EMMPRIN mediates beta-adrenergic receptor-stimulated matrix metalloproteinase activity in cardiac myocytes.

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.

RNA helicase A interacts with dsDNA and topoisomerase IIalpha.

RNA helicase A (RHA) is a multifunctional protein involved in various nuclear processes such as transcription and RNA export. It is believed that the interacting factors play important roles in determining the functional specificity of RHA. Here we show that RHA directly interacts with double-stranded (ds) nucleic acids (NAs) and assembles complexes with topoisomerase IIalpha. First, electrophoresis mobility shift assays demonstrate that RHA interacts with dsDNAs of different lengths ranging from 15 to 104 bp. Secondly, the binding of RHA to closed circular dsDNA stimulates the relaxation reaction catalyzed by either calf thymus topoisomerase I or HeLa topoisomerase IIalpha. Thirdly, immunoprecipitation, coupled with western blot analysis using anti-RHA and anti-topoisomerase IIalpha antibodies, shows that RHA and topoisomerase IIalpha assemble a complex in the presence of as yet unknown RNA molecules and additional protein factors such as Ubc9. Our observation suggests physical and functional interaction between RHA and topoisomerase IIalpha, which, perhaps, play important roles in regulating chromatin structure. The putative role of RHA-topoisomerase IIalpha complex in RNA polymerase II-mediated transcription is discussed.