HIV-1 integrase SUMOylation and viral replication
© Zamborlini et al; licensee BioMed Central Ltd. 2011
Published: 3 October 2011
HIV-1 integrase catalyzes the integration of the reverse transcribed viral cDNA into the cellular genome, a key event of retroviral replication that is targeted by novel anti-HIV therapeutic agents. Numerous studies have contributed to understand of the molecular basis of integrase catalytic functions. Besides integration, HIV-1 integrase participates in other steps of viral replication such as reverse transcription and/or uncoating, PIC nuclear import and virion morphology. However, the underlying mechanisms are still not fully elucidated. Cellular and viral factors assist integrase in performing its multiple activities. Moreover, post-translational modifications (i.e. acetylation, ubiquitination and phosphorylation), which represent a common, rapid and generally reversible mechanism for fine tuning of protein activities, have also been shown to regulate integrase functions.
Materials and methods and results
By in vitro SUMOylation assay and purification on Ni-NTA beads in denaturing conditions, we show that HIV-1 integrase is covalently modified by the three SUMO paralogues. By mutating SUMO-acceptor lysine residues within phylogenetically conserved SUMOylation consensus motifs identified in silico, we demonstrate that they represent major sites of SUMO conjugation. We introduced the same changes in the integrase sequence of a plasmid encoding the viral genome, which was used to generate mutant viral particles, and we compare their infectivity to that of WT HIV-1. We find that viruses harboring SUMOylation-defective integrase mutants are less infectious that the WT counterpart. Real-time PCR analysis of viral cDNA synthesis reveals that cells infected with mutant viruses display similar content of traverse transcripts, but a lower number of integrated proviruses, than WT HIV-1-infected cells. This integration defect at the integration step is not due to impairment of integrase binding to LEDGF/p7S, a key chromatin-tethering factor of HIV-1 pre-integration complex. Indeed, both WT and SUMOylation-defective integrase proteins coprecipitated with similar efficiency with LEDGF/p75. Finally, we establish that SUMOylation-defective integrase mutants retained WT catalytic activity as determined by Vpr-fusion protein complementation assay.
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. Since SUMOylation-defective IN mutants retained WT catalytic activity as well as LEDGF-binding, we hypothesize that SUMOylation might regulate the affinity of IN for co-factors, contributing to efficient HIV-1 replication.
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