IRF1 is a member of the interferon regulatory transcription factor (IRF) family. IRF1 serves as an activator of interferons alpha and beta transcription, and in mouse it has been shown to be required for double-stranded RNA induction of these genes. IRF1 also functions as a transcription activator of genes induced by interferons alpha, beta, and gamma. Further, IRF1 has been shown to play roles in regulating apoptosis and tumor-suppression.IRF1 is highly regulated in human vascular lesions and exhibits a growth inhibitory function in coronary artery smooth muscle cells. Irf1-deficient mice displayed a high grade of susceptibility toward neointima formation following vessel injury. IRF1 led to G1 cell cycle arrest in coronary artery smooth muscle cells and induced the CDK inhibitor p21 (CDKN1A).