| Despite over 25 years of research there are no effective vaccines against or cures for Human Immunodeficiency Virus Type 1 (HIV) infection. Further, potential anti-viral targets remain unidentified, as we have a limited understanding of the host proteins which contribute to productive HIV infection. Elucidation of these host factors, particularly in the primary cells targeted by HIV, their viral interaction partners and their precise mechanism of action will provide HIV researchers and clinicians with new anti-viral targets.;All of the predominant cell types infected by HIV, activated CD4+T cells, macrophages, and dendritic cells express the class II transactivator (CIITA). However, the role of CIITA and its transcriptional target HLA-DR in the HIV infection cycle are largely unstudied or provide conflicting results. Here we demonstrate that CIITA may play a more significant role during HIV infection than previously thought, based on studies using various CIITA-expressing cell lines and primary CD4+ T cells. In Chapter I we demonstrate that CIITA expression in CD4+ T cells enhances virion binding, infection kinetics, and cell death. Interestingly this effect appears to be independent of all known CIITA-mediated transcription products, but is dependent upon the gp120-CD4 interaction Chapter II reveals a novel cytoplasmic function for CIITA. This work revealed that CIITA-mediated enhancement of ribosomal frameshifting in the cytoplasm leads to increased HIV protease production and thus increased virion maturation and viral infectivity. Finally, Chapter III describes initial studies examining the mechanism by which HLA-DR is incorporated into the envelope of budding virions, specifically the role of enhanced ubiquitination of HLA-DR we observed in HIV-infected cells. In this chapter we demonstrate that ubiquitination of HLA-DR is by an indirect mechanism and independent of the cytoplasmic tail residues of the HLA-DR heterodimer, which are dispensable for viral -HLA-DR incorporation. Further, we detected an as-yet-unidentified 20kDa potential interaction partner of HLA-DR, which may be responsible for the indirect ubiquitination of HLA-DR in HIV infected cells and may play a role in viral budding.;These studies are the first to thoroughly assess the role of CIITA and HLA-DR during the complete HIV infection cycle using multiple cell types. Further, this work not only identifies a novel, cytoplasmic functional site for a well known nuclear transactivator, but also reveals specific points in the HIV cycle upon which CIITA acts to enhance the HIV virus replication cycle. Thus we have identified potential new targets for anti-viral therapies, and set the stage for further research to identify the molecular mechanisms by which CIITA influences HIV replication. Subsequent studies may ultimately provide better a understanding as to why activated cells are more susceptible to HIV infection, and allow for the development of more effective vaccine modalities, microbicides and anti-virals. |
