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Department of Medical Specialties, The University of Texas Health Center at Tyler, Tyler, Texas 75708
The urokinase-type
plasminogen activator (uPA) interacts with its receptor (uPAR) to
promote local proteolysis as well as cellular proliferation and
migration. These functions contribute to the pathogenesis of lung
inflammation and remodeling as well as the growth and invasiveness of
lung neoplasms. In this study, we sought to determine if uPA alters its
own expression in lung epithelial cells. Using immunoprecipitation and
Western and Northern blotting techniques, we found that uPA treatment
enhanced uPA expression in Beas2B lung epithelial cells in a time- and
concentration-dependent manner. The induction of uPA expression is
mediated through its cell surface receptor uPAR and does not require
uPA enzymatic activity. The amino-terminal fragment of uPA, lacking the
catalytic domain, is sufficient to induce uPA expression. The serine
protease plasmin and the protease inhibitor aprotinin failed to alter
uPA-mediated uPA expression, whereas
-thrombin potentiated the
response. Pretreatment of Beas2B cells with a tyrosine kinase
inhibitor, herbimycin, suggests that activation of tyrosine kinase(s)
is involved in the uPA-mediated uPA expression. Induction of uPA
expression by exposure of lung-derived epithelial cells to uPA is a
newly defined pathway by which this protease could influence expression
of local fibrinolytic activity and other uPA-dependent cellular
responses germane to lung inflammation or neoplasia.
urokinase; urokinase receptor; plasminogen activator inhibitor;
-thrombin; phosphorylation
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