Thesis (Ph. D., Microbiology, Molecular Biology and Biochemistry)--University of Idaho, August 2008. / Major professor: Kurt E. Gustin. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 85-98). Available also in a digital version from Dissertation Abstracts.

Human ISG15 is a 17 kDa ubiquitin-like protein (Ubl) that is induced by type I interferons (interferons [alpha] and [beta]) and plays a role in antiviral responses. ISG15 is conjugated via its C-terminus to more than 150 cellular proteins, and like ubiquitin, an E1-E2-E3 enzymatic cascade is required for conjugation. Ube1L and UbcH8 were previously identified as the E1 and E2 enzymes for this pathway. My experiments identified Herc5, a HECT domain E3, as the major ligase for ISG15. Like ISG15, Ube1L, and UbcH8, expression of Herc5 is transcriptionally induced by type I interferons. siRNAs against Herc5 abrogated ISG15 conjugation to the vast majority of target proteins in interferon-treated cells. Wild type Herc5, but not the catalytically inactive C994A mutant, supported conjugation of ISG15 in non-interferon-treated cells co-transfected with Ube1L, UbcH8 and ISG15. IQGAP1, a scaffold protein, was identified as another essential component of the ISG15 system. IQGAP1 was discovered to interact with Herc5, and this interaction was mediated by the C-terminal domain of IQGAP1 and the N-terminal RCC1-like repeats of Herc5. IQGAP1 was required for auto-conjugation of ISG15 to Herc5, and I propose a model where IQGAP1 functions, at least in part, by relieving an auto-inhibitory conformation of Herc5. Thus, I have identified two factors that are critical for ISG15 conjugation and my discoveries have increased our understanding of the ISG15 pathway. Identification and characterization of the conjugation apparatus will aid in establishing an in vitro biochemical system for ISG15 conjugation, which in turn, will be important to decipher the biological function of ISG15 modification. / text

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The interferon (IFN) system is a powerful antiviral defense system. Host cell pattern recognition receptors (PRRs) recognise pathogen-associated molecule patterns (PAMPs) which when activated, lead to the transcription of the IFN-β gene. As a consequence IFN is secreted from the cell and activates the JAK-STAT pathway to up-regulate the transcription of IFN-stimulated genes (ISGs). The products of many ISGs inhibit viral replication and cell proliferation. Viruses encode IFN antagonists that dampen down the IFN response, making it less effective. However, within a virus population, there are always likely to be naturally occurring mutant viruses that have lost the ability to circumvent the host IFN response, and if isolated, these viruses would be unlikely to cause severe disease in the host and may therefore be developed as live attenuated virus vaccine candidates. To develop a methodology to rapidly isolate IFN-inducing mutant viruses, we generated an A549 reporter cell-line in which expression of GFP was driven by the IFN-β promoter. Using this cell-line, we show that the number of cells that became positive for GFP correlated with the amount of IFN secreted by the infected cells and the number of defective interfering (DI) particles within the virus preparations. However, we were unable to isolate IFN-inducing mutant viruses using the A549/pr(IFN-β).GFP cell-line(s). Possible reasons for this may be either that, in cells infected by IFN-inducing mutant viruses, an antiviral state was established independent of IFN that prevented virus replication in the reporter cells in which the IFN-β promoter was activated; or the viruses that activated the IFN-β promoter were DIs only which were not be able to replicate without non-defective helper viruses. A549/pr(IFN-β).GFP cells are also being used for high throughput assays to screen chemical libraries for compounds that block IFN induction. Such compounds may be potential candidates for anti-inflammatory drugs.

Abstract not available

Thesis (doctoral)--University of Uppsala, 1983. / Bibliography: p. 32-37.