Lipopolysaccharide binding protein expression in primary human hepatocytes and HepG2 hepatoma cells.
Lipopolysaccharide (LPS)-binding protein (LBP) is a normal plasma protein and an acute phase reactant important for host responses to Gram-negative bacteria and LPS. LBP forms high affinity complexes with LPS which bind to CD14, a monocyte surface protein, to initiate the release of inflammatory mediators. We found that human primary hepatocytes synthesize LBP and that the synthesis is up-regulated by interleukin (IL)-6. To examine this phenomenon in more detail, we evaluated the capacity of IL-6, IL-1, and tumor necrosis factor to induce LBP synthesis in HepG2 cells in the presence or absence of dexamethasone. IL-6 induced LBP synthesis. Dexamethasone, IL-1, and tumor necrosis factor had a synergistic effect when combined with IL-6, but demonstrated minimal effect independently. LBP biosynthesis was evaluated by immunoprecipitation of 35S-labeled LBP from HepG2 supernatants, measurement of steady-state LBP mRNA levels, and analysis of LBP-dependent LPS binding to CD14 positive cells. An 35S-labeled, 60-kDa protein was immunoprecipitated with anti-LBP antibody from IL-6-stimulated HepG2 cell supernatants. Northern blot analysis of cellular RNA revealed an increase in LBP mRNA in IL-6-stimulated cells. CD14 expressing cells bound fluoresceinated LPS in the presence of supernatants from HepG2 cells treated with IL-6. These data provide the first information about specific cytokine and dexamethasone regulation of LBP expression in HepG2 cells. LBP behaves like a Type 1 acute phase protein.
Grube
B J
BJ
Department of Immunology, Scripps Research Institute, La Jolla, California 92037.
Cochane
C G
CG
Ye
R D
RD
Green
C E
CE
McPhail
M E
ME
Ulevitch
R J
RJ
Tobias
P S
PS
D000209:Acute-Phase Proteins / Q000096:biosynthesis; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D002460:Cell Line; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology; D006090:Gram-Negative Bacteria; D006801:Humans; D015151:Immunoblotting; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism*; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D016207:Cytokines; D003907:Dexamethasone; D007375:Interleukin-1; D015850:Interleukin-6; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000099231:Lipopolysaccharide-Binding Protein