6 research outputs found
Amino acids substitutions in Ï1 and ÎŒ1 outer capsid proteins of a Vero cell-adapted mammalian orthoreovirus are required for optimal virus binding and disassembly
In a recent study, the serotype 3 Dearing strain of mammalian orthoreovirus was adapted to Vero cells; cells that exhibit a limited ability to support the early steps of reovirus uncoating and are unable to produce interferon as an antiviral response upon infection. The Vero cell-adapted virus (VeroAV) exhibits amino acids substitutions in both the Ï1 and ÎŒ1 outer capsid
proteins but no changes in the Ï3 protein. Accordingly, the virus was shown not to behave as a classical uncoating mutant. In the present study, an increased ability of the virus to bind at the Vero cell surface was observed and is likely associated with an increased ability to bind onto cell-surface sialic acid residues. In addition, the kinetics of ÎŒ1 disassembly from the
virions appears to be altered. The plasmid-based reverse genetics approach confirmed the importance of Ï1 amino acids substitutions in VeroAV's ability to efficiently infect Vero cells, although ÎŒ1 co-adaptation appears necessary to optimize viral infection. This approach of combining in vitro selection of reoviruses with reverse genetics to identify pertinent amino
acids substitutions appears promising in the context of eventual reovirus modification to increase its potential as an oncolytic virus.Dans une Ă©tude rĂ©cente, le rĂ©ovirus de sĂ©rotype 3 (souche Dearing) a Ă©tĂ© adaptĂ© aux cellules Vero, cellules qui possĂšdent une capacitĂ© limitĂ©e Ă supporter les Ă©tapes prĂ©coces de dĂ©capsidation de rĂ©ovirus et qui sont incapables de produire de l'interfĂ©ron comme rĂ©ponse antivirale lorsqu'elles sont infectĂ©es. Le virus adaptĂ© (VeroAV) possĂšde des substitutions d'acides aminĂ©s au niveau des protĂ©ines de capside externe Ï1 et ÎŒ1, mais ne prĂ©sente pas de changement au niveau de la protĂ©ine Ï3. Comme attendu, le virus ne se comporte donc pas comme un mutant de dĂ©capsidation classique. Dans la prĂ©sente Ă©tude, une augmentation de la capacitĂ© du virus Ă se fixer Ă la surface des cellules Vero a Ă©tĂ© observĂ©e et est probablement associĂ©e Ă une augmentation de la fixation aux acides sialiques de la surface cellulaire. De plus, la cinĂ©tique de relĂąche de ÎŒ1 Ă partir des virions semble altĂ©rĂ©e. L'approche de gĂ©nĂ©tique inverse a permis de confirmer l'importance des substitutions d'acides aminĂ©s de la protĂ©ine Ï1 dans la capacitĂ© de VeroAV Ă infecter les cellules Vero de maniĂšre efficace, bien que la coadaptation de ÎŒ1 apparaisse nĂ©cessaire pour optimiser l'infection virale. Cette approche combinant la sĂ©lection in vitro de rĂ©ovirus Ă la gĂ©nĂ©tique inverse pour dĂ©couvrir des substitutions importantes d'acides aminĂ©s apparaĂźt prometteuse dans le contexte de la modification de rĂ©ovirus afin d'accroĂźtre son potentiel en tant que virus oncolytique.Conseil de recherches en sciences naturelles et en gĂ©nie du Canad
Combinaison dâapproches classiques et de gĂ©nĂ©tique inverse en vue d'une meilleure comprĂ©hension du tropisme et de l'activitĂ© oncolytique du rĂ©ovirus de mammifĂšres
Le réovirus de mammifÚres se multiplie et détruit préférentiellement les cellules
cancĂ©reuses. Il est dâailleurs actuellement Ă lâĂ©tude pour traiter divers types de cancers
chez lâhumain. Lâobjectif de cette Ă©tude Ă©tait de mieux comprendre les diverses
composantes impliquĂ©es dans le cycle viral de rĂ©ovirus qui pourraient potentiellement ĂȘtre
importantes dans le contexte dâoptimisation de son potentiel oncolytique, ceci en utilisant
une combinaison dâapproches classiques ainsi que de gĂ©nĂ©tique inverse.Lâapproche par persistance virale est classiquement utilisĂ©e pour identifier de
nouveaux mutants de réovirus. Celle-ci a surtout mené à la sélection de mutants de
décapsidation chez les cellules L929. Ici, des virus adaptés furent récupérés de cellules
Vero (VeroAV) et contrairement aux autres mutants de persistance, ce virus possĂšde des
substitutions dâacides aminĂ©s sur les protĂ©ines mu1 et sigma1. Lâapproche par gĂ©nĂ©tique
inverse a permis de démontrer que la fixation de VeroAV sur les acides sialiques des
cellules Vero était favorisée. Les substitutions sur sigma1 seraient principalement
responsables de ce phénotype quoique le contexte de la substitution de mu1 puisse
affecter lâinfectivitĂ© du virus.
Dans un deuxiÚme volet, il a été remarqué que le virus de type sauvage utilisé pour
la gĂ©nĂ©tique inverse (T3DK) Ă©tait plus sensible Ă lâinterfĂ©ron comparativement au virus de
type sauvage de notre laboratoire (T3DS). AprÚs séquençage complet du virus T3DS nous
avons reconstruit, par génétique inverse, le virus T3DS. Nous avons donc pu poursuivre
nos études sur le virus P4L-12 précédemment isolé au laboratoire par mutagenÚse
chimique. Il a été préalablement démontré que P4L-12 possÚde une meilleure réplication
chez les cellules transformées et un blocage plus complet chez les cellules parentales,
phĂ©notype reliĂ© Ă une sensibilitĂ© accrue Ă lâinterfĂ©ron. Dans cette Ă©tude, des substitutions
dâacides aminĂ©s sur les protĂ©ines sigma3, mu1, muNS et lambda2 furent identifiĂ©s. Nous
avons démontré, par génétique inverse, que la substitution sur la protéine lambda2 était
principalement responsable du phĂ©notype de sensibilitĂ© Ă lâinterfĂ©ron. Ces approches de persistance ou de sĂ©lection de mutants sensibles Ă lâinterfĂ©ron,
suivies dâune caractĂ©risation par gĂ©nĂ©tique inverse seront certainement utiles Ă une
meilleure compréhension de réovirus et pourraient contribuer à améliorer son potentiel
oncolytique.The mammalian reovirus preferentially replicates and kills cancer cells. It is
therefore currently used in clinical trials to treat various types of cancers in humans. The
main objective of this study was to get a better understanding of the various components
involved in the reovirus replication cycle that could potentially be important for the
optimization of its oncolytic properties using a combination of traditional approaches and
the newly described reverse genetics technique. Classically, the viral persistence approach is undertaken to identify new reovirus
variants. This has led to the selection of uncoating mutants in L929 cells. In this study,
adapted viruses were recovered from Vero cells (VeroAV) and unlike other persistence
mutants, VeroAV had amino acid substitutions on the mu1 and the sigma1 proteins. The
reverse genetics approach demonstrated that VeroAV had a better binding ability onto
sialic acids of Vero cells. Substitutions on sigma1 were found to be mainly responsible for
this phenotype although mu1 substitutions may affect virus infectivity.
In a second study, we noticed that the reverse genetics wild-type virus (T3DK) was
more sensitive to interferon when compared with the wild-type virus from our laboratory
(T3DS). After complete sequencing of the T3DS, we then constructed a T3DS by reverse
genetics. This allowed us to proceed in our studies of a mutant virus previously recovered
in our laboratory by chemical mutagenesis (P4L-12). It was previously established that
P4L-12 had an enhanced replication in transformed cells while sparing the parental cells
and this phenotype was correlated to an increased sensitivity to interferon. In this study,
amino acid substitutions on the sigma3, mu1, muNS and lambda2 proteins were
identified. By using the reverse genetics approach, we demonstrated that the substitution
found on the lambda2 protein was primarily responsible for the increase in sensitivity to
interferon of P4L-12.
The combination of approaches based on persistence or selection of mutants
sensitive to interferon followed by characterization with reverse genetics will certainly be
useful to get a better understanding of reovirus in order to improve its oncolytic capacity
A single amino acid substitution in the mRNA capping enzyme λ2 of a mammalian orthoreovirus mutant increases interferon sensitivity
In the last few years, the development of a plasmid-based reverse genetics system for mammalian reovirus has allowed the production and characterization of mutant viruses. This could be especially significant in the optimization of reovirus strains for virotherapeutic applications, either as gene vectors or oncolytic viruses. The genome of a mutant virus exhibiting increased sensitivity to interferon was completely sequenced and compared with its parental virus. Viruses corresponding to either the parental or mutant viruses were then rescued by reverse genetics and shown to exhibit the expected phenotypes. Systematic rescue of different viruses harboring either of the four parental genes in a mutant virus backbone, or reciprocally, indicated that a single amino acid substitution in one of λ2 methyltransferase domains is the major determinant of the difference in interferon sensitivity between these two viruses.Au cours des derniĂšres annĂ©es, la mise au point de la gĂ©nĂ©tique inverse pour les rĂ©ovirus de mammifĂšres a permis la production et la caractĂ©risation de virus mutants. Ceci pourrait ĂȘtre spĂ©cialement important pour l'optimisation de souches virales en vue d'applications thĂ©rapeutiques, comme vecteurs de gĂšnes ou virus oncolytiques. Le gĂ©nome d'un virus mutant dĂ©montrant une sensibilitĂ© accrue Ă l'interfĂ©ron a Ă©tĂ© complĂštement sĂ©quencĂ© et comparĂ© au virus parental. Des virus correspondant au virus parental ou mutant ont ensuite Ă©tĂ© rĂ©cupĂ©rĂ©s par gĂ©nĂ©tique inverse et prĂ©sentaient les phĂ©notypes attendus. La rĂ©cupĂ©ration systĂ©matique de diffĂ©rents virus possĂ©dant un des quatre gĂšnes parentaux dans un fond gĂ©nĂ©tique du virus mutant, et rĂ©ciproquement, a indiquĂ© qu'une seule substitution d'acide aminĂ© dans un des deux domaines mĂ©thyltransfĂ©rase de λ2 est le dĂ©terminant majeur de la diffĂ©rence de sensibilitĂ© Ă l'interfĂ©ron entre ces deux virus.Conseil de recherches en sciences naturelles et en gĂ©nie du Canada
Amino acid substitutions in Ï1 and ÎŒ1 outer capsid proteins are selected during mammalian reovirus adaptation to Vero cells
Establishment of viral persistence in cell culture has previously led to the selection of mammalian reovirus mutants, although very few of those have been characterized in details. In the present study, reovirus was adapted to Vero cells that, in contrast to classically-used L929 cells, are inefficient in supporting the early steps of reovirus uncoating and are also unable to produce interferon as an antiviral response once infection occurs. The Vero cell-adapted reovirus exhibits amino acids substitutions in both the Ï1 and ÎŒ1 proteins. This contrasts with uncoating mutants from persistently-infected L929 cells, and various other cell types, that generally harbor amino acids substitutions in the Ï3 outer capsid protein. The Vero cell-adapted virus remained sensitive to an inhibitor of lysosomal proteases; furthermore, in the absence of selective pressure for its maintenance, t he virus has partially lost its ability to resist interferon. The positions of the amino acids substitutions on the known protein structures suggest an effect on binding of the viral Ï1 protein to the cell surface and on ÎŒ1 disassembly from the outer capsid.L'Ă©tablissement de la persistance virale en culture cellulaire a prĂ©cĂ©demment menĂ© Ă la sĂ©lection de mutants de rĂ©ovirus, bien que peu d'entre eux aient Ă©tĂ© caractĂ©risĂ©s en dĂ©tail. Dans la prĂ©sence Ă©tude, le rĂ©ovirus a Ă©tĂ© adaptĂ© aux cellules Vero qui, contrairement aux cellules L929 classiquement utilisĂ©es, sont peu efficaces pour les Ă©tapes prĂ©coces de dĂ©capsidation de rĂ©ovirus et sont Ă©galement incapables de produire de l'interfĂ©ron comme rĂ©ponse antivirale, lorsqu'infectĂ©es. Le rĂ©ovirus adaptĂ© aux cellules Vero porte des substitutions d'acides aminĂ©s Ă la fois dans les protĂ©ines Ï1 et ÎŒ1. Ceci contraste avec les mutants de dĂ©capsidation des cellules L929 infectĂ©es de maniĂšre persistante, aussi bien que chez divers autres types de cellules, qui prĂ©sentent gĂ©nĂ©ralement des substitutions d'acides aminĂ©s au niveau de la protĂ©ine de capside externe Ï3. Le virus adaptĂ© aux cellules Vero demeure sensible Ă un inhibiteur de protĂ©ases lysosomales; de plus, en absence de pression de sĂ©lection, le virus a perdu en partie sa capacitĂ© Ă rĂ©sister Ă l'interfĂ©ron. La position des diffĂ©rentes substitutions d'acides aminĂ©s sur la structure connue de la protĂ©ine suggĂšre un effet sur la fixation de la protĂ©ine virale Ï1 Ă la surface cellulaire et sur l'Ă©limination de la protĂ©ine ÎŒ1 de la capside externe du virus.Conseil de recherches en sciences naturelles et en gĂ©nie du Canad
Transient high level mammalian reovirus replication in a bat epithelial cell line occurs without cytopathic effect
Mammalian reoviruses exhibit a large host range and infected cells are generally killed;
however, most studies examined only a few cell types and host species, and are probably not
representative of all possible interactions between virus and host cell. Many questions thus
remain concerning the nature of cellular factors that affect viral replication and cell death. In
the present work, it was observed that replication of the classical mammalian reovirus serotype
3 Dearing in a bat epithelial cell line, Tb1.Lu, does not result in cell lysis and is rapidly
reduced to very low levels. Prior uncoating of virions by chymotrypsin treatment, to generate
infectious subviral particles, increased the initial level of infection but without any significant
effect on further viral replication or cell survival. Infected cells remain resistant to virus
reinfection and secrete an antiviral factor, most likely interferon, that is protective against the
unrelated encephalomyocarditis virus. Although, the transformed status of a cell is believed to
promote reovirus replication and viral âoncolysisâ, resistant Tb1.Lu cells exhibit a classical
phenotype of transformed cells by forming colonies in semisolid soft agar medium. Further
transduction of Tb.Lu cells with a constitutively-active Ras oncogene does not seem cell
growth or reovirus effect on these cells. Infected Tb1.Lu cells can produce low-level of
infectious virus for a long time without any apparent effect, although these cells are resistant to
reinfection. The results suggest that Tb1.Lu cells can mount an unusual antiviral response.
Specific properties of bat cells may thus be in part responsible for the ability of the animals to
act as reservoirs for viruses in general and for novel reoviruses in particular. Their peculiar
resistance to cell lysis also makes Tb1.Lu cells an attractive model to study the cellular and
viral factors that determine the ability of reovirus to replicate and destroy infected cells.Les rĂ©ovirus de mammifĂšres possĂšdent un large spectre d'hĂŽtes et les cellules infectĂ©es sont gĂ©nĂ©ralement tuĂ©es par l'infection ; cependant, la plupart des Ă©tudes utilisent seulement certains types de cellules provenant de quelques espĂšces animales. Ceci n'est sans doute pas reprĂ©sentatif de toutes les interactions possibles entre virus et cellule hĂŽte. Plusieurs questions demeurent concernant la nature des facteurs cellulaires qui affectent la rĂ©plication virale et la mort cellulaire. Dans la prĂ©sente Ă©tude, il a Ă©tĂ© observĂ© que la rĂ©plication du classique rĂ©ovirus de mammifĂšres (sĂ©rotype 3 Dearing) dans une lignĂ©e de cellules Ă©pithĂ©liales de chauve-souris, Tb1.Lu, n'entraĂźne pas la lyse cellulaire et est rapidement rĂ©duite Ă un trĂšs faible niveau. La dĂ©capsidation des virions par traitement Ă la chymotrypsine, afin de gĂ©nĂ©rer des particules dites « sous-virales infectieuses », augmente le niveau initial d'infection sans effet significatif sur la rĂ©plication virale ou la survie cellulaire. Les cellules infectĂ©es demeurent rĂ©sistantes Ă la rĂ©infection et sĂ©crĂštent un facteur antiviral, probablement de l'interfĂ©ron, qui peut protĂ©ger contre l'infection par le virus de l'encĂ©phalomyocardite. MalgrĂ© le fait que le statut de transformation cellulaire est considĂ©rĂ© comme pouvant promouvoir la rĂ©plication de rĂ©ovirus et l'oncolyse virale, les cellules Tb1.Lu rĂ©sistantes dĂ©montrent un phĂ©notype classique de cellules transformĂ©es et forment des colonies en milieu semi-solide contenant de l'agar. La transduction de cellules Tb1.Lu avec un oncogĂšne Ras constitutivement actif ne semble pas affecter la croissance cellulaire ni la rĂ©plication virale. Les cellules Tb1.Lu infectĂ©es peuvent produire une faible quantitĂ© de virus infectieux pour une longue pĂ©riode sans effet apparent, malgrĂ© le fait que ces cellules soient rĂ©sistantes Ă la rĂ©infection. Ces rĂ©sultats suggĂšrent que les cellules Tb1.Lu peuvent dĂ©velopper une rĂ©ponse antivirale inhabituelle. Les propriĂ©tĂ©s spĂ©cifiques des cellules de chauve-souris pourraient donc ĂȘtre en partie responsables de la capacitĂ© de ces animaux Ă agir comme rĂ©servoirs de virus en gĂ©nĂ©ral et de nouveaux rĂ©ovirus en particulier. Leur rĂ©sistance particuliĂšre Ă la lyse cellulaire fait aussi de ces cellules un modĂšle attrayant pour Ă©tudier les facteurs cellulaires et viraux qui dĂ©terminent la capacitĂ© de rĂ©ovirus Ă se rĂ©pliquer et Ă dĂ©truire les cellules infectĂ©es.Conseil de recherches en sciences naturelles et en gĂ©nie du Canad