Cell-free-synthesized interleukin-6 (BSF-2/IFN-beta 2) exhibits hepatocyte-stimulating activity.
Secretory products of cultured human blood monocytes contain a hepatocyte-stimulating factor which is able to induce the acute-phase proteins alpha 2-macroglobulin and fibrinogen in rat liver cells. Total RNA was isolated from unstimulated and lipopolysaccharide-stimulated human monocytes and translated in a reticulocyte lysate. The capability of the cell-free synthesized proteins to induce the acute-phase proteins alpha 2-macroglobulin and fibrinogen was assayed in rat hepatocyte primary cultures and in the rat hepatoma cell line Fao. The products translated from the mRNA of lipopolysaccharide-stimulated human monocytes induced mRNAs for alpha 2-macroglobulin and fibrinogen and therefore contain hepatocyte-stimulating factor. The translation products of unstimulated monocytes had no effect. A cDNA containing the coding sequence for interleukin-6 (B-cell stimulatory factor 2, interferon-beta 2/26-kDa protein, interleukin HP1) derived from human T-cells cloned into the transcription vector pGEM4 was transcribed in vitro. Translation of the isolated RNA in a reticulocyte lysate led to the synthesis of a protein of about 25 kDa. This cell-free synthesized interleukin-6 exhibited hepatocyte-stimulating activity measured by the induction of beta-fibrinogen mRNA in Fao cells. Using an antibody against interleukin-6, two proteins of 22 kDa and 23 kDa were immunoprecipitated from the culture medium of lipopolysaccharide-stimulated human monocytes. These two proteins were not synthesized by unstimulated monocytes. When total RNA from unstimulated human monocytes and lipopolysaccharide-stimulated human monocytes and lymphocytes was subjected to Northern analysis and hybridized with the interleukin-6 cDNA, a strong hybridization signal corresponding to an RNA of about 1300 bases was detected only in the RNA from lipopolysaccharide-stimulated human monocytes, indicating that human monocytes express the interleukin-6 gene after stimulation. The data presented in this paper strongly suggest that hepatocyte-stimulating factor from human monocytes and interleukin-6 from T-cells are identical.
Geiger
T
T
Biochemisches Institut, Freiburg, Federal Republic of Germany.
Andus
T
T
Bauer
J
J
Northoff
H
H
Ganter
U
U
Hirano
T
T
Kishimoto
T
T
Heinrich
P C
PC
D000818:Animals; D002460:Cell Line; D002474:Cell-Free System; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000096:biosynthesis; D006801:Humans; D015850:Interleukin-6; D007378:Interleukins / Q000096:biosynthesis / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008099:Liver / Q000187:drug effects*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism; D008970:Molecular Weight; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D012313:RNA / Q000032:analysis; D051381:Rats; D000511:alpha-Macroglobulins / Q000096:biosynthesis
D015850:Interleukin-6; D007378:Interleukins; D008070:Lipopolysaccharides; D000511:alpha-Macroglobulins; D012313:RNA; D005340:Fibrinogen