According to United Nations statistics, 42 million people are living with HIV/AIDS globally with an estimated 14,000 new infections and 8,500 deaths occurring every day. A number of antiviral drugs have been developed and are being used to extend the lives of many HIV infected individuals. Many of these compounds are however not well tolerated by patients, and the highly mutable virus can quickly develop resistance to the drugs with little loss of fitness.
Presently available anti-viral drugs were designed to counteract the best-understood HIV functions. These include protease-mediated cleavage of viral components, entry, reverse transcription and integration. These targets were experimentally most accessible because their activities parallel those of cellular homologs. The similarities made deciphering the proteins' functions easier but also made development of high specificity drugs more difficult.
A number of evolutionarily conserved proteins among the 15 encoded by HIV may serve as highly suitable alternative antiviral targets, specifically by virtue of their difference from cellular components. Determining the role that each viral protein plays in HIV infection will provide vital insight into how HIV evades and cripples the immune system.
The focus of research in our laboratory is on how one of these HIV-1 proteins, designated Vpr, contributes to virus replication and pathogenesis. Vpr has two known biological functions. One function is to halt the cell cycle at or near the G2 phase, specifically after most or all cellular DNA has been duplicated but before cell division. The other function is to promote infection of non-dividing cells. This role may be related to the Vpr-encoded nuclear import and export signals, but alternative possibilities are rapidly emerging. Interestingly, the capacities to cause cell cycle arrest and to promote virus replication in non-dividing cells are separated on two related proteins, Vpr and Vpx respectively, in HIV-2 and some simian immunodeficiency virus counterparts.
We and others have demonstrated that HIV1 and HIV2 Vpr as well as HIV2 Vpx engage a ubiquitin ligase complex which is characterized by inclusion of the proteins DDB1 and cullin4A. Further we found that Vpr uses the protein DCAF1 as an adapter to the engage the ubiquitin ligase complex. Blocking the function of this complex in various ways prevented Vpr from triggering G2 cell cycle arrest but did not interfere detectably with normal cell cycle progression or with the ability of the cells to arrest in response to DNA damage. We are presently working to identify the cellular target or targets of this ubiquitin ligase complex. Our long-term goal is to determine how the interaction between Vpr and the ubiquitin ligase complex impacts HIV replication and pathogenesis.