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Infection and Immunity, November 1998, p. 5089-5098, Vol. 66, No. 11
Department of Surgery1
and
Department of Cell Biology and
Physiology,3 University of Pittsburgh School of
Medicine, Pittsburgh, Pennsylvania 15261, and
Division of
Molecular Medicine, Department of Medicine, North Shore University
Hospital-New York University, Manhasset, New York
110302
Received 15 October 1997/Returned for modification 5 December
1997/Accepted 6 August 1998
Studies were undertaken to examine hepatocyte CD14 expression
during endotoxemia. Our results show that lipopolysaccharide (LPS)
treatment in vivo caused a marked upregulation in CD14 mRNA and protein
levels in rat hepatocytes. Detectable increases in mRNA were seen as
early as 1.5 h after LPS treatment; these increases peaked at
20-fold by 3 h and returned to baseline levels by 24 h. In
situ hybridization localized the CD14 mRNA expression to hepatocytes
both in vitro and in vivo. Increases in hepatic CD14 protein levels
were detectable by 3 h and peaked at 12 h. Hepatocytes from
LPS-treated animals expressed greater amounts of cell-associated CD14
protein, and more of the soluble CD14 was released by hepatocytes from
LPS-treated rats in vitro. The increases in hepatocyte CD14 expression
during endotoxemia occurred in parallel to increases of CD14 levels in
plasma. To provide molecular identification of the hepatocyte CD14, we
cloned the rat liver CD14 cDNA. The longest clone consists of a
1,591-bp insert containing a 1,116-bp open reading frame. The deduced
amino acid sequence is 372 amino acids long, has 81.8 and 62.8%
homology to the amino acid sequences of mouse and human CD14,
respectively, and is identical to the rat macrophage CD14. The
expressed CD14 protein from this clone was functional, as indicated by
NF-
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Expression of CD14 by Hepatocytes: Upregulation by
Cytokines during Endotoxemia
B activation in response to LPS and fluorescein
isothiocyanate-LPS binding in CHO cells stably transfected with rat
CD14. A nuclear run-on assay showed that CD14 transcription rates were
significantly increased in hepatocytes from LPS-treated animals,
indicating that the upregulation in CD14 mRNA levels observed in rat
hepatocytes after LPS treatment is dependent, in part, on increased
transcription. In vitro and in vivo experiments indicated that
interleukin-1
and/or tumor necrosis factor
participate in the
upregulation of CD14 mRNA levels in hepatocytes. Our data indicate that
hepatocytes express CD14 and that hepatocyte CD14 mRNA and protein
levels increase rapidly during endotoxemia. Our observations also
support the idea that soluble CD14 is an acute-phase protein and that
hepatocytes could be a source for soluble CD14 production.
*
Corresponding author. Mailing address: Department of
Surgery, University of Pittsburgh, W1504 BST, Lothrop and Terrace Sts., Pittsburgh, PA 15261. Phone: (412) 624-6740. Fax: (412) 624-1172. E-mail: shubing{at}pitt.edu.
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