, mRNA translation, and many additional alterations of nascent proteins. The process of transcription is highly complicated and includes hundreds of transcription factors, enhancers and silencers, as well as various species of low molecular mass RNAs. In addition, alternative splicing or mRNA editing can generate a family of polypeptides from a single gene. Rearrangement of coding DNA sequences during somatic recombination is the source of great variability in the structure of immunoglobulins and some other proteins. The process of rearrangement of immunoglobulin genes, or such phenomena as parental imprinting of some genes, appear to occur in a random fashion. Therefore, it seems that the mechanism of genetic information flow from DNA to mature proteins does not fit the category of linear relationship based on simple reductionism or hard determinism but would be probably better described by nonlinear models, such as deterministic chaos.

A search for genes modulated by interleukin-6 alone or with interleukin-1beta in HepG2 cells using differential display analysis

Interleukin-1 and interleukin-6 are principal cytokines involved in regulation of expression of acute-phase proteins. In the joint action of both cytokines IL-1 can suppress or enhance the IL-6-dependent induction of gene expression. Here, we report changes in the transcriptome profile of HepG2 cells exposed to IL-6 alone, or IL-1 and IL-6. Cytokine-responsive genes were identified by differential display analysis. Validation of observed changes in the transcript level was carried out using the slot blot method. Out of 88 cDNA species modulated by IL-6, only 38 represent different known genes whereas 18 clones match genomic clones in NCBI data with hypothetical cDNA sequences (the remaining 32 clones showed no homology with the database or represented several clones of the same gene). In the experiments with HepG2 cells prestimulated for 3 h with IL-1 and then stimulated with IL-6, 43 cDNA fragments were amplified. Twenty-three of them represent known genes while 10 clones have inserts matching hypothetical cDNA sequences in NCBI data. The identified transcripts modulated by IL-6 or both cytokines in HepG2 cells code for intracellular proteins of various function. The largest groups represent genes engaged in metabolism, protein synthesis and signaling pathways. Among all genes identified as differentially regulated under stimulation by IL-6, or IL-1/IL-6, six were detected in both types of stimulation. None of the typical genes coding for plasma acute phase proteins was identified in our experiments. This indicates that differential display cannot be used to characterize the profile of a given transcriptome. On the other hand, it is a useful technique for detection of new genes responding to IL-6 alone or IL-6 in combination with IL-1.

Transcription factors as targets of the anti-inflammatory treatment. A cell culture study with extracts from some Mediterranean diet plants

During the inflammatory response at least 2 transcription factors, NF-kappaB and AP-1, are involved in the altered profile of gene expression. We used human hepatoma (HepG2) and human umbilical vein endothelial cells (HUVEC) as a model system: NF-kappaB and AP-1 were activated by the proinflammatory cytokine IL-1 in the absence or presence of 21 selected plant extracts and the effect was evaluated by the electrophoretic mobility shift assay (EMSA). In both types of cells activation of NF-kappaB by IL-1 was significantly inhibited by extracts from Scandix australis and Artemisia alba, whereas extracts from Amaranthus sp., Eryngium campestre, Thymus pulegioides and Reichardia picroides elicited cell-type dependent response. The IL-1-induced AP-1 activation was diminished by extracts from Scandix australis, Amaranthus sp. and Artemisia alba more potently in HUVEC, while extracts from Urospermum picroides and Scandix pecten-veneris in HepG2 cells. Inhibitory activities of plant extracts towards cytokine activated NF-kappaB and AP-1 depend to some extent on the order of addition of IL-1 and plant extract to the cell culture, but the mechanism of action of extract components is not clear: although plant polyphenols may participate they are unlikely to be the only mediators, and MAP kinases were found generally not involved in down-regulation of transcription factors activity by plant extracts.

Identification of changes in the transcriptome profile of human hepatoma HepG2 cells stimulated with interleukin-1 beta

Interleukin-1 (IL-1) is the principal pro-inflammatory cytokine participating in the initiation of acute phase response. Human hepatoma HepG2 cells were exposed to 15 ng/ml of IL-1beta for times ranging from 1 to 24 h and the total RNA was isolated. Then cDNA was obtained and used for differential display with 10 arbitrary primers and 9 oligo(dT) primers designed by Clontech. Validation of observed changes of differentially expressed known genes was carried out by RT-PCR or Northern blot analysis. Out of 90 cDNA strands modulated by IL-1, 46 have been successfully reamplified and their sequencing indicates that they represent 36 different cDNA templates. By GenBank search, 26 cDNA clones were identified as already known genes while 10 showed no homology to any known gene. The identified transcripts modulated by IL-1 in HepG2 cells code for intracellular proteins of various function: trafficking/motor proteins (3 genes), proteins participating in the translation machinery or posttranscriptional/posttranslational modifications (7 genes), proteases (1 gene), proteins involved in metabolism (6 genes), activity modulators (3 genes), proteins of the cell cycle machinery (2 genes) and those functionally unclassified (4 genes). Majority of genes responded to IL-1 within 1 to 6 h (early genes), while two were late response genes (12-24 h) and four showed prolonged response over the whole 24-h period. Most of the observed changes of expression were in the range of two- to threefold increase in comparison to control untreated cells. Among identified genes, no typical secretory acute phase protein was found. The obtained results suggest that IL-1 affects the expression of several genes in HepG2 cells, especially those engaged in the synthesis and modifications of proteins.

Regulation of expression of stromyelysin-1 by proinflammatory cytokines in mouse brain astrocytes

Stromelysin-1 belongs to matrix metalloproteinases responsible for proteolytic degradation of extracellular matrix in many tissues during various diseases, especially those involving inflammation. We studied the induced expression of stromelysin-1 in primary cultures of mouse brain astrocytes stimulated with various cytokines and cellular growth factors. Interleukin-1-beta (IL-1beta), tumor necrosis factor alpha (TNFalpha) and a mixture of IL-1, TNF and epidermal growth factor (EGF) significantly increased the level of stromelysin-1 mRNA in mouse astrocytes while interferon-gamma (IFN-gamma) inhibited this response or was without effect. This accumulation of specific mRNA was preceded by activation of two examined transcription factors: NFkappaB and AP-1. However, experiments with known inhibitors of activation of these transcription factors: pyrrolidine dithiocarbamate (PDTC), parthenolide and curcumin, indicate that NFkappaB and AP-1 cannot be solely responsible for the cytokine induced expression of stromelysin-1 gene in mouse astrocytes.

Complex analysis of genes involved in the inflammatory response: interleukin-1-induced differential transcriptome of cultured human hepatoma HepG2 cells

The systemic inflammatory reaction (acute phase response) is induced by many noxious stimuli but in all cases the inflammatory cytokines, such as interleukin-1-beta (IL-1beta) and interleukin-6 (IL-6), are involved. Liver cell response to inflammation manifested by a characteristic change in the profile of synthesized plasma proteins (acute phase proteins) has been extensively studied. Here we describe a model system of cultured human hepatoma HepG2 cells stimulated with IL-1beta to evaluate the transcriptome induced by this cytokine during 24 h of treatment. By using differential display analysis we found IL-1beta-induced upregulation of several genes coding for cellular trafficking/motor proteins, proteins participating in the translation machinery or involved in posttranscription/posttranslation modifications, proteases, proteins involved in cellular metabolism, activity modulators, proteins of the cell cycle machinery and also some new proteins so far functionally not classified.

IL-1-mediated inhibition of IL-6-induced STAT3 activation is modulated by IL-4, MAP kinase inhibitors and redox state of HepG2 cells

It is known that during acute phase reaction IL-6 activates STAT3 in hepatoma cells and IL-1 downregulates this response. We found that the inhibitory properties of IL-1 on STAT signalling cascade in human hepatoma HepG2 cells are considerably decreased not only in the presence of MAP kinase inhibitors SB203580 and PD98059 but also by some antioxidants (N-acetyl cysteine and pyrrolidine dithiocarbamate) and by anti-inflammatory cytokine IL-4. It appears that cytokine crosstalk between IL-6 and IL-1 includes a direct pathway sensitive to antioxidants and MAP kinase inhibitors, whereas the indirect prolonged response depends probably on synthesis of suppressors of cytokine signalling (SOCS).

Complex analysis of genes involved in the inflammatory response: interleukin-1-induced differential transcriptome of cultured human hepatoma HepG2 cells

The systemic inflammatory reaction (acute phase response) is induced by many noxious stimuli but in all cases the inflammatory cytokines, such as interleukin-1-beta (IL-1beta) and interleukin-6 (IL-6), are involved. Liver cell response to inflammation manifested by a characteristic change in the profile of synthesized plasma proteins (acute phase proteins) has been extensively studied. Here we describe a model system of cultured human hepatoma HepG2 cells stimulated with IL-1beta to evaluate the transcriptome induced by this cytokine during 24 h of treatment. By using differential display analysis we found IL-1beta-induced upregulation of several genes coding for cellular trafficking/motor proteins, proteins participating in the translation machinery or involved in posttranscription/posttranslation modifications, proteases, proteins involved in cellular metabolism, activity modulators, proteins of the cell cycle machinery and also some new proteins so far functionally not classified.

Mechanism of plasminogen activator inhibitor-1 regulation by oncostatin M and interleukin-1 in human astrocytes

Glial cells that produce and respond to various cytokines mediate inflammatory processes in the brain. Here, we show that oncostatin M (OSM) and interleukin-1 (IL-1) regulate the expression of plasminogen activator inhibitor-1 (PAI-1) and urokinase-type plasminogen activator (uPA) in human astrocytes. Using the PAI-1 reporter constructs we show that the -58 to -51 proximal element mediates activation by both cytokines. This element is already bound by c-fos/c-jun heterodimers in unstimulated astrocytes, and treatment with cytokine strongly stimulates both expression of c-fos and binding of c-fos/c-jun heterodimers. In addition, IL-1 activates an inhibitory mechanism that down-regulates PAI-1 expression after longer exposure to this cytokine. Overexpression of dominant-negative signal transducer and activator of transcription-1 (STAT1), STAT3, STAT5 and inhibitor of nuclear factor-kappaB (IkappaB) suppressed OSM/IL-1-induced expression of the PAI-1 reporter construct. We conclude that OSM and IL-1 regulate the PAI-1 gene expression via up-regulating c-fos levels and subsequent binding of c-fos/c-jun heterodimers to the proximal element of the PAI-1 gene.

Cytokines regulate plasminogen activation system in astrocytoma cells

We report here that human astrocytoma cell line U373-MG is able to express genes of the following components of plasminogen activation system: PA1-1, PN-1, u-PA and t-PA. Treatment of these cells with IL-1beta results in accumulation of PA1-1, PN-1 and u-PA mRNAs, whereas t-PA mRNA remains unaffected. IFNy preferentially enhances PN-1 and PA1-1, EGF enhances PA1-1, u-PA and t-PA expression. Simultaneous addition of anti-inflammatory cytokines IL-4, IL-13 and IL-10 has little effect on the tested components, except induction of u-PA mRNA wich was further enhanced by IL-4. We have confirmed interesting time-dependent regulation of plasminogen activation system by EGF/IFNgamma. Cells stimulated with EGF/IFNgamma show at first increased proteolytic activity but after 24 h inhibition of proteolysis with PA1-1 would prevail. To understand the cooperative effect of EGF and IFNgamma in PA1-1 induction the kinetics of activation of STAT1 was studied. It was found that although EGF alone does not activate STAT1, the STAT1 binding activity in the cells treated with the mixture of EGF/IFNgamma was considerably prolonged. Our results indicate the importance of inflammatory cytokines and EGF in gene regulation of plasminogen activation system in astrocytoma cells.

Epidermal growth factor and pro-inflammatory cytokines regulate the expression of components of plasminogen activation system in U373-MG astrocytoma cells

Cytokines and growth factors that influence both secretion of the extracellular matrix (ECM) proteins and migration of the cells decide about the final outcome of tissue remodelling. We have examined expression of the components of the plasminogen activation system in human astrocytoma U373-MG cells and found that interleukin 1beta (IL-1beta), tumour necrosis factor alpha TNF-alpha), interferon gamma (INF-gamma) and epidermal growth factor (EGF) specifically regulate the expression of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), plasminogen activator inhibitor type 1 (PAI-1) and protease nexin-1 (PN-1). We conclude that EGF and IFN-gamma are new important regulators of the plasminogen activation system in astrocytoma cells and, therefore, may influence turnover of extracellular matrix and migration of cells within the brain.

Differential effects of oncostatin M and leukaemia inhibitory factor expression in astrocytoma cells

The effects of the production of two closely related cytokines, oncostatin M (OSM) and leukaemia inhibitory factor (LIF), by astrocytoma cells were investigated using the stable cell line human U373-MG, which expressed and secreted both biologically active polypeptides. The expression of LIF by these cells caused resistance to this cytokine due to loss of the LIF receptor (LIFR), from the cell surface, suggesting its retention. In contrast, cells expressing OSM were stimulated by this cytokine, utilizing an autocrine mechanism, and possessed receptors for OSM, but not LIF, on the cell surface. In these cells the continuous up-regulation of OSM-induced gene expression was found even though the Janus kinase-signal transducer and activator of transcription ('JAK/STAT') pathway was almost exhausted due to long-term autocrine stimulation of the cells by OSM. The amount of LIFR was down-regulated in both LIF- and OSM-producing cells and this effect was not found in wild-type U373-MG cells treated with externally added cytokines. To investigate the mechanism of autocrine stimulation by OSM we constructed a stable cell line expressing a form of OSM that is retained in the endoplasmic reticulum (ER). This biologically active cytokine was not secreted, but was localized in the ER. In addition, it did not stimulate the astrocytoma cells in an autocrine manner. We conclude that expression of LIF causes resistance of astrocytoma cells to this cytokine, whereas expression of OSM leads to autocrine stimulation.

Differential responses of hematopoietic and non-hematopoietic cells to anti-inflammatory cytokines: IL-4, IL-13 and IL-10

Recombinant preparations of human anti-inflammatory cytokines: IL-4, IL-13 and IL-10, inhibited LPS-induced synthesis of TNFalpha and IL-6 in the whole human blood tested in vitro. These cytokines also inhibited LPS-induced IL-6 and TNF mRNA accumulation in isolated human blood monocytes/macrophages. On the other hand, similar concentrations of IL-4 and IL-13 (but not IL-10) enhanced synthesis of IL-6 in cultured human umbilical vein endothelial cells (HUVEC). In human hepatoma HepG2 cells IL-4 and IL-13 (but not IL-10) inhibited IL-6-induced synthesis of haptoglobin. These differential responses to the tested anti-inflammatory cytokines were observed at mRNA and protein levels and may reflect cell specificities in signalling pathways and gene expression. When HUVEC and HepG2 cells were cultured together and stimulated with LPS the addition of IL-4 or IL-13 resulted in the reduction of LPS-induced and IL-6-mediated haptoglobin synthesis. Thus in co-culture the inhibitory effects of IL-4 or IL-13 on HepG2 cells prevail over stimulation of IL-6 synthesis in HUVEC.

Termination of acute-phase response: role of some cytokines and anti-inflammatory drugs

1. The acute-phase response is triggered by changes in intracellular mediators that activate stress-sensitive kinases and transcription factors controlling the synthesis of proinflammatory cytokines such as TNF-alpha, IL-1, IL-8 or IFN-gamma. 2. Natural extinguishing of acute-phase response occurs due to short half-lives of inflammatory mediators and production of anti-inflammatory cytokines such as IL-10, IL-4, IL-13, TGF-beta and some others. 3. Excess proinflammatory cytokines are removed by soluble cytokine receptors and receptor antagonists. 4. Synthesis of proinflammatory mediators and cytokines can be blocked by glucocorticoids, some nonsteroidal anti-inflammatory drugs suppressing cyclooxygenase and by specific inhibitors of cytokine induction. 5. The most promising approach in effective termination of acute-phase response appears to be a combined use of anti-inflammatory cytokines and specific drugs.

Vaccinia virus-induced changes in cytokine-regulated acute phase plasma protein synthesis by hepatoma cells

Human hepatoma cell line, HepG2, has been infected with vaccinia virus and synthesis of plasma proteins was determined by electroimmunoassay and corresponding mRNA's measured by Northern blotting. The inhibitory effect of the virus was dose- and time-dependent. Electrophoretic mobility shift assay revealed a decrease in C/EBP binding activities in nuclear extracts isolated from the infected hepatoma cells. Supershift analysis of the C/EBP isoforms showed alpha and beta subunit involvement in DNA binding. The treatment of the cells with interleukin-1, interleukin-6, and dexamethasone at the initial stage of infection appears to delay the virally induced inhibition of host cell protein synthesis. Thus, possible "protective" role of the acute phase cytokines in viral infection is proposed.

Vaccinia virus-regulated acute phase cytokine production in human fibroblasts, U937 cells and endothelium

The production of acute phase cytokines, interleukin 6 (IL-6), tumour necrosis factor (TNFalpha) and interleukin 1 (IL-1beta), was studied in primary cultures of human skin fibroblasts, human monocytic cell line U937 and primary cultures of human umbilical vein endothelial cells (HUVEC) after in vitro infection with vaccinia virus. Significant increase in IL-6 mRNA followed by enhanced protein secretion into the culture media was found in fibroblasts, U937 cells, and HUVEC. TNFalpha increased production in vaccinia virus infected U937 cells resembled closely the pattern of IL-6 production observed in the infected cells. Transient increase in NF-kappaB binding activity was found in the infected U937 (at 90 min) and endothelial (at 30 min) cells. Vaccinia virus induced cytokine production appeared to be transcriptional.

Rooperol tetraacetate decreases cytokine mRNA levels and binding capacity of transcription factors in U937 cells

We have previously described inhibition of the synthesis of three acute-phase inflammatory cytokines in human and rat macrophages by acetate esters of rooperol, a dicatechol of plant origin. Analysing the mechanism of anticytokine activity of rooperol, we compared levels of TNFalpha, IL-1beta and IL-6 mRNAs in the human promonocytic U937 cell line pretreated with phorbol myristate acetate (PMA) and incubated with rooperol tetraacetate (RTA) alone or in combination with LPS (500 ng/ml). It was found that 10 microM RTA decreased the levels of cytokine mRNAs both in the presence and absence of LPS, suggesting pretranslational inhibition of cytokine synthesis. Electrophoretic mobility shift analysis (EMSA) showed that RTA may influence cytokine mRNA expression by decreasing the binding activity of transcription factors NF-kappaB and AP-1.

Inhibitory effect of di-catechol rooperol on VCAM-1 and iNOS expression in cytokine-stimulated endothelium

Induced expression of vascular cell adhesion molecule-1 (VCAM-1) and of nitric oxide synthase (iNOS) is believed to play a role in the pathogenesis of atherosclerosis, asthma, as well as other inflammatory disorders. In the current study we examined the effect of the di-catechol rooperol [(E)-1,5-bis (3',4'-dihydroxyphenyl) pent-4-en-1-yne] on the process of microvascular endothelial cell (MME) activation by TNF-alpha and IFN-gamma. We show that rooperol decreases VCAM-1 and iNOS mRNA levels in cytokine-activated MME with subsequent inhibition of VCAM-1 membrane expression as measured by adhesion of P815 cells to MME monolayers, and NO production, as reflected in the nitrite concentration in culture medium. The properties of rooperol now described suggest that rooperol may be an anti-inflammatory agent useful in the treatment of several inflammatory disorders.

Initiation of acute phase response and synthesis of cytokines

A variety of injuries, such as bacterial infection or ischemic tissue necrosis, induce systemic acute phase reaction expressed as fever, leukocytosis, release of several hormones, activation of clotting, complement and kinin forming pathways, and drastic increase of synthesis of certain plasma proteins. The reaction is triggered by 'alarm molecules', including free radicals, which activate several stress-sensitive protein kinases (ERK, p38, JNK) in macrophages and other responsive cells. These kinases phosphorylate, usually in a multi-step cascade, transcription factors belonging primarily to C/EBP, NF-kappa B and AP-1 families. Active transcription factors after translocation to nucleus interact with responsive elements in the gene promoters of acute-phase cytokines: tumor necrosis factor-alpha, interleukin-1 and interleukin-6. Enhanced transcription of these genes is usually followed by rapid translation and precursor protein processing leading to the release of biologically active cytokines. Fine tuning of the acute phase response appears to be regulated at all stages: primary signals, kinase cascades, transcription factors, mRNA stability and translation, cytokine precursor processing, secretion and bioavailability. This makes possible designing of specific inhibitors of cytokine synthesis as potential therapeutic drugs.

Cytokine production in human and rat macrophages and dicatechol rooperol and esters

The ability of dicatechol rooperol and esters to inhibit the production of cytokines in endotoxin-stimulated human alveolar macrophages, human blood monocyte/macrophages, histiocytic cell line U937, and rat alveolar macrophages was examined in vitro. Rooperol derivatives inhibited the production of tumour necrosis factor-alpha, interleukin-1 beta and interleukin-6. Of the esters tested on human cells, rooperol diacetate and tetraacetate were more potent inhibitors of cytokine production (IC50 in the range of 10-20 microM) than rooperol disulphate (IC50 in the range of 25-75 microM). The acetate esters also inhibited cytokine production in rat alveolar macrophages, whereas the sulphate had little effect. Rooperol and acetate esters, in the same concentration range, decreased the production of nitric oxide by rat alveolar macrophages stimulated by endotoxin. These concentrations of rooperol had no effect on cell viability, as indicated by incorporation of 14C-labelled leucine into macrophage proteins and their content of lactate dehydrogenase. The results obtained suggest that rooperol esters are potentially useful antiinflammatory agents.

Identification of the interleukin-6/oncostatin M response element in the rat tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter

The rat tissue inhibitor of metalloproteinase 1 (TIMP-1) gene is expressed in rat hepatocytes, and this expression is up-regulated by interleukin 6 (IL-6). We report here the cloning of the 5' flanking region of the rat TIMP-1 gene and identification of an IL-6/oncostatin M (OSM) response element at -64 to -36 which functions in hepatic cells. Within this element we have identified two functional binding sites for transcription factors AP-1 (activatory protein-1) and STAT (signal transducer and activator of transcription). IL-6/OSM stimulation induces binding of a protein, identified as STAT3, to the IL-6/OSM response element, while binding of the AP-1 protein was constitutive. Binding sites for both AP-1 and STAT3 are necessary for full responsiveness of the TIMP-1 promoter to IL-6/OSM, as shown by deletion and mutation analysis. Furthermore, the entire IL-6/OSM response element conferred responsiveness onto a heterologous promoter, whereas this has not been observed when AP-1 and STAT elements were separately tested.

Expression of a biologically active murine tissue inhibitor of metalloproteinases-1 (TIMP-1) in baculovirus-infected insect cells. Purification and tissue distribution in the rat

Murine tissue inhibitor of metalloproteinases-1 (mTIMP-1) was expressed in baculovirus-infected insect cells (Sf9). The protein secreted into the culture medium was purified to homogeneity by means of heparin-Sepharose CL-6B and FPLC. The purified protein showed metalloproteinase-inhibitory activity in two independent assays: reverse zymography and inhibition of collagenase activity. Digestion of the recombinant TIMP-1 with peptide-N-glycanaseF revealed that both N-glycosylation sites are used. 125I-mTIMP-1 intraveneously injected into a male Sprague Dawley rat disappeared within 2 min from the circulation. 5 min after injection more than 50% of the 125I-mTIMP-1 were found in the liver and 20% in the kidneys. At later times, trichloroacetic-acid-soluble material accumulated in the intestinal tract.

Hepatocyte growth factor and retinoic acid exert opposite effects on synthesis of type 1 and type 2 acute phase proteins in rat hepatoma cells

Rat hepatoma cells H-35 cultured in serum-free medium were exposed to interleukin-6 (IL-6), interleukin-1 (IL-1), hepatocyte growth factor (HGF), retinoic acid (RA), or a mixture of these factors. Production of acute phase proteins, responding to IL-6 alone (type 2) or to the mixture of IL-6 and IL-1, was assessed by electroimmunoassay and the corresponding mRNAs were compared by Northern blot analysis. HGF enhanced IL-6-induced synthesis of alpha-2-macroglobulin but reduced synthesis of C3 complement and alpha-1-acid glycoprotein. Retinoic acid reduced the response to IL-6 of alpha-2-macroglobulin but enhanced that of alpha-1-acid glycoprotein and especially of C3 complement. In general, changes in protein secretion were correlated with the contents of their corresponding cellular mRNAs. These results indicate that hepatocyte growth factor can enhance basal or IL-6-induced gene expression of type 2 and reduce the expression of type 1 acute phase proteins, whereas the action of retinoic acid is opposite. The modulation of acute phase response by HGF and RA likely involves transcriptional factors and regulatory sequences in the genes coding for these two types of acute phase proteins.

Long-term culture of HepG2 hepatoma cells as a model for liver acute phase response during chronic inflammation. Effects of interleukin-6, dexamethasone and retinoic acid

HepG2 cells were cultured for 7 days in serum-free medium in the presence of interleukin-6 (IL-6), retinoic acid (RA) or dexamethasone (DX), and some plasma proteins secreted to the media were determined by electroimmunoassay whereas the contents of specific mRNAs in the cells was evaluated by Northern blot hybridization. Interleukin-6 maximally stimulated synthesis of alpha-1-antichymotrypsin between days 1 and 3 whereas the response of fibrinogen was delayed to days 3 to 7. Retinoic acid increased the effect of IL-6 on alpha-1-antichymotrypsin (ACT) and fibrinogen (FBG) on the level of both proteins and mRNAs. Synthesis of albumin was slightly inhibited by IL-6 and RA, and synthesis of transferrin was increased by RA but not by IL-6. Dexamethasone had small enhancing effect on the action of IL-6. These results suggest that long-term HepG2 cultures may provide an experimental model for liver acute phase response during chronic inflammation.

Insulin cooperates with IL-1 in regulating expression of alpha 1-acid glycoprotein gene in rat hepatoma cells

Insulin treatment of the rat hepatoma H-35 cells results in a reduced stimulation of acute phase plasma protein gene expression by IL-1- and IL-6-type cytokines. The cell response to insulin appears to involve both stimulatory and inhibitory regulatory mechanisms because a clonal variant line of the H-35 cells has been identified in which insulin increases specifically the IL-1 stimulation of alpha 1-acid glycoprotein (AGP) gene, while still reducing the expression of the other acute phase protein genes. The magnitude of insulin and cytokine effect is dependent upon the proliferation state of the cell culture. One of the genetic targets of the insulin stimulation has been located to the cytokine-response element of the AGP gene and involves a cooperativity with the 5' adjacent IL-1-responsive element. The molecular mechanism of insulin inhibition, however, remains to be identified.

Rat contrapsins are the type II acute phase proteins: regulation by interleukin 6 on the mRNA level

Three highly homologous serine protease inhibitors, SPI-1, SPI-2 and SPI-3 (contrapsins), are synthesized in rat liver. Their expression is regulated differently in healthy and inflamed animals. We found that interleukin 6 (IL-6), a major acute phase cytokine, and to a lesser extent leukemia inhibitory factor (LIF), both together with glucocorticoids, are responsible for the regulation of expression of the contrapsins in rat hepatocytes in primary culture. The effect of IL-6 is time- and dose-dependent. IL-1, TGF beta 1, HGF, PMA and IL-8 did not have any effect on contrapsin mRNA levels. We postulate that SPI-1, SPI-2 and SPI-3 belong to the class II acute phase proteins. Additionally, we show induction of SPI-3 mRNA in rat liver by in situ hybridization using a specific oligonucleotide probe.

Origin of circulating acute phase cytokines: modified proteins may trigger IL-6 production by macrophages. Preliminary report

Human peripheral blood monocytes isolated by centrifugation with Mono-Poly resolving medium, and human alveolar macrophages obtained by lung lavage during fiberoscopic bronchoscopy, were cultured in RPMI containing 2% foetal calf serum. The cultures were exposed to modified human proteins: alpha-1-antitrypsin cleaved with papain, fibrinogen degradation products (fraction D) purified from plasmin digest, and non-enzymatically glycosylated (glycated) serum albumin. Conditioned macrophage media were tested for the contents of acute phase cytokines by bioassay with hepatoma cells, and the concentration of interleukin-6 was determined with ELISA. Modified proteins stimulated macrophages to produce acute phase cytokines and the response was not abrogated by polymyxin B in distinction to stimulation of macrophages by endotoxin. Our data indicate that some proteolytically damaged proteins or the end glycosylation products formed in pathological states (acute inflammation, diabetes) may be responsible for the appearance of cytokines in the circulation.

Divergent transforming growth factor-beta effects on IL-6 regulation of acute phase plasma proteins in rat hepatoma cells

The rat hepatoma cell line, H-35, responds to IL-1- and IL-6-type cytokines by an increased transcription of specific acute phase plasma protein (APP) genes. Transforming growth factor-beta (TGF-beta), although ineffective on its own in regulating APP genes, modulates the action of the IL-type cytokines. In growing cultures, the IL-6 and IL-11 stimulation of thiostatin and hemopexin is enhanced by TGF-beta, whereas the stimulation of other APP is reduced. The effects of leukemia inhibitory factor, ciliary neurotrophic factor, IL-1, and TNF-alpha are generally attenuated by TGF-beta. Enhancement by TGF-beta of the IL-6-induced response can be explained in part by the fact that TGF-beta, in combination with dexamethasone, stimulates severalfold the expression of the 80-kDa ligand-binding subunit of IL-6R. Serum deprivation of H-35 cells for 3 days leads to an enhanced basal and cytokine-stimulated level of APP gene expression concomitant with a loss of the divergent regulatory effect of TGF-beta. In growth-arrested H-35 cells, TGF-beta still enhances the IL-6R expression but it attenuates all IL-6 effects on APP genes. These data suggest that TGF-beta influences the signal transduction of the IL-type cytokines by separate mechanisms and that the manifestation of the TGF-beta action is modulated by the growth state of the cell culture.

Divergent transforming growth factor-beta effects on IL-6 regulation of acute phase plasma proteins in rat hepatoma cells

The rat hepatoma cell line, H-35, responds to IL-1- and IL-6-type cytokines by an increased transcription of specific acute phase plasma protein (APP) genes. Transforming growth factor-beta (TGF-beta), although ineffective on its own in regulating APP genes, modulates the action of the IL-type cytokines. In growing cultures, the IL-6 and IL-11 stimulation of thiostatin and hemopexin is enhanced by TGF-beta, whereas the stimulation of other APP is reduced. The effects of leukemia inhibitory factor, ciliary neurotrophic factor, IL-1, and TNF-alpha are generally attenuated by TGF-beta. Enhancement by TGF-beta of the IL-6-induced response can be explained in part by the fact that TGF-beta, in combination with dexamethasone, stimulates severalfold the expression of the 80-kDa ligand-binding subunit of IL-6R. Serum deprivation of H-35 cells for 3 days leads to an enhanced basal and cytokine-stimulated level of APP gene expression concomitant with a loss of the divergent regulatory effect of TGF-beta. In growth-arrested H-35 cells, TGF-beta still enhances the IL-6R expression but it attenuates all IL-6 effects on APP genes. These data suggest that TGF-beta influences the signal transduction of the IL-type cytokines by separate mechanisms and that the manifestation of the TGF-beta action is modulated by the growth state of the cell culture.

Molecular cloning and expression of an intracellular serpin: an elastase inhibitor from horse leucocytes

Horse blood leucocytes contain an elastase inhibitor (HLEI) belonging to the serpin family. Poly(A)+RNA isolated from these cells was used to construct a cDNA library in lambda gt10, which was first screened with a synthetic degenerate oligonucleotide probe corresponding to the amino acid sequence of the reactive centre of the inhibitor. Three clones were obtained covering the entire coding region of the protein. Sequencing of these clones showed identity with the amino acid sequence obtained from Edman degradation of the elastase inhibitor. The coding sequence of the HLEI cDNA was cloned into the bacterial expression vector pKK233-2 and expressed in Escherichia coli cells. Transformed bacteria expressed significant amounts of the protein, which was immunoprecipitated with a specific anti-HLEI antiserum. Furthermore, HLEI expressed in bacteria inhibited the activity of elastase but not trypsin.

Regulation of synthesis of some proteinase inhibitors in human hepatoma cells HepG2 by cytokines, hepatocyte growth factor and retinoic acid

Subconfluent monolayers of human hepatoma HepG2 cells were cultured for 2 days in serum-free DMEM containing 1 microM dexamethasone and human recombinant hepatocyte growth factor (HGF), retinoic acid (RA), IL-1, IL-6, LIF and mixtures of these factors. Incorporation of labelled thymidine was significantly decreased by IL-6, IL-1 and HGF but only slightly by LIF and RA. Synthesis of acute phase proteins secreted daily to the media was measured by electroimmunoassay with monospecific antisera. In addition, the synthesis and secretion of some proteinase inhibitors (alpha-1-proteinase inhibitor, alpha-1-antichymotrypsin, C1-inactivator, plasminogen activator inhibitor-1, inter-alpha-trypsin inhibitor and pre-alpha-inhibitor) was evaluated by incorporation of labelled methionine and fluorography. Among the cytokines tested IL-6 was the most potent regulator of acute phase protein synthesis. Hepatocyte growth factor stimulated basal synthesis of alpha-1-antichymotrypsin, and to a lesser extent affected some other proteins. Retinoic acid preferentially increased synthesis of alpha-1-antichymotrypsin, ceruloplasmin and plasminogen activator inhibitor-1. Both HGF and RA slightly modulated cytokine-induced synthesis of several acute phase proteins in HepG2 cells.

Synthesis of tissue inhibitor of metalloproteinase-1 (TIMP-1) in human hepatoma cells (HepG2). Up-regulation by interleukin-6 and transforming growth factor beta 1

Metalloproteinases and their specific inhibitors, believed to play a role in extracellular matrix metabolism, are regulated by inflammatory cytokines. Here we have addressed the question of whether liver, the major site of synthesis of plasma proteinase inhibitors, is also capable of synthesizing the tissue inhibitor of metalloproteinase-1 (TIMP-1). We show at mRNA and protein levels that TIMP-1 is expressed in differentiated human hepatoma cells (HepG2) and that its synthesis is up-regulated by interleukin-6 (IL-6), transforming growth factor beta 1 and phorbol 12-myristate 13-acetate. The physiological role of this phenomenon is underlined by the fact that lipopolysaccharide administration into rats in vivo, as well as IL-6-stimulation of rat hepatocytes in primary culture, also leads to an increase of TIMP-1 mRNA in liver cells.

Synthesis of alpha 1-microglobulin in cultured rat hepatocytes is stimulated by interleukin-6, leukemia inhibitory factor, dexamethasone and retinoic acid

The secretion of alpha 1-microglobulin by primary cultures of rat hepatocytes was found to increase upon the addition of interleukin-6 or leukemia inhibitory factor, two mediators of acute phase response. This stimulatory effect was further enhanced by dexamethasone. alpha 1-Microglobulin is synthesized as a precursor also containing bikunin, and the precursor protein is cleaved shortly before secretion. Our results therefore suggest that both alpha 1-microglobulin and bikunin are acute phase reactants in rat hepatocytes. Furthermore, we found that retinoic acid, previously shown to be involved in the regulation of cell differentiation and development, also stimulated alpha 1-microglobulin synthesis. Only free, uncomplexed alpha 1-microglobulin (28,000 Da) was detected in the hepatocyte media, suggesting that the complex between alpha 1-microglobulin and alpha 1-inhibitor 3, found in rat serum, is formed outside the hepatocyte.