• Fallon, Robert, (PI)

Project: Research project

Project Details


Receptors on liver cells play a fundamental role in normal liver growth
and development, and function as targets for selective delivery of cDNA
to hepatocytes (gene therapy). Their expression is tightly regulated;
however, relatively little is known about the mechanisms responsible. To
address these questions we propose to use as a model system the
asialoglycoprotein (ASGP) receptor of hepatocytes which is expressed on
the liver-derived cell line HepG2. It has been studied as a model of
receptor-mediated endocytosis, a process which delivers to the cell
nutrients, growth factors, pathogenic viruses and other proteins. In
previous studies we identified a novel regulatory mechanism of receptor
endocytosis: tyrosine kinase activation during the initial phase of
receptor clustering and internalization by the cell. The proposed project
will extend these findings to investigate several major questions. First,
the role of tyrosine kinase activation in receptor endocytosis will be
examined using intact and semi-intact cells. The cells used will be both
liver-derived cells and other cell lines transfected with wild-type ASGP
receptor cDNA and cDNA modified by site-directed mutagenesis. The semi-
intact cells permit access of macromolecular probes such as antibodies
to critical structural determinants of the receptor and the endocytic
machinery. Second, the identity and regulation of cellular kinases which
modulate receptor trafficking will be examined. Recently, we have
identified a protein tyrosine kinase that is tightly associated with the
ASGP receptor in a human hepatoma-derived cell line. This association is
regulated in turn by a cellular GTP-binding protein. Studies to be
performed include the characterization and identification of this
tyrosine kinase, and the structural analysis of receptor-kinase
interaction. Third, to investigate ASGP receptor function in normal liver
development, specimens of human liver tissue obtained from the
University of Minnesota and Nebraska Transplant Centers will be analyzed.
As complex formation between ASGP receptor and kinase may modulate
receptor function (described above), the abundance and activity of
receptor kinase complexes will be measured in normal liver and compared
to HepG2. The role of receptor-kinase association is completely unknown.
The goal of these studies is an understanding of both the basic cell
biology and the physiologic significance of this interaction.
Effective start/end date9/30/948/31/98


  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health: $152,087.00


  • Medicine(all)

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