RNA structure duplication in the DENV genome: functional redundancy or host specificity

ANDREA V. GAMARNIK; HORACIO M. PALLARES; FRANCO L. MARSICO; IRMA SANCHEZ-VARGAS; CAROL BLAIR; CLAUDIA V. FILOMATORI; SERGIO M. VILLORDO; JUAN M. CARBALLEDA; LUANA DE BORBA

Galveston, TX

Congreso; 6th Pan American Dengue Network Meeting; 2018

University of Texas Medical Branch

The denguevirus (DENV) genome contains a single open reading frame flanked by two highly structured untranslatedregions (5' and 3'UTRs). The 3'UTR bears two pairs of duplicated RNA structures: two stem-loops (SLs) and two dumbbells (DBs), both involvedin highly stable structures, including tertiary interactions like pseudoknots (PK). We have previously shown that the two SLs havedifferent functions in vertebrates and invertebrate hosts. In this regard, ahost adaptable SL structure has been identified, which was associated to thegeneration of different species of sfRNAs. Interestingly, DENV isolated frominfected Aedes aegypti and Aedes albopictus, showed positiveselection of mutations in one of the two DB structures. In order to evaluate therelevance of this selection, we introduced the identified mutations in thecontext of an infectious clone and assessed viral replication in mosquito and human cells. The phenotype of the viruses obtained indicated that mutationsthat destabilize the PK of DB2 increase the ability of the virus to replicateonly in mosquito cells, explaining the natural selection of those mutations in mosquitoes,and providing evidence of different roles of this DB structure in the twohosts. Mechanistic studies designed to evaluate the function of the identifiedRNA elements supported the idea that the PK interaction of DB2 competes withgenome cyclization, reducing RNA synthesis. Thus, disruption of the PK may beresponsible for enhancement of viral replication in mosquito. Our data supportan antagonistic role of the two DBs, while the DB1 has been involved inpromoting genome cyclization (de Borba, etal. J. Virol., 2015), elements of DB2 compete with this RNA cyclization. Insummary, our studies indicate that each structure of the two pairs, SLs andDBs, play different functions during viral replication. In addition, each ofthese RNA elements displays specific roles in the two hosts.