Thrombin-induced p38 mitogen-activated protein kinase activation is mediated by epidermal growth factor receptor transactivation pathway

1 Thrombin is a potent mitogen for vascular smooth muscle cells (VSMC) and has been implicated its pathogenic role in vascular remodelling However, th e signalling pathways by which thrombin mediates its mitogenic response are not fully understood. 2 We have previously reported that thrombin activates p38 mitogen-activated protein kinase (p38 MAPK) by a tyrosine kinase-dependent mechanism, and th at p38 MAPK has a role in thrombin-induced mitogenic response in rat VSMC. 3 In the present study, we examine the involvement of epidermal growth fact or (EGF) receptor in thrombin-induced p38 MAPK activation. We found that th rombin induced EGF receptor tyrosine phosphorylation (transactivation) in A 10 cells, a clonal VSMC cell line. A selective inhibitor of EGF receptor ki nase (AG1478) inhibited the p38 MAPK activation in a dose-dependent manner, whereas it had no effect on the response to platelet-derived growth factor (PDGF). EGF receptor phosphorylation induced by thrombin was inhibited by BAPTA-AM and GF109203X, which suggest a requirement for intracellular Ca2increase and protein kinase C. 4 We next examined the effect of AG1478 on thrombin-induced DNA synthesis. AG1478 inhibited thrombin-induced DNA. synthesis in a dose-dependent manner . In contrast, PDGF-induced DNA synthesis was not affected by AG1478. 5 In conclusion, these data suggest that the EGF receptor transactivation a nd subsequent p38 MAPK activation is required for thrombin-induced prolifer ation of VSMC.