The principal objective of this project is to characterize the consequences of signal transduction mediated by HIV and/or its products as they relate to HIV replication and immune dysfunction. HIV envelope proteins bind to and signal through the CD4 receptor and also through CCR5 and CXCR4. These receptors are expressed on subsets of T-cells and macrophages. As a consequence of signaling, HIV envelope induces a number of biological responses in primary T-cells and macrophages including the induction of expression of proinflammatory cytokines and increased rates of apoptosis. Elucidation of the complexities and significance of the signaling processes that HIV-1 envelope induce may substantially enhance our understanding of HIV-1 pathogenesis. A major goal of this project is to understand the influence that envelope-mediated signaling has on viral replication and immune dysfunction. This information will hopefully facilitate the discovery of new strategies for the treatment of HIV infection. To obtain a more complete picture of the effect of envelope on the function and metabolic state of peripheral blood mononuclear cells (PBMCs), an experimental strategy was developed in which PBMCs from healthy donors were exposed to HIV envelope, and changes in the transcriptional program were determined using high-density oligonucleotide microarrays. Because envelopes vary with respect to their co-receptor usage and tropism, a panel of recombinant envelopes that encompass those viral phenotypes ascribed to the envelope was generated. This panel included both CCR5 and CXCR4-specific envelopes. Envelopes representing each of the five major sub-types of HIV were generated, as well as SIV envelopes. We employed those recombinant gp120 proteins to treat 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. Transcriptional changes that were observed included an upregulation of NFAT, induction of the RNA polymerase II complex including TFII D and certain plasma membrane associated proteins including several syntaxins, and members of the Rho protein family including Cdc 42. 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 expression of HIV from resting CD4+ T cells of HIV-infected patients in the absence of induction of markers of classical T cell activation. Recombinant trimeric HIV envelope protein induced the expression of HIV from resting (CD25-CD69-HLA-DR-, non-dividing) CD4+ T cells isolated from HIV-infected individuals. Envelope protein from both R5 and X4 HIV strains induced replication competent HIV. These data suggest that HIV virions or free envelope protein induced a level of cellular stimulation that is sufficient for HIV expression, 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. This analysis was extended further to determine the differential effect of CCR5- vs. CXCR4-specific envelope proteins. Interestingly, among the significant findings obtained from this analysis was the observation that genes associated with protein modification were differentially modulated by CCR5- vs. CXCR4-specific envelope proteins. This information may help us in understanding 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 increase the rate of disease progression. Answering these questions may aid us in designing better anti-HIV treatments and effective vaccines.
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