Increased expression of the insulin-like growth factor 1 receptor (IGF-1R) is associated with proliferation and survival of vascular smooth muscle cells (VSMCs). In cultured VSMCs, we reported that Angiotensin II (Ang II) increases transcription and expression of IGF-1R. Now, we show that mesenteric arteries of rats infused with Ang II develop thickening and increased IGF-1R expression. To determine how Ang II transcriptionally regulates IGF-1R expression in VSMCs, we generated 5'-end deletions of the IGF-1R promoter and measured Ang II-induced promoter-luciferase activity in VSMCs. Activities from these promoter sequences suggested that the Ang II-responsive region is located between -270 to -135 of the IGF-1R promoter. Using a DNase I foot printing analysis we identified two putative "NF-B-like" sequences located in the same region of the IGF-1R promoter. When we mutated either of these NF-B-like sites, Ang II-induced IGF-1R promoter activity decreased sharply. Electrophoretic mobility gel shift, anti p50 of NF-B supershift and chromatin immunoprecipitation assays demonstrated that both the p65 and p50 subunits of NF-B will bind to this Ang II-response element in the IGF-1R promoter. When we blocked the Ras/MEK1 pathway or the IKK pathway, both Ang II-induced IGF-1R promoter activity and expression of IGF-1R protein significantly declined. Our results indicate that the mechanism by which Ang II stimulates IGF-1R expression in VSMCs involves NF-B binding to NF-B sites in the IGF-1R promoter, leading to expression of IGF-1R through both Ras/MEK1-and IKK-dependent pathways. Since IGF-1R is a major factor associated with thickening of mesenteric vessels, our results provide potential therapeutic targets.