Extracellular matrix metalloproteinase inducer (EMMPRIN) expression is increased in myocardium from patients with dilated cardiomyopathy and animal models of heart failure. However, little is known about the regulated expression or functional role of EMMPRIN in the myocardium. In rat cardiac cells, EMMPRIN is expressed on myocytes but not endothelial cells or fibroblasts. Therefore, we tested the hypothesis that EMMPRIN expression regulates matrix metalloproteinase (MMP) activity in rat ventricular myocytes in vitro. In adult rat ventricular myocytes (ARVM), beta-adrenergic receptor (betaAR) stimulation and H(2)O(2) (24 h) each increased EMMPRIN expression as assessed by immunoblotting. Pretreatment with a catalase/superoxide dismutase mimetic or adenoviral-mediated expression of catalase or a dominant-negative c-jun N-terminal kinase-1 (JNK) mutant inhibited the betaAR- and H(2)O(2)-stimulated increases in EMMPRIN expression suggesting that EMMPRIN expression is regulated via a reactive oxygen species-dependent JNK pathway. To determine whether EMMPRIN expression regulates matrix metalloproteinase (MMP) activity, EMMPRIN activity was inhibited by adenoviral expression of an inhibitory mutant of EMMPRIN. Expression of mutant EMMPRIN inhibited the betaAR-stimulated increases in MMP2 expression and zymographic MMP activity. Thus, in cardiac myocytes betaAR stimulation induces the expression of EMMPRIN via the ROS-dependent activation of JNK. The resulting increase in EMMPRIN activity stimulates MMP expression and activity. These findings suggest that in the myocardium the regulated expression of EMMPRIN is a determinant of MMP activity and may thus play a role in myocardial remodeling.