HOST-MEDIATED ALTERATION OF MEASLES VIRUS POLYMERASE ACTIVITY: CONSEQUENCES FOR THE OUTCOME OF INFECTION
Measles Virus (MeV) has a negative-sense, single-stranded RNA genome that is encapsidated by the viral nucleocapsid (N) protein. This ribonucleoprotein complex (RNP) forms the template for virus transcription and genome replication. The virus encoded RNA-dependent RNA polymerase (RdRp) complex is composed of the monomeric viral large (L) protein and the tetrameric polymerase co-factor (P) protein. Interaction between the RNP and the RdRp depends on transient contacts between P and the C-terminus of the N protein (NTAIL). Cyclic binding and release between P and N allow the polymerase complex to advance along the RNP template. The critical factor that should thus determine the rate of polymerase elongation, either during transcription or replication, is the binding affinity between N and P. This work addresses host-cell related factors that alter this affinity and thus influence the outcome of infection. Chapter 1 of this work describes how hsp72, the highly-inducible member of the 70-kDa heat shock protein family, along with other heat shock proteins, are expressed in the central nervous system and how these protein chaperones act to maintain cellular homeostasis, protect cells from insult, and preserve the specialized function of nervous tissue (i.e., to initiate and propagate the electrical impulses that dictate the actions of the rest of the body). These same heat shock proteins can also enhance the gene expression of neurotropic viruses (like MeV), and yet that stimulation of viral gene expression can enhance viral clearance by overcoming the host-restricted low levels of viral gene expression that otherwise confound adaptive antiviral immune responses. Thus, the stimulatory effect of hsp72 on viral gene expression remains consistent with its host protective functions ?uro;?uro;? provided that the host is immune competent. Chapter 2 focuses on the role of hsp72 on MeV gene expression, specifically its ability to alter the activity of the viral polymerase, either during transcription or genome replication, or both. Using a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) approach to monitor the kinetics of MeV transcription and genome replication, it was determined that the effect of hsp72 is to maintain nucleocapsid in a transcriptionally competent state during the late stages of infection. Chapter 3 describes a possible mechanism by which post-translational modification of Box-3 may alter the outcome of MeV infection in ways that mimic hsp72/Box-3 interaction. Here, the effect of tyrosine phosphorylation within NTAIL on polymerase activity and infection phenotype is examined. Information in this chapter provides a link between tyrosine phosphorylation and altered polymerase activity that is capable of promoting a persistent infection state. Finally, chapter 4 describes an examination of the contribution of co-chaperone molecules to the high binding affinity between hsp72 and NTAIL. Binding studies in this work show that HSP40 co-chaperones are necessary for the well-described high affinity binding between hsp72 and NTAIL, making these co-chaperones an additional host factor capable of modulating viral gene expression. Collectively, these studies delineate some of the effects that intracellular host-factors have on MeV infection. These findings help clarify the complex interactions that gives rise to the diverse outcomes of MeV infection.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:measles virus hsp72 hsp40 nucleocapsid tyrosine phosphorylation
Date of Publication:01/01/2008