Plasmin-induced smooth muscle cell proliferation requires epidermal growth factor activation through an extracellular pathway.
BACKGROUND
Plasminogen activators are used routinely for thrombolysis. They lead to the generation of the protease, plasmin, which can induce smooth muscle cell proliferation and may thus promote further intimal hyperplasia in the thrombolysed vessel. We have shown recently that plasmin induces extracellular signal-regulated kinase 1/2 (ERK1/2)-mediated cell proliferation. Plasmin can also activate metalloproteinases on the cell surface, which can release the tethered ligand heparin-binding epidermal growth factor (HB-EGF), which can in turn activate the epidermal growth factor receptor (EGFR).


METHODS
Murine aortic smooth muscle cells were cultured in vitro. Assays of DNA synthesis and cell proliferation, EGFR phosphorylation, and ERK1/2 activation were examined in response to plasmin in the presence and absence of the plasmin inhibitors (epsilon-aminocaproic acid and aprotinin), matrix metalloproteinase (MMP) inhibitor GM6001, HB-EGF inhibitor CRM197, HB-EGF inhibitory antibodies, EGF inhibitory antibodies, and the EGFR inhibitor AG1478.


RESULTS
Plasmin-induced smooth muscle cell DNA synthesis, which was blocked by EGFR and HB-EGF inhibition. Plasmin-induced time-dependent EGFR phosphorylation and ERK1/2 activation, which were inhibited by AG1478. This response was dependent on the proteolytic activity of plasmin since both plasmin inhibitors blocked the response. EGFR phosphorylation by plasmin was blocked by inhibition of MMP activity and the ligand HB-EGF. EGFR phosphorylation by EGF was not interrupted by inhibition of plasmin, MMPs, or HB-EGF. Direct blockade of the EGFR prevented activation by both plasmin and EGF.


CONCLUSIONS
Plasmin can induce smooth muscle cell proliferation through activation of EGFR by an extracellular MMP-mediated, HB-EGF-dependent process.
Roztocil
Elisa
E
Vascular Biology and Therapeutics Program, Division of Vascular Surgery, Department of Surgery, and the Center for Cardiovascular Research, University of Rochester, NY 14642, USA.
Nicholl
Suzanne M
SM
Galaria
Irfan I
II
Davies
Mark G
MG
D000818:Animals; D001011:Aorta / Q000166:cytology; D002455:Cell Division / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D005341:Fibrinolysin / Q000494:pharmacology*; D005343:Fibrinolytic Agents / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009115:Muridae; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation
D005343:Fibrinolytic Agents; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005341:Fibrinolysin