Britt Glaunsinger

The ability to regulate RNA stability has the potential to impact gene expression on a global scale, but is also critical for fine-tuning cellular responses to specific stimuli as well as eliminating flawed and potentially deleterious transcripts. Lytic gammaherpesvirus infection promotes widespread destruction of messenger RNAs (mRNAs), a phenotype driven primarily by the viral endonuclease SOX. By probing how SOX and other functionally related viral proteins drive messenger RNA degradation, we hope to reveal novel interplay between viruses and host gene regulatory pathways, as well as identify cellular factors with capacity to broadly influence message stability. We are also probing how cells sense and respond to broad changes in RNA levels, such as those induced by viral infection.

Roles for Virus-Induced RNA Turnover in Pathogenesis

Many viruses are known to restrict host gene expression via a variety of different mechanisms. While proposed to facilitate immune evasion and to aid in the reallocation of cellular resources towards viral replication, in very few cases has the role of this specific phenotype during in vivo infection of a host been directly evaluated. We are using a close relative of KSHV, murine gammaherpesvirus 68 (MHV68), to examine the role of mRNA degradation in the in vivo replication and pathogenesis of gammaherpesviruses.

Although the vast majority of messages are degraded during lytic KSHV infection, we know that some transcripts escape degradation and accumulate robustly. Prominent among these is human interleukin 6 (IL-6), a B cell growth factor that has been demonstrated to play a role in the pathogenesis of several KSHV-associated neoplasms. By creating chimeric mRNAs, we have identified a specific element within IL-6 that renders it directly refractory to degradation by SOX. We are in the process of identifying how factors that bind this element directly influence its susceptibility to SOX-induced cleavage.

Identification of Novel Translation Strategies Used by KSHV

Viruses do not encode translation machinery and thus operate under the constraints of host protein synthesis. However, the compact nature of viral genomes has resulted in the evolution of specialized strategies to maximize their coding capacity. The KSHV genome, for example, contains a many fewer poly(A) sites than genes, often with a single signal allocated for several consecutive open reading frames (ORFs). In many cases alternative splicing or gene-specific promoters allow production of nested sets of transcripts, enabling most KSHV ORFs to be positioned as the 5’ gene for normal cap-dependent translation. However, there exist some genes that appear to be translated as downstream genes from polycistronic mRNAs. We are currently exploring noncanonical mechanisms that enable such genes to be efficiently recognized by the host translation machinery.

Systems Biology of the Virus-Host Interaction

Many of the proteins encoded by large DNA viruses like KHSV are of unknown function. We are applying systems level proteomics approaches to define the complex set of host factors associated with each viral protein. This should enable both the assignment of specific functions to each viral factor, as well as reveal the composite of host signaling networks and pathways targeted by the virus during infection. We are currently using these data to probe new mechanisms by which herpesvirues commandeer host gene expression machinery.