Capsid-deficient alphaviruses generate propagative infectious microvesicles at the plasma membrane.
Alphavirus budding is driven by interactions between nucleocapsids assembled in the cytoplasm and envelope proteins present at the plasma membrane. So far, the expression of capsid and envelope proteins in infected cells has been considered an absolute requirement for alphavirus budding and propagation. In the present study, we show that Semliki Forest virus and Sindbis virus lacking the capsid gene can propagate in mammalian and insect cells. This propagation is mediated by the release of infectious microvesicles (iMVs), which are pleomorphic and have a larger size and density than wild-type virus. iMVs, which contain viral RNA inside and viral envelope proteins on their surface, are released at the plasma membrane and infect cells using the endocytic pathway in a similar way to wild-type virus. iMVs are not pathogenic in immunocompetent mice when injected intravenously, but can infect different organs like lungs and heart. Finally, we also show that alphavirus genomes without capsid can mediate the propagation of heterologous genes, making these vectors potentially interesting for gene therapy or vaccination studies. The minimalist infectious system described in this study shows that a self-replicating RNA able to express membrane proteins with binding and fusion properties is able to propagate, providing some insights into virus evolution.
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.|3P Biopharmaceuticals S.L., Noain, Spain.
Marta
M
Ruiz-Guillen
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.|Department of Experimental, Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy.
Evgeni
E
Gabev
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
Jose I
JI
Quetglas
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
Erkuden
E
Casales
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
María Cristina
MC
Ballesteros-Briones
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
Joanna
J
Poutou
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.|UFR des Sciences de la Santé Simone Veil, 2 avenue de la Source de la Bievre, 78180, Montugny-le-Bretonneux, France.
Alejandro
A
Aranda
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
Eva
E
Martisova
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.|Experimental Ophthalmology Laboratory, School of Medicine, University of Navarra, Pamplona, Spain.
Jaione
J
Bezunartea
Structural Biology Unit, CIC bioGUNE, CIBERehd, Bizkaia Technology Park, Derio, Spain.
Marina
M
Ondiviela
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.|Liver Unit, Clinica Universitaria de Navarra, CIBERehd, Pamplona, Spain.
Jesus
J
Prieto
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
Ruben
R
Hernandez-Alcoceba
Structural Biology Unit, CIC bioGUNE, CIBERehd, Bizkaia Technology Park, Derio, Spain.|IKERBASQUE, Basque Foundation for Science, Bilbao, Spain.
Nicola G A
NG
Abrescia
Division of Gene Therapy, CIMA, University of Navarra, Pamplona, Spain. csmerdou@unav.es.|IdiSNA, Navarra Institute for Health Research, Pamplona, Spain. csmerdou@unav.es.
Cristian
C
Smerdou
D000524:Alphavirus / Q000235:genetics / Q000472:pathogenicity*; D000818:Animals; D002213:Capsid / Q000378:metabolism*; D002459:Cell Fusion; D002460:Cell Line; D002462:Cell Membrane / Q000821:virology*; D055252:Cell-Derived Microparticles / Q000378:metabolism / Q000648:ultrastructure / Q000821:virology*; D005260:Female; D016679:Genome, Viral; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008810:Mice, Inbred C57BL; D009500:Neutralization Tests; D012367:RNA, Viral / Q000378:metabolism; D012672:Semliki forest virus / Q000472:pathogenicity; D014162:Transfection; D014759:Viral Envelope Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism
D012367:RNA, Viral; D014759:Viral Envelope Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins
Alphavirus; Capsid deficiency; Infectious microvesicles; Semliki Forest virus; Sindbis virus