Thrombin increases expression of urokinase receptor by activation of the thrombin receptor.
OBJECTIVE
To investigate the effect of thrombin on the urokinase plasminogen activator receptor (u-PAR) in retinal pigment epithelial (RPE) cells.


METHODS
The authors analyzed u-PAR mRNA by Northern blot hybridization. Retinal pigment epithelial cell surface u-PAR was assayed by measuring the amount of functional urokinase plasminogen activator (u-PA) bound to cells at saturation. Retinal pigment epithelial cells were derived from fetal retinal tissue and established in primary cell culture.


RESULTS
Thrombin increased u-PAR mRNA 4-fold in RPE cells examined by Northern blot hybridization, whereas the amount of thrombin receptor mRNA was unchanged. Thrombin stimulated u-PA binding to RPE cells 2.5- to 5-fold in a time- and dose-dependent manner. Hirudin, a thrombin antagonist, completely blocked the effects of thrombin on u-PAR expression in RPE cells. Phosphatidylinositol phospholipase C treatment of RPE cells resulted in the abolition of thrombin-induced u-PA binding. Recombinant soluble u-PAR competitively inhibited two-chain u-PA binding to the surface of thrombin-treated RPE cells. A thrombin receptor agonist peptide (SFLLRNPNDKYEPF) also induced a 2.5-fold increase in binding of u-PA to the surface of RPE cells.


CONCLUSIONS
Thrombin increases u-PAR expression by RPE cells by a mechanism involving activation of the seven transmembrane thrombin receptor.
Yang
Z
Z
Cancer Research Institute, University of California at San Francisco 94143-0128, USA.
Cohen
R L
RL
Lui
G M
GM
Lawrence
D A
DA
Shuman
M A
MA
D000595:Amino Acid Sequence; D015152:Blotting, Northern; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010960:Plasminogen Activators / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000096:biosynthesis*; D018179:Receptors, Thrombin / Q000737:chemistry / Q000378:metabolism*; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins; D013917:Thrombin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000494:pharmacology; D014568:Urokinase-Type Plasminogen Activator / Q000096:biosynthesis
C524898:PLAUR protein, human; D010446:Peptide Fragments; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins; D010738:Type C Phospholipases; D010960:Plasminogen Activators; D013917:Thrombin; D014568:Urokinase-Type Plasminogen Activator