Plasmin induces smooth muscle cell proliferation.
BACKGROUND
Plasminogen activators are routinely used 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. The signaling pathways used by plasmin are not understood.


METHODS
Murine aortic smooth muscle cells were cultured in vitro. Assays of DNA synthesis, cell proliferation, MAPKK and MAPK activation were examined in response to plasmin alone and in the presence of plasmin inhibitors (epsilon-aminocaproic acid and aprotinin), pertussis toxin (Galphai inhibitor, PTx), GP-2A (Galphaq inhibitor), wortmannin (PI3-K inhibitor, Wn), LY294002, (PI3-K inhibitor, LY), PD98059 (MEK inhibitor, PD), and SB203580 (p38MAPK inhibitor, SB).


RESULTS
Plasmin produced concentration dependent smooth muscle cells DNA synthesis and proliferation and induced ERK1/2 and p38MAPK phosphorylation. Inhibition of the proteolytic activity of plasmin prevented these responses. The ERK1/2 inhibitor, PD, but not the p38MAPK inhibitors, SB, blocked cell proliferation. The activation of the MEK1/2 and ERK1/2 pathway was both Galphai dependent (PTx-sensitive) and Galphaq dependent (GP-2A-sensitive). It was blocked by the PI3-K inhibitors, Wn and LY. PI3-K activation as measured by akt phosphorylation was dependent on Galphai, but was independent of Galphaq.


CONCLUSIONS
Plasmin induces smooth muscle cell proliferation. Plasmin induced ERK1/2 phosphorylation occurs through two pathways: one which is Galphai mediated/PI3-K dependent and a second which is Galphaq mediated/PI3K independent. p38MAPK appears not to be involved in plasmin-mediated cell proliferation. This pattern of activation is distinct from that seen with urokinase plasminogen activator.
Nicholl
Suzanne M
SM
Division of Vascular Surgery, Department of Surgery, Center for Cardiovascular Research, University of Rochester, Rochester, New York 14642, USA.
Roztocil
Elisa
E
Galaria
Irfan I
II
Davies
Mark G
MG
D000818:Animals; D007611:Aprotinin / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects*; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects; D004789:Enzyme Activation; D005341:Fibrinolysin / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology* / Q000187:drug effects; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt
D011518:Proto-Oncogene Proteins; D007611:Aprotinin; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D005341:Fibrinolysin