Biosynthesis of lipopolysaccharide-binding protein in rabbit hepatocytes.
Studies reported here show that the recently discovered acute-phase protein, lipopolysaccharide-binding protein (LBP), is synthesized by hepatocytes. For these studies, explanted rabbit hepatocytes were grown in the presence of 35S-methionine. Biosynthetically labelled LBP in the cells and supernatant was identified using immunoprecipitation with rat anti-rabbit LBP antibody. This antibody immunoprecipitates both the LBP polypeptide and the glycosylated protein. With a cell-free translation system a comparison of RNA from normal rabbit liver with that isolated from acute-phase rabbit liver indicated that a translatable LBP message is only found in the RNA from acute-phase liver. Studies with explanted rabbit hepatocytes showed that several forms of LBP distinguishable by migration in SDS-PAGE are secreted into the extracellular medium. This heterogeneity probably is a result of differences in glycosylation of LBP since pretreatment of the hepatocytes with tunicamycin results in accumulation of a single polypeptide with an apparent mass of 50 kD in SDS-PAGE. Explanted rabbit hepatocytes spontaneously synthesize and secrete LBP and express LBP mRNA as detected by cell-free translation; thus, it was not possible to upregulate the expression of LBP. Nevertheless, these studies form the basis for future investigations on the regulation of LBP biosynthesis.
Klinikum der Johannes-Gutenberg-Universität, I. Medizinische Klinik und Poliklinik, Mainz, FRG.
G
G
Ramadori
K H
KH
Meyer zum Buschenfelde
P S
PS
Tobias
J C
JC
Mathison
R J
RJ
Ulevitch
D000209:Acute-Phase Proteins / Q000096:biosynthesis*; D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis*; D002478:Cells, Cultured; D015870:Gene Expression; D006023:Glycoproteins / Q000096:biosynthesis; D008099:Liver / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008970:Molecular Weight; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D014415:Tunicamycin / Q000494:pharmacology; D000099231:Lipopolysaccharide-Binding Protein
D000209:Acute-Phase Proteins; D002352:Carrier Proteins; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D014415:Tunicamycin; D000099231:Lipopolysaccharide-Binding Protein