Abstract —Both the processes of atherosclerosis and plaque rupture are indicated to be influenced by matrix metalloproteinase (MMP) activity. We therefore searched for common functional variation in the matrix metalloelastase (MMP-12) gene locus that may be implicated in coronary artery disease. Single-strand conformation polymorphism analysis of DNA from healthy individuals detected a common polymorphism within the MMP-12 gene promoter (an A-to-G substitution at position –82). The frequency of the G allele was 0.19. The polymorphism influences the binding of the transcription factor activator protein-1 (AP-1) in electromobility shift assay. A higher binding affinity of AP-1 to the A allele was associated with higher MMP-12 promoter activity in vitro in transient transfection studies in U937 and murine lung macrophage (MALU) cells. Phorbol 12-myristate 13-acetate (PMA) and insulin, 2 known activators of AP-1, increased the binding of AP-1 to the MMP-12 promoter, with higher affinity for the A allele. In transfection experiments, both the A and the G alleles responded to insulin and PMA, the A allele showing higher promoter activity than the G allele. Furthermore, Western blot analysis demonstrated that insulin increased MMP-12 protein production. To analyze whether the –82 A/G polymorphism is associated with coronary artery disease, 367 consecutive patients who underwent percutaneous transluminal coronary angiography with stent implantation were genotyped. In patients (n=71) with diabetes, the A allele was associated with a smaller luminal diameter. In conclusion, a common functional polymorphism within the MMP-12 promoter influences coronary artery luminal dimensions in diabetic patients with manifest coronary artery disease.