E17A mutation in HIV-1 Vpr confers resistance to didanosine in association with thymidine analog mutations

BACKGROUND

HIV-1 accessory Vpr protein is involved in the reverse transcription process and has been shown to modulate the virus mutation rate. This process may play a role in the kinetics of appearance of drug resistance mutations under antiretroviral treatment.

METHODS

Vpr sequences were analyzed from plasma viruses derived from 97 HIV-1-infected individuals failing antiretroviral treatment and 63 antiretroviral-naïve patients. Vpr genetic variability was analyzed for association with specific drug treatment and drug resistance mutations. Biological and virological experiments were employed to characterize a mutation in Vpr found to be associated with virological failure.

RESULTS

E17A mutation located in the first α-helix of Vpr was more prevalent in HAART-treated individuals compared to untreated individuals. E17A was associated with thymidine analog mutations (TAMs) in reverse transcriptase M41L, L210W and T215Y and with the use of didanosine in the patients' treatment histories. E17A had no impact on the biochemical and functional properties of Vpr, and did not affect kinetics of replication of wild-type or TAMs-containing viruses. However, its association with TAMs and the use of didanosine was consistent with phenotypic susceptibility assays showing a significant 3-fold decrease in didanosine susceptibility of viruses harboring Vpr E17A combined with TAMs compared to viruses harboring TAMs alone.

CONCLUSION

These findings highlight a novel role of Vpr in HIV-1 drug resistance. Vpr E17A confers resistance to didanosine when associated with TAMs. Whether Vpr E17A facilitates excision of didanosine is still to be determined.

Molecular and functional basis for the scaffolding role of the p50/dynamitin subunit of the microtubule-associated dynactin complex

p50/dynamitin (DM) is a major subunit of the microtubule-associated dynactin complex that is required for stabilization and attachment of its two distinct structural domains, namely the Arp1 rod and the shoulder/sidearm. Here, we define the determinants of p50/DM required for self-oligomerization of the protein and for interactions with other subunits of the dynactin complex. Whereas the N-terminal 1-91-amino acid region of the protein is required and sufficient for binding to the Arp1 rod, additional determinants contained within the first half of the protein are required for optimal recruitment of the p150(Glued) subunit of the shoulder/sidearm. Overexpression experiments confirmed that the N-terminal 1-91-amino acid region of p50/DM is critical for dynactin functionality, because this fragment acts as a dominant negative to inhibit both dynein-dependent and -independent functions of the complex. Furthermore, the first two predicted coiled-coil motifs of p50/DM contain determinants that mediate self-association of the protein. Interestingly, p50/DM self-association does not contribute to p50/DM-induced disruption of the dynactin complex, but most likely participates in the stabilization of the complex.

Characterization of the molecular determinants of primary HIV-1 Vpr proteins: impact of the Q65R and R77Q substitutions on Vpr functions

Although HIV-1 Vpr displays several functions in vitro, limited information exists concerning their relevance during infection. Here, we characterized Vpr variants isolated from a rapid and a long-term non-progressor (LTNP). Interestingly, vpr alleles isolated from longitudinal samples of the LTNP revealed a dominant sequence that subsequently led to diversity similar to that observed in the progressor patient. Most of primary Vpr proteins accumulated at the nuclear envelope and interacted with host-cell partners of Vpr. They displayed cytostatic and proapoptotic activities, although a LTNP allele, harboring the Q65R substitution, failed to bind the DCAF1 subunit of the Cul4a/DDB1 E3 ligase and was inactive. This Q65R substitution correlated with impairment of Vpr docking at the nuclear envelope, raising the possibility of a functional link between this property and the Vpr cytostatic activity. In contradiction with published results, the R77Q substitution, found in LTNP alleles, did not influence Vpr proapoptotic activity.