Characterization and biologic activities of recombinant rat soluble interleukin-6 receptor.
The soluble interleukin-6 receptor (sIL-6R) consists of the extracellular domain of the membrane-bound IL-6 receptor (gp80) found on many types of cells. Contrary to most other soluble cytokine receptors, it possesses in vitro agonistic properties, yet its physiologic role remains unknown. We have generated a cDNA encoding the rat sIL-6R and have expressed and purified the protein using Escherichia coli and baculovirus systems. Analysis of purified protein by electrophoresis and silver staining showed a single band migrating at 35 kDa for E. coli (nonglycosylated) and at 47 kDa for baculovirus-derived material. The purified protein is biologically active, as determined by the ability to convert human hepatoma cells (HepG2) from nonresponsive to responsive to rat IL-6 and induce acute-phase protein synthesis. Most important, we show that rat sIL-6R directly induces proliferation of the IL-6-dependent murine hybridoma cell line (B9) in an IL-6-like manner, with 50% proliferation induced by 100 ng/ml of baculovirus-derived receptor protein. Physiologic concentrations of sIL-6R dramatically enhance the sensitivity of B9 cells to IL-6, indicating that the bioassay for IL-6 is susceptible to modulation by the presence of sIL-6R in rodent serum samples. This sIL-6R-dependent B9 cell proliferation is fully abrogated by antibodies directed against rodent IL-6 and indicates autocrine production of low amounts of IL-6 by the B9 cell line.
Thibault
V
V
Department of Pathology, McMaster University, Hamilton, Canada.
Terlain
B
B
Gauldie
J
J
D000209:Acute-Phase Proteins / Q000096:biosynthesis*; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis / Q000235:genetics*; D016367:Baculoviridae; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002455:Cell Division / Q000502:physiology; D004926:Escherichia coli; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D051379:Mice; D051381:Rats; D018123:Receptors, Interleukin / Q000096:biosynthesis / Q000235:genetics*; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins / Q000096:biosynthesis*; D012995:Solubility; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D000209:Acute-Phase Proteins; D015703:Antigens, CD; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins