Objection-Thrombin upregulates expression of several proteins in vascular smooth muscle cells (VSMCs) which may contribute to atherosclerosis. Here, we investigated the mechanisms underlying thrombin-induced EGF receptor (EGFR) expression and its effect on VSMCs. Methods and Results-Normal rat VSMCs were used. First, Western blotting and RT-PCR analyses showed that thrombin induces the expression of EGFR at transcription and translation levels in VSMCs. Second, pharmacological inhibitors,

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... nt negative mutants, and short hairpin RNA interference (shRNA) technology enabled us to demonstrate that thrombin-induced EGFR expression is mediated through PKC(␦)/c-Src-dependent transactivation of EGFR linking to PI3K/Akt and ERK1/2. We further investigated whether the transcription factors AP-1 and NF-B are involved in this response by a promoter assay. Finally, data obtained by using EGFR shRNA technology and XTT assay demonstrated that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR. Conclusions-Our results demonstrate that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR via a PKC(␦)/c-Src-dependent transactivation of EGFR, PI3K-Akt, and ERK, and AP-1/NF-B pathway. (Arterioscler Thromb Vasc Biol. 2009;29:1594-1601.)