HIV-Host Interactions

As adult, paediatric and adolescent HIV-1 infections continue to spread worldwide, the development of further anti-retroviral treatments remains of the utmost importance; for instance, there is no effective HIV-1 vaccine, and current front-line therapies targeting the viral reverse transcriptase and protease enzymes are compromised by compliance, toxicity and viral resistance concerns. Pursuing other HIV-1 (or human) proteins as targets for future anti-virals is therefore critical, but their rational selection requires a fundamental understanding of underlying biological principles. The replication of obligate intracellular parasites, such as HIV-1, is dependent upon the contributions of many host-derived factors and pathways. However, recent work from many laboratories, including our own, has shown that host cells also produce factors that are intrinsically anti-viral and are able to antagonise virus growth. This work focuses on three aspects of the cell?s natural armoury against HIV-1. First, we will continue our investigation of human APOBEC3G/F proteins, and how they suppress infection not only by inhibiting the copying of the viral genome, but also by introducing lethal mutations. Second, we will explore the biology of APOBEC3 proteins in terms of their contributions to cell physiology, and examine the contributions of cellular factors that interact with APOBEC3 proteins (such as the RNA silencing machinery), or accumulate in similar sites with cells, to virus replication. Third, we will characterise the response of human T cells to initial invasion by HIV-1 in terms of alterations in gene expression and the potential mobilisation of anti-viral mechanisms, and compare and contrast this effects with those of the broadly anti-viral type-1 interferons. Any therapeutic strategy that stimulates these proven/potential anti-viral mechanisms has the possibility of tipping the balance between facilitatory and inhibitory activities and thereby suppressing HIV-1 infection in the context of transmission between humans or established infection. The Public Relations Dept of KCL is primarily responsible for communicating our work to the public; and a ?Directory of Experts? is maintained that enables members of the public to identify academics willing to discuss specialist areas. For instance, MHM has given numerous interviews to the press, has appeared on television and has been consulted by the BBC on the content of AIDS-related programming. He is also a Section Editor of a public access journal, PLoS Pathogens, has given overview seminars on the value of scientific research at Community Liaison Meetings (e.g., Cafe Scientifique), and helps organise Conferences attended by non-scientific members of the HIV/AIDS community.

It is now recognised that animal cells express various factors and pathways that naturally inhibit the replication of viruses. The balance between these innate/intrinsic inhibitors and the many factors that promote replication helps establish the tempo of virus infection and, ultimately, contributes to disease outcome. Here, we outline an ambitious series of discovery-based and mechanistic experiments that will continue to build on our work on the anti-HIV-1 APOBEC3G/F proteins and will explore relationships between HIV-1 infection and other potential anti-viral networks, including the RNA silencing machinery, cellular stress-induced pathways, and the type-1 interferon (IFN) system. First, we will further define the mechanisms by which the APOBEC3 proteins suppress HIV-1 infection. In particular, we will determine how APOBEC3 proteins inhibit HIV-1 reverse transcription in primary CD4 T cells, using new assays to define the cDNAs of inhibited replication intermediates, to map interactions between APOBEC3G/F proteins and viral proteins and RNA, and to define the necessary participating attributes of the APOBEC3G/F proteins. Second, having demonstrated that APOBEC3G/F assemble into large cellular ribonucleoprotein (RNP) complexes, we will define the RNAs to which these proteins bind directly and address the impact of such interactions upon RNA fate and metabolism. Since APOBEC3G/F RNPs accumulate in RNA-rich cellular microdomains called P bodies (PBs) and stress granules (SGs), and some of the factors and complexes that also accumulate there (e.g., the RNA silencing machinery) have been implicated in the suppression of viral and transposon replication, we will investigate the importance of PB-, SG- or RNA silencing components in HIV-1 replication and APOBEC3G/F function. Third, we will use transcriptomic-based methodologies to define the initial (i.e., within hrs) response of CD4 T cells to HIV-1 challenge. Our preliminary results indicate that cells undergo substantial reprogramming, and that many of the induced host genes are also activated by type-1 IFN. Functional analyses will aim to identify cellular sensors of HIV-1 infection, as well as downstream signalling pathways and effector molecules. This work will be interpreted together with parallel studies where the mechanism by which IFN establishes an anti-HIV-1 state in T cells and macrophages is examined, and screens to isolate the contributing genes are undertaken. In sum, we aim to identify novel interactions between HIV-1 and infected host cells, with the goal of better understanding the principles of virus replication, pathogenesis and human cell biology, as well as defining rational targets for future therapeutic exploitation.