Structures and Functions of Viral 5' Non-Coding Genomic RNA Domain-I in Group-B Enterovirus Infections.

Group-B enteroviruses (EV-B) are ubiquitous naked single-stranded positive RNA viral pathogens that are responsible for common acute or persistent human infections. Their genome is composed in the 5' end by a non-coding region, which is crucial for the initiation of the viral replication and translation processes. RNA domain-I secondary structures can interact with viral or cellular proteins to form viral ribonucleoprotein (RNP) complexes regulating viral genomic replication, whereas RNA domains-II to -VII (internal ribosome entry site, IRES) are known to interact with cellular ribosomal subunits to initiate the viral translation process. Natural 5' terminally deleted viral forms lacking some genomic RNA domain-I secondary structures have been described in EV-B induced murine or human infections. Recent in vitro studies have evidenced that the loss of some viral RNP complexes in the RNA domain-I can modulate the viral replication and infectivity levels in EV-B infections. Moreover, the disruption of secondary structures of RNA domain-I could impair viral RNA sensing by RIG-I (Retinoic acid inducible gene I) or MDA5 (melanoma differentiation-associated protein 5) receptors, a way to overcome antiviral innate immune response. Overall, natural 5' terminally deleted viral genomes resulting in the loss of various structures in the RNA domain-I could be major key players of host-cell interactions driving the development of acute or persistent EV-B infections.

Enterovirus Persistence in Cardiac Cells of Patients With Idiopathic Dilated Cardiomyopathy Is Linked to 5' Terminal Genomic RNA-Deleted Viral Populations With Viral-Encoded Proteinase Activities.

BACKGROUND: Group B enteroviruses are common causes of acute myocarditis, which can be a precursor of chronic myocarditis and dilated cardiomyopathy, leading causes of heart transplantation. To date, the specific viral functions involved in the development of dilated cardiomyopathy remain unclear. METHODS: Total RNA from cardiac tissue of patients with dilated cardiomyopathy was extracted, and sequences corresponding to the 5' termini of enterovirus RNAs were identified. After next-generation RNA sequencing, viral cDNA clones mimicking the enterovirus RNA sequences found in patient tissues were generated in vitro, and their replication and impact on host cell functions were assessed on primary human cardiac cells in culture. RESULTS: Major enterovirus B populations characterized by 5' terminal genomic RNA deletions ranging from 17 to 50 nucleotides were identified either alone or associated with low proportions of intact 5' genomic termini. In situ hybridization and immunohistological assays detected these persistent genomes in clusters of cardiomyocytes. Transfection of viral RNA into primary human cardiomyocytes demonstrated that deleted forms of genomic RNAs displayed early replication activities in the absence of detectable viral plaque formation, whereas mixed deleted and complete forms generated particles capable of inducing cytopathic effects at levels distinct from those observed with full-length forms alone. Moreover, deleted or full-length and mixed forms of viral RNA were capable of directing translation and production of proteolytically active viral proteinase 2A in human cardiomyocytes. CONCLUSIONS: We demonstrate that persistent viral forms are composed of B-type enteroviruses harboring a 5' terminal deletion in their genomic RNAs and that these viruses alone or associated with full-length populations of helper RNAs could impair cardiomyocyte functions by the proteolytic activity of viral proteinase 2A in cases of unexplained dilated cardiomyopathy. These results provide a better understanding of the molecular mechanisms that underlie the persistence of EV forms in human cardiac tissues and should stimulate the development of new therapeutic strategies based on specific inhibitors of the coxsackievirus B proteinase 2A activity for acute and chronic cardiac infections.