Regulation of synthesis and secretion of major rat acute‐phase proteins by recombinant human interleukin‐6 (BSF‐2/1L‐6) in hepatocyte primary cultures

Abstract

The regulation of the three major acute-phase proteins a,-macroglobulin, cysteine proteinase inhibitor and a,-antitrypsin by recombinant human interleukin-1 fi, recombinant human interleukin-6 and recombinant human tumor necrosis factor a was studied in rat hepatocyte primary cultures. Synthesis and secretion of the acute-phase proteins was measured after labeling with [3sS]methionine and immunoprecipitation.Incubation of hepatocytes with interleukin-6 led to dose-dependent and time-dependent changes in the synthesis of the three major acute-phase proteins and albumin, similar to those occurring in vivo during experimental inflammation. a2-Macroglobulin and cysteine proteinase inhibitor synthesis was induced 54-fold and %fold, respectively, 24 h after the addition of 100 units/ml interleukin-6. At the same time synthesis of the negative acute-phase protein albumin was reduced to 30% of controls. Half-maximal effects were achieved with 4 units interleukin-6/ml. Interleukin-1fi had only a partial effect on the regulation of the four proteins studied: only a twofold stimulation of a,-macroglobulin and a 60% reduction of albumin synthesis were observed. Tumor necrosis factor a did not alter the synthesis of acute-phase proteins.The stimulation of a2-macroglobulin and cysteine proteinase inhibitor synthesis by interleukin-6 was inhibited by interleukin-1 p in a dose-dependent manner.In pulse-chase experiments the effect of interleukin-lfi, interleukin-6 and tumor necrosis factor CI on the secretion of acute-phase proteins was examined. Interleukin-6 markedly accelerated the secretion of total proteins and a,-macroglobulin, whereas the secretion of cysteine proteinase inhibitor, a,-antitrypsin and albumin was not affected. The inhibition of N-glycosylation by tunicamycin abolished the effect of interleukin-6 on the secretion of a2-macroglobulin, indicating a possible role of interleukin-6 on N-glycosylation.Bacterial or parasitic infections, physical and chemical traumata, malignant tumors and immunologic disorders lead to a series of local and systemic reactions of the organism, the so-called acute-phase response [l, 21. The local reaction includes the dilation of blood vessels, alteration in blood flow and clotting, immigration of neutrophils and macrophages, release of lysosomal proteases and the formation of inflammatory mediators. These mediators cause a systemic reaction characterized by fever and pain, leukocytosis, decrease in plasma iron and zinc levels and increased synthesis of acutephase proteins (reviewed in [l, 21). Many of the acute-phase proteins are proteinase inhibitors involved in the protection of healthy tissue from proteinases such as elastase, collagenase and cathepsin G released from granulocytes and macrophagesIn the rat the proteinase inhibitors a,-macroglobulin (azM), cysteine proteinase inhibitor and al-antitrypsin (a,AT) represent positive acute-phase reactants. During acute inflammation their serum levels increase about 100-fold, 8-fold, and 2-fold respectively 14-61. The increase in seru...

The synthesis of human α‐2‐HS glycoprotein is down‐regulated by cytokines in hepatoma HepG2 cells

“…In agreement with our observations, Andus et al [23] have described an additive down-regulation of albumin synthesis in rat hepatocyte primary cultures using a combination of rhlL6 and rhlLl~. In our experiments, rhlL6 appears to be the major inducer of the decrease of AHSG synthesis in vitro.…”

Biologically active products of stimulated liver macrophages (Kupffer cells)

“…As an example the various influences between liver macrophages and hepatocytes may be mentioned. IL-6 that is produced upon exposure to inflammatory substances (LPS, viruses) by the Kupffer cells in the neighbourhood of the parenchymal cells elicits the production of the anti-inflammatory acutephase proteins [156]. At the same time, thromboxane and PGE2 triggered by the same stimuli increase the rate of glycogenolysis thereby supplying the hepatocytes and other cells with the energy-providing substrate, glucose.…”

“…IL-6 is the most potent stimulator known for the elicitation of acute-phase protein synthesis in hepatocytes [156]. Little mRNA for this receptor is found in quiescent parenchymal cells; however, after exposure to glucocorticoid hormones, its intracellular level is greatly enhanced.…”

A new hepatocyte stimulating factor: cardiotrophin‐1 (CT‐1)

“…For comparison, cells were incubated with LIF, OSM, and IL-6, which are well-documented hepatocytestimulating factors [2][3][4]24,25]. Fig.…”