Identification of Cellular Proteins and Molecular Mechanisms that Contribute to HIV-1 Latency and Evasion of Immunoregulation

The existence of long-lasting cellular reservoirs of HIV-1 is one the major hurdles in developing effective anti-retroviral therapies. These latently infected cells and tissues efficiently evade immune responses and viral replication remains dormant until activated, at which time the cell can generate a productive HIV-1 infection. This classic scenario of viral latency becomes even more difficult to study and model due to the extreme complexity of translating in vivo virus-cell interactions into a controlled in vitro system. A favorable approach to identify preventative therapeutic targets throughout the past few years has involved the search for disease biomarkers within human peripheral fluids. The comparison of normal versus disease states can identify an overexpression or a suppression of critical proteins where illness has directly altered a patient's cellular homeostasis. In particular, the analysis of HIV-1 infected serum is an attractive medium with which to identify altered protein expression due to the ease and non-invasive methods of collecting samples as well as the corresponding insight into the in vivo interaction of the virus with infected cells/tissue. The utilization of proteomic techniques to globally identify differentially expressed serum proteins in response to HIV-1 infection is hindered by the complexity of human serum. Here, we have identified unique serum proteins that are differentially expressed in HIV-1 long term non-progressors and may contribute to the ability of these patients to combat HIV-1 infection in the absence of antiretroviral therapy. Specifically, it was observed that the endogenous cdk inhibitor p16INK4A, an integral member of the Rb-tumor suppressor pathway, suppressed viral replication and induce apoptosis in HIV-1 infected cell lines. Interestingly, a large body of literature exists regarding utilizing pharmacological cdk inhibitors as HIV-1 therapeutics. We show that both HIV-1 Tat-derived small peptide cdk inhibitors and small molecular peptide mimetic cdk inhibitors are able to suppress viral replication both in vitro and in an in vivo humanized mouse model of HIV-1 infection. Recent developments and constant improvements upon hematopoietic engraftment of human cells and tissues onto recipient immunocompromised murine scaffolds have made it possible to model complex human innate and adaptive immune responses in a small animal model. Finally, we attempted to characterize the dysregulation of the Rb protein in the context of HIV-1 infection. We found that Rb is hyper-phosphorylated in HIV-1 chronically infected cell lines, indicative of a functionally inactive state, therefore supporting unchecked proliferation. However, functionally active Rb can rescue the replicative, transcriptional, and proliferative manipulation imparted on a cell due to HIV-1 infection. Utilizing a global proteomics approach to characterize novel protein expression profiles of HIV-1 latently infected individuals, we have demonstrated a robust dysregulation of the Rb pathway in chronically infected cells, therefore identifying possible therapeutic targets and providing an interesting insight as to the molecular mechanism of HIV-1 latency.