The principal goal of this project is to understand the impact of HIV envelope-mediated signaling on viral replication and immune dysfunction. This information may facilitate the discovery of new strategies for the treatment of HIV infection. HIV envelope proteins, which are displayed on the surface of viral particles, bind to two receptors on T-lymphocytes in order to infect those cells. Initially envelope proteins on the outer surface of virions dock with the CD4 receptor, and subsequently they engage a co-receptor, either CCR5 or CXCR4. Envelope engagement of each of these receptors results in signal transduction; however the consequences associated with those signals is only partially understood. In previous studies we demonstrated that HIV envelope-mediated signaling induces several biological responses in primary T-cells and macrophages, including the induction of expression of proinflammatory cytokines and increased rates of apoptosis. ? ? To obtain a more complete picture of the effect of envelope on the function and metabolic state of peripheral blood mononuclear cells (PBMCs), we developed an experimental strategy in which PBMCs from healthy donors were exposed to HIV envelope, and changes in the transcriptional program were determined using high-density oligonucleotide microarrays. HIV envelopes derived from different isolates vary in their primary sequence. In order to understand the relevance of sequence variation to envelope signaling, a panel of envelopes representing each of the five major sub-types of HIV was generated. Because envelopes vary with respect to their co-receptor usage, we included both CCR5 and CXCR4-specific envelopes. The panel of recombinant gp120 proteins was then exposed to primary PBMCs as well as macrophages. HIV envelope induced the expression of cytokines, chemokines, kinases, and transcription factors associated with antigen-specific T cell activation. Of note, these events occurred in the absence of cellular proliferation. It is possible that gp120-mediated effects increase the susceptibility of target cells to productive infection and contribute to the low level replication of HIV in cells that do not express markers of activation. Replication in this manner may contribute to the establishment and maintenance of reservoirs of HIV infection.? ? In agreement with the microarray data we demonstrated that HIV envelope induces the replication of HIV from resting CD4+ T cells of HIV-infected patients in the absence of induction of markers of classical T cell activation. These data suggest that HIV virions or free envelope protein induced a level of cellular stimulation that is sufficient for HIV replication, but that is below the threshold required for classic T cell activation. Furthermore, this model suggests that HIV may propagate itself in non-dividing cells that have an inherently longer half-life than do classically activated T cells. Because HIV viruses that utilize CXCR4 rather than CCR5 are associated with rapid disease progression we extended our analysis to compare and evaluate the differential effect of CCR5- vs. CXCR4-specific envelope proteins with respect to signal transduction and changes in cellular transcription. Interestingly, we found that genes associated with protein modification were differentially modulated by CCR5- vs. CXCR4-specific envelope proteins. This information may help us understand why CCR5-specific viruses are preferentially transmitted, and predominate early in disease, and why, in some individuals, CXCR4-specific envelopes predominate late in disease and are associated with increased the rates of disease progression. Answering these questions may aid us in designing better anti-HIV treatments and effective vaccines.
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