RESUMO
HIV-1 integrase (IN) orchestrates the integration of the reverse transcribed viral cDNA into the host cell genome and participates also in other steps of HIV-1 replication. Cellular and viral factors assist IN in performing its multiple functions, and post-translational modifications contribute to modulate its activities. Here, we show that HIV-1 IN is modified by SUMO proteins and that phylogenetically conserved SUMOylation consensus motifs represent major SUMO acceptor sites. Viruses harboring SUMOylation site IN mutants displayed a replication defect that was mapped during the early stages of infection, before integration but after reverse transcription. Because SUMOylation-defective IN mutants retained WT catalytic activity, we hypothesize that SUMOylation might regulate the affinity of IN for co-factors, contributing to efficient HIV-1 replication.
Assuntos
Infecções por HIV/metabolismo , Integrase de HIV/metabolismo , HIV-1/fisiologia , Sumoilação/fisiologia , Integração Viral/fisiologia , Replicação Viral/fisiologia , Células HEK293 , Infecções por HIV/genética , Integrase de HIV/genética , Células HeLa , Humanos , Mutação , Transcrição Reversa/fisiologiaRESUMO
BACKGROUND: The Gag polyproteins play distinct roles during the replication cycle of retroviruses, hijacking many cellular machineries to fulfill them. In the case of the prototype foamy virus (PFV), Gag structural proteins undergo transient nuclear trafficking after their synthesis, returning back to the cytoplasm for capsid assembly and virus egress. The functional role of this nuclear stage as well as the molecular mechanism(s) responsible for Gag nuclear export are not understood. RESULTS: We have identified a leptomycin B (LMB)-sensitive nuclear export sequence (NES) within the N-terminus of PFV Gag that is absolutely required for the completion of late stages of virus replication. Point mutations of conserved residues within this motif lead to nuclear redistribution of Gag, preventing subsequent virus egress. We have shown that a NES-defective PFV Gag acts as a dominant negative mutant by sequestrating its wild-type counterpart in the nucleus. Trans-complementation experiments with the heterologous NES of HIV-1 Rev allow the cytoplasmic redistribution of FV Gag, but fail to restore infectivity. CONCLUSIONS: PFV Gag-Gag interactions are finely tuned in the cytoplasm to regulate their functions, capsid assembly, and virus release. In the nucleus, we have shown Gag-Gag interactions which could be involved in the nuclear export of Gag and viral RNA. We propose that nuclear export of unspliced and partially spliced PFV RNAs relies on two complementary mechanisms, which take place successively during the replication cycle.
Assuntos
Produtos do Gene gag/metabolismo , Sinais de Exportação Nuclear , Vírus Espumoso dos Símios/fisiologia , Replicação Viral , Núcleo Celular/metabolismo , Ácidos Graxos Insaturados/farmacologia , Produtos do Gene gag/genética , Células HEK293 , HIV-1/genética , Células HeLa , Humanos , Mutagênese Sítio-Dirigida , Mutação Puntual , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Produtos do Gene rev do Vírus da Imunodeficiência Humana/química , Produtos do Gene rev do Vírus da Imunodeficiência Humana/metabolismoRESUMO
Post-translational modifications, such as SUMOylation, are exam- ples of cellular machineries hijacked by viruses to efficiently replicate. SUMOylation, which consists in the conjugation of small ubiquitin-like modi- fier (SUMO) peptides to a substrate, is exploited or hampered by numerous viruses during infection. Several viral proteins are SUMOylated, causing modulation of sub-cellular localization, stability or modifications of protein activities. In this review, recently described viral examples have been chosen to highlight the different strategies used by viruses to hijack SUMOylation in order to promote replication. The link between pathologies due to viral infec- tions and SUMOylation is discussed. Finally, the potential applications of SUMOylation inhibitors in the treatment of viral infections and associated cancer are evoked.
RESUMO
Many cellular and viral proteins and nucleic acids shuttle between the nucleus and the cytoplasm. It is increasingly clear that nuclear import and export involve complex and finely regulated mechanisms. Nuclear export is absolutely necessary for viral protein synthesis and particle assembly for retroviruses showing a nuclear step during their replication cycle. Nuclear export of retroviral components mainly relies on two distinct mechanisms, one involving cellular factors only, and another in which cellular and viral factors cooperate. The study of retrovirus nuclear export contributes significantly to our understanding of the molecular mechanisms of nuclear export in general, and may allow the identification of new targets to prevent retrovirus replication.