Stimulation of human smooth muscle cell proliferation by thrombin involves increased synthesis of platelet-derived growth factor.
OBJECTIVE
Thrombin generated at sites of vascular injury not only participates in the coagulation cascade but can also signal other events related to cell mitogenesis and migration. In this report, we investigated the effects of thrombin on the proliferation of human arterial smooth muscle cells (SMCs) in culture and its interaction with platelet-derived growth factor (PDGF).


METHODS
Human arterial SMCs originated from a renal artery were grown in cell culture. The effect of thrombin on DNA synthesis was evaluated by 3H-thymidine incorporation. The effect of thrombin on inositol-phosphate formation by SMCs was also analyzed as well as the binding of PDGF AA and BB to these cells. PDGF secretion was analyzed by radioimmunoassay (RIA).


RESULTS
Exposure of cultured human SMCs to thrombin caused an increased rate of DNA synthesis in a dose-response manner, with a maximal stimulatory effect at a concentration of 2.0 U/mL. Thrombin was found to increase the accumulation of inositol phosphates and to increase the production of PDGF as measured by RIA. Exposure of cells to 2.0 U/mL thrombin resulted in a strong decrease in PDGF AA binding to PDGF receptors and did not change PDGF BB binding, probably indicating that PDGF alpha-receptors could be occupied by endogenously produced PDGF A.


CONCLUSIONS
Thrombin stimulates human vascular SMC proliferation in a dose-response way, in part by the formation of inositol phosphates. The mechanism responsible for this effect involves, at least in part, an increased endogenous synthesis of PDGF.
Department of Hematology, University of São Paulo Medical School, SP, Brazil.
S P
SP
Bydlowski
M M
MM
Pares
R P
RP
Soares
A A
AA
Lopes
D000925:Anticoagulants / Q000378:metabolism; D000077214:Becaplermin; D001777:Blood Coagulation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D003029:Coagulants / Q000008:administration & dosage / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007295:Inositol Phosphates / Q000096:biosynthesis; D008934:Mitogens / Q000008:administration & dosage / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010982:Platelet-Derived Growth Factor / Q000096:biosynthesis* / Q000378:metabolism; D011485:Protein Binding; D020574:Proto-Oncogene Proteins c-sis; D019275:Radiopharmaceuticals; D017479:Receptors, Platelet-Derived Growth Factor / Q000187:drug effects / Q000378:metabolism; D012077:Renal Artery / Q000166:cytology; D013268:Stimulation, Chemical; D013917:Thrombin / Q000008:administration & dosage / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism; D014316:Tritium
D000925:Anticoagulants; D003029:Coagulants; D007295:Inositol Phosphates; D008934:Mitogens; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D019275:Radiopharmaceuticals; C075278:platelet-derived growth factor A; D014316:Tritium; D000077214:Becaplermin; D004247:DNA; D017479:Receptors, Platelet-Derived Growth Factor; D013917:Thrombin; D013936:Thymidine