SYNTHESIS AND SECRETION OF MULTIPLE FORMS OF BETA-2-INTERFERON B-CELL DIFFERENTIATION FACTOR-II HEPATOCYTE-STIMULATING FACTOR BY HUMAN-FIBROBLASTS AND MONOCYTES

Abstract

The cDNA for human .beta.2-interferon (IFN-.beta.2)/B-cell differentiation factor 2/hepatocyte-stimulating factor was expressed in Escherichia coli to yield a fusion protein which contains the 182 carboxyl-terminal amino acids of IFN-.beta.2 fused to a 34-amino acid prokaryotic leader peptide (rIFN-.beta.2). When added to cultures of human hepatoma cell line Hep3B2, rIFN-.beta.2 as well as preparations of natural IFN-.beta.2 enhanced secretion of positive acute phase reactants such as .alpha.1-antichymotrypsin, complement C3, fibrinogen, and .alpha.1-acid glycoprotein and inhibit secretion of albumin, confirming that a protein derived from the IFN-.beta.2 gene can have hepatocyte-stimulating factor activity. We have prepared a rabbit polyclonal antiserum to the E. coli-derived human IFN-.beta.2 fusion protein. This polyclonal antiserum inhibits the hepatocyte-stimulating and B-cell differentiation activities of appropriate IFN-.beta.2 preparations. The anti-rIFN-.beta.2 antiserum has been used in immunoprecipitation experiments and in Western blots to help define the secretory proteins derived from the IFN-.beta.2 gene in fibroblasts and monocytes. "Uninduced" human FS-4 fibroblasts as well as those induced with interleukin-1.alpha., tumor necrosis factor, or bacterial lipopolysaccharide secrete at least five forms of IFN-.beta.2 of apparent molecular mass in the range from 23 to 30 kDa which can be resolved by polyacrylamide gel electrophoresis under denaturing and reducing conditions. The three higher molecular mass forms are not observed when FS-4 cells are induced in the presence of tunicamycin, suggesting that these forms are N-glycosylated (gp28, gp29, and gp30). Although secretion of the two lower molecular mass forms is resistant to tunicamycin, they are labeled by [3H]glucosamine (gp23-gp25). The inclusion of cycloheximide during the [35S]methionine labeling of induced FS-4 cells results in the preferential synthesis and secretion of the 29-kDa triplet. Human monocytes induced with bacterial lipopolysaccharide also secrete several distinct forms of IFN-.beta.2 in the size range from 23 to 30 kDa which co-migrate in polyacrylamide gels with those obtained from FS-4 cells. Our observations help relate previous description of multiple forms of hepatocyte-stimulating factor to specific proteins derived from the IFN-.beta.2 gene.