Browsing by Author "Alenquer, Marta"
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- Exosome Biogenesis, Regulation, and Function in Viral InfectionPublication . Alenquer, Marta; Amorim, MariaExosomes are extracellular vesicles released upon fusion of multivesicular bodies(MVBs) with the cellular plasma membrane. They originate as intraluminal vesicles (ILVs) duringthe process of MVB formation. Exosomes were shown to contain selectively sorted functionalproteins, lipids, and RNAs, mediating cell-to-cell communications and hence playing a role in thephysiology of the healthy and diseased organism. Challenges in the field include the identificationof mechanisms sustaining packaging of membrane-bound and soluble material to these vesicles andthe understanding of the underlying processes directing MVBs for degradation or fusion with theplasma membrane. The investigation into the formation and roles of exosomes in viral infection is inits early years. Although still controversial, exosomes can, in principle, incorporate any functionalfactor, provided they have an appropriate sorting signal, and thus are prone to viral exploitation.This review initially focuses on the composition and biogenesis of exosomes. It then explores theregulatory mechanisms underlying their biogenesis. Exosomes are part of the endocytic system,which is tightly regulated and able to respond to several stimuli that lead to alterations in thecomposition of its sub-compartments. We discuss the current knowledge of how these changesaffect exosomal release. We then summarize how different viruses exploit specific proteins ofendocytic sub-compartments and speculate that it could interfere with exosome function, althoughno direct link between viral usage of the endocytic system and exosome release has yet beenreported. Many recent reports have ascribed functions to exosomes released from cells infectedwith a variety of animal viruses, including viral spread, host immunity, and manipulation of themicroenvironment, which are discussed. Given the ever-growing roles and importance of exosomesin viral infections, understanding what regulates their composition and levels, and defining theirfunctions will ultimately provide additional insights into the virulence and persistence of infections.
- Influenza A virus ribonucleoproteins form liquid organelles at endoplasmic reticulum exit sitesPublication . Alenquer, Marta; Vale-Costa, Sílvia; Etibor, Temitope Akhigbe; Ferreira, Filipe; Sousa, Ana Laura; Amorim, Maria JoãoInfluenza A virus has an eight-partite RNA genome that during viral assembly forms a complex containing one copy of each RNA. Genome assembly is a selective process driven by RNA-RNA interactions and is hypothesized to lead to discrete punctate structures scattered through the cytosol. Here, we show that contrary to the accepted view, formation of these structures precedes RNA-RNA interactions among distinct viral ribonucleoproteins (vRNPs), as they assemble in cells expressing only one vRNP type. We demonstrate that these viral inclusions display characteristics of liquid organelles, segregating from the cytosol without a delimitating membrane, dynamically exchanging material and adapting fast to environmental changes. We provide evidence that viral inclusions develop close to endoplasmic reticulum (ER) exit sites, depend on continuous ER-Golgi vesicular cycling and do not promote escape to interferon response. We propose that viral inclusions segregate vRNPs from the cytosol and facilitate selected RNA-RNA interactions in a liquid environment.
- Influenza A virus ribonucleoproteins modulate host recycling by competing with Rab11 effectorsPublication . Vale-Costa, Sílvia; Alenquer, Marta; Sousa, Ana Laura; Kellen, Bárbara; Ramalho, José; Tranfield, Erin M.; Amorim, Maria JoãoInfluenza A virus assembly is an unclear process, whereby individual virion components form an infectious particle. The segmented nature of the influenza A genome imposes a problem to assembly because it requires packaging of eight distinct RNA particles (vRNPs). It also allows genome mixing from distinct parental strains, events associated with influenza pandemic outbreaks. It is important to public health to understand how segmented genomes assemble, a process that is dependent on the transport of components to assembly sites. Previously, it has been shown that vRNPs are carried by recycling endosome vesicles, resulting in a change of Rab11 distribution. Here, we describe that vRNP binding to recycling endosomes impairs recycling endosome function, by competing for Rab11 binding with family-interacting proteins, and that there is a causal relationship between Rab11 ability to recruit family-interacting proteins and Rab11 redistribution. This competition reduces recycling sorting at an unclear step, resulting in clustering of single- and double-membraned vesicles. These morphological changes in Rab11 membranes are indicative of alterations in protein and lipid homeostasis during infection. Vesicular clustering creates hotspots of the vRNPs that need to interact to form an infectious particle.
- KIF13A mediates influenza a virus ribonucleoproteins traffickingPublication . Ramos-Nascimento, Ana; Kellen, Bárbara; Ferreira, Filipe; Alenquer, Marta; Vale-Costa, Silvia; Raposo, Graça; Delevoye, Cédric; Amorim, Maria JoãoInfluenza A is a rapid evolving virus, successful in provoking periodic epidemics and occasional pandemics in humans. Viral assembly is complex as the virus incorporates an eight-partite segmented genome of RNA (in the form of viral ribonucleoproteins, vRNPs). Genome assembly, with implications to public health, is not completely understood. It was reported that vRNPs are transported to the cell surface on Rab11 vesicles using microtubules, but no molecular motor has been assigned to the process. Here, we have identified KIF13A, a member of the kinesin-3 family, as the first molecular motor efficiently transporting vRNP-Rab11 vesicles during IAV infection. Depletion of KIF13A resulted in reduced viral titres and less accumulation of vRNPs at the cell surface, without interfering with the levels of other viral proteins at sites of viral assembly. In addition, in overexpression conditions and using two artificial methods able to displace vRNP-Rab11 vesicles, KIF13A augmented vRNP levels at the plasma membrane. Together our results show that KIF13A is an important host factor promoting influenza A vRNP transport, which is a crucial step for viral assembly.