Avian sarcoma and leukosis viral entry mechanism and its inhibition by small molecules

Avian Sarcoma and Leukosis Viruses (ASLVs) are used as a retroviral model system to study mechanisms of envelope-receptor interactions, virus-cell membrane fusion, viral endocytosis, and intracellular virus-cell interactions. Studies of ASLV may lead to an improved understanding of HIV pathogenesis and the use of retroviruses as vectors for targeted gene therapy.;This dissertation describes studies in three major areas: Identification of the functional determinants in TVB, the receptor for ASLV subgroup B; the mechanism of cell binding and internalization when ASLV infection is mediated by a soluble receptor; and the identification of small molecule inhibitors of early steps of ASLV infection through high throughput screening.;A linear peptide encompassing amino acids 32--46 of TVB was shown to bind to subgroup B Env and was able to act as a minimal retroviral receptor that enabled viruses loaded with the peptide to infect receptor-negative cells. Key residues for the function of TVB32--46 were identified, and TVB32--46-mediated ASLV-B infection was shown to be absolutely dependent on a low pH intracellular environment, akin to ASLV infection mediated by membrane anchored receptors.;ASLV-B binding to cell surfaces was shown to be enhanced by the presence of TVB32--46, and heparan sulfate proteoglycans were shown to play an important role in soluble receptor peptide-mediated infection, which occurs with very slow kinetics through a pathway that was independent of clathrin-mediated endocytosis. These studies, combined with those undertaken by others, have revealed that ASLV can infect cells through distinct internalization pathways.;Finally, a library of small molecules was screened for inhibitors of early steps of ASLV entry in order to characterize cell factors required for ASLV entry, and for the potential development of novel antiretroviral agents. Several lead compounds were identified that inhibit both ASLV and HIV at multiple early steps in the entry lifecycle. Together, these studies have shed light on ASLV Env-receptor interactions and several aspects of the cell biology of ASLV infection.