Xiao-Jian Yao

Human immunodeficiency virus type 1 Vpr-mediated G2 cell cycle arrest: Vpr interferes with cell cycle signaling cascades by interacting with the B subunit of serine/threonine protein phosphatase 2A

The Vpr protein of primate lentiviruses arrests cell cycling at the G2/M phase through an inactivation of cyclin B–p34cdc2 and its upstream regulator cdc25. We provide here biochemical and functional evidence demonstrating that human immunodeficiency virus type 1 (HIV‐1) Vpr mediates G2 arrest by forming a complex with protein phosphatase 2A (PP2A), an upstream regulator of cdc25. Vpr associates with PP2A through a specific interaction with the B55 regulatory subunit. This interaction is necessary but not sufficient for G2 arrest. Interestingly, we found that Vpr association with B55‐containing PP2A targets the enzymatic complex to the nucleus and, importantly, enhances the recruitment and dephosphorylation of the cdc25 substrate. Our data suggest that Vpr mediates G2 arrest by enhancing the nuclear import of PP2A and by positively modulating its catalytic activity towards active phosphorylated nuclear cdc25.

Genetic Selection of Peptide Inhibitors of Human Immunodeficiency Virus Type 1 Vpr

Human immunodeficiency virus 1 (HIV-1) encodes a gene product, Vpr, that facilitates the nuclear uptake of the viral pre-integration complex in non-dividing cells and causes infected cells to arrest in the G2 phase of the cell cycle. Vpr was also shown to cause mitochondrial dysfunction in human cells and budding yeasts, an effect that was proposed to lead to growth arrest and cell killing in budding yeasts and apoptosis in human cells. In this study, we used a genetic selection in Saccharomyces cerevisiae to identify hexameric peptides that suppress the growth arrest phenotype mediated by Vpr. Fifteen selected glutathioneS-transferase (GST)-fused peptides were found to overcome to different extents Vpr-mediated growth arrest. Amino acid analysis of the inhibitory peptide sequences revealed the conservation of a di-tryptophan (diW) motif. DiW-containing GST-peptides interacted with Vpr in GST pull-down assays, and their level of interaction correlated with their ability to overcome Vpr-mediated growth arrest. Importantly, Vpr-binding GST-peptides were also found to alleviate Vpr-mediated apoptosis and G2 arrest in HIV-1-producing CD4+T cell lines. Furthermore, they co-localized with Vpr and interfered with its nuclear translocation. Overall, this study defines a class of diW-containing peptides that inhibit HIV-1 Vpr biological activities most likely by interacting with Vpr and interfering with critical protein interactions.