The principal goal of this project is to understand the influence of HIV envelope-mediated signaling on viral replication and immune dysfunction. HIV envelope proteins, which are displayed on the surface of viral particles initially dock with the human T cell CD4 receptor, and subsequently engage either the CCR5 or CXCR4 co-receptor. Envelope binding to each of these receptors triggers a signal transduction cascade; however, the consequences of such signaling are only partially understood. In previous studies, we and others have demonstrated that HIV envelope-mediated signaling induces multiple biological responses in primary T-cells and macrophages including the induction and 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. Because HIV envelopes vary in their primary sequence, we developed a panel of envelopes representing each of the five major sub-types of HIV, including R5 and X4 envelopes, to better understand the effect of sequence variation on envelope signaling. Primary PBMCs were then treated with each of the recombinant gp120 proteins in the panel. HIV envelope induced the expression of genes encoding cytokines, chemokines, kinases, and transcription factors associated with antigen-specific T cell activation. Transcriptional changes that reflect permissiveness for HIV replication included an upregulation of genes encoding NFAT, induction of the RNA polymerase II complex (TFII D, e.g.), and expression of certain plasma membrane associated proteins (syntaxins and Rho proteins, including cdc42, e.g.). These transcriptional changes occurred in the absence of cellular proliferation. We hypothesize 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. Such low level replication may contribute to the establishment and maintenance of latent HIV reservoirs. In agreement with the microarray data, we subsequently demonstrated that HIV envelope induces the expression of HIV from resting CD4+ T cells of HIV-infected patients in the absence of induction of classical T cell activation markers. These data suggest that HIV virions or free envelope protein induce 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 compared the effects of R5 vs X4 envelope proteins on changes in cellular transcription. Interestingly, we found that genes associated with transcription, protein modification and cell cycle were differentially modulated by R5 vs X4 envelope proteins. This information may help explain why CCR5-specific viruses are preferentially transmitted and predominate early in disease, whereas CXCR4-specific envelopes predominate late in disease and are associated with increased rates of disease progression in some individuals. Answering these questions may help in the development of better anti-HIV treatments and more effective vaccines.
Showing the most recent 10 out of 19 publications
