DNA SENSING ACTIVITY AND VIRAL INHIBITION OF HUMAN NUCLEAR DNA SENSORS

Abstract

Human cells are protected by cell-intrinsic mechanisms that specifically detect microbial pathogens and elicit innate immune response. Such activities are essential in restricting viral infections. Despite the extensive knowledge about cytoplasmic sensing processes, little is understood about the nuclear counterpart. In this thesis, this poorly understood immune response to nuclear viral DNA is studied from two perspectives--host antiviral defense and viral immune evasion.

In Chapter I, an overview to current understandings of cell-intrinsic immune response to foreign nucleic acids is first summarized. An important protein family, PYHIN proteins, is then introduced for their emerging roles in detecting intracellular viral DNA. Finally, I briefly describe a powerful technology, mass spectrometry-based proteomics, in studying host and pathogen interactions.

In Chapter II, I describe experiments that mechanistically investigated the role of one PYHIN protein, the interferon inducible protein IFI16, in detecting nuclear viral DNA and eliciting interferon response. The results demonstrate IFI16 as the first known nuclear DNA sensor, and identify acetylation within its conserved nuclear localization signal as a novel molecular toggle that regulates the sensing ability of IFI16.

In Chapter III, I show strong evidence that the major tegument protein pUL83 of human cytomegalovirus (HCMV) blocks IFI16-mediated nuclear DNA sensing. The results establish that the pUL83-IFI16 interaction critically determines the immunological outcome of HCMV infections in human cells, and showcase an intricate interplay between host and a viral pathogen.

In Chapter IV, I explore the role of another PYHIN protein, IFIX, as a novel DNA sensor. Evidence is described to show that IFIX has a similar function with IFI16.

In Chapter V, a new mass spectrometer, MALDI-LTQ-Orbitrap XL is functionally assessed for characterizing isolated protein complexes, a technique frequently utilized in the above chapters, highlighting useful applications of proteomics in studying host and virus interactions.