Objective: Id2 (inhibitor of DNA-binding 2), a member of the helix-loop-helix family of transcription regulators, plays important roles in cell proliferation and differentiation. Recent reports have documented that Id2 is up-regulated during vascular lesion formation and overexpression of Id2 promotes vascular smooth muscle cell (VSMC) proliferation. However, the transcriptional regulation of Id2 gene expression in VSMC remains unexplored.
Methods and results: Using Northern- and Western-blot analyses, we documented that interleukin-1beta (IL-1beta) induced Id2 gene expression in VSMC in a time- and dose-dependent manner. Overexpression of early growth response-1 (Egr-1) in VSMC induced Id2 expression while IL-1beta-induced Id2 expression was abrogated in VSMC by the Egr-1 repressor, NGFI-A binding protein 2 (NAB2), expressed from an adenovirus. Overexpression of Egr-1 transactivated the Id2 promoter in reporter assays dependent on the presence of intact putative Egr-1 binding sites as determined by mutagenesis. Finally, electrophoretic mobility shift assays (EMSA) demonstrated that the Egr-1 protein can bind the Egr-1 sites derived from the human Id2 promoter in vitro and chromatin immunoprecipitation identified the putative Egr-1 site between -723 to -712 as the functional Egr-1 binding site in vivo.
Conclusions: Our data demonstrate that IL-1beta-induced Id2 expression in VSMC is mediated by the transcription factor Egr-1 in VSMC.