Van Tulleken, CR; (2017) Characterisation of Lentiviral Vpr Function and Mechanism. Doctoral thesis , UCL (University College London).

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Abstract

Genetic conflict between viruses and their hosts has driven an ‘arms race’, forcing the evolution of both immune defencesdefenses and multiple viral strategies to counteract and evade them. In the case of HIV many of these processes are well characterised – the virus carries with it a set of accessory proteins which target specific host restriction factors. Of these accessory proteins Vpr is the least well understood, with no described role that adequately explains its conservation across all known primate lentiviruses. Unpublished data from our lab indicate that Vpr is able to rescue infection in macrophages from addition of cGAMP, a second messenger protein produced by the cytosolic DNA sensor cGAS which activates antiviral immune signalling pathways. This study first sought to test the hypothesis that Vpr has evolved to counteract cGAS/STING mediated cytosolic DNA sensing using a co-transfection assay to test Vpr proteins from all groups of primate lentiviruses. Initial observations appeared to demonstrate specific degradation of innate immune signalling proteins. It was subsequently shown that HIV-1 M Vpr antagonises expression from all tested co-transfected plasmids. This phenotype was demonstrated to be species specific, and to correlate with both the history of zoonotic transmission and localisation of Vpr to the nuclear rim. Additionally, it was shown that Vpr antagonises NFB signalling activated by TNF, independent of an effect on expression from transfected plasmids, but with the same dependence on nuclear localisation, putatively by the same mechanism. Next, this study characterised an observation that the Vpr from the lentivirus infecting a mona monkey (SIVmon) stimulates NFB signalling. It was hypothesised that the SIVmon Vpr might have molecular binding partners in common with the HIV-1 M Vpr and conditions were optimised for proteomics studies to determine these binding partners. This study provides insights into the role of Vpr in antagonising innate immune sensing. Additionally, overexpression assays have been used widely in the literature describing Vpr. The data presented here indicate that observations using these assays, apparently demonstrating specific degradation of host cellular proteins, should be interpreted cautiously.

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