The Stem Loop II within the 5′ Nontranslated Region of Clinical Coxsackievirus B3 Genomes Determines Cardiovirulence Phenotype in a Murine Model

Coxsackievirus B3 (CVB3) is a principal viral cause of acute myocarditis in humans and has been implicated in the pathogenesis of dilated cardiomyopathy. It has been demonstrated elsewhere that, for 2 wild-type CVB3 strains, the primary molecular determinant of cardiovirulence phenotype localizes to the 5' nontranslated region (5' NTR). Here in this study, through construction of CVB3 chimeras, the predicted stem loop (SL) II within the 5' NTR has been identified as a primary viral determinant of cardiovirulence. Replication assays in cardiac-derived murine fibroblasts revealed that only cardiovirulent strains grow robustly at 37°C, whereas all virus strains replicate efficiently in HeLa cells. Computational analyses of RNA secondary structure suggest that the predicted SLII of the noncardiovirulent isolate differs significantly from that of myocarditic strains. These results indicate that, for clinical CVB3 isolates, the major determinant of cardiovirulence localizes to the predicted SLII. The identity of this higher-order RNA structure may be essential for productive infection of cardiac cells.