UC Berkeley

Viruses have evolved to manipulate the cellular environment to promote their replication and spread. They do so by encoding viral effectors that co-opt or disrupt cellular processes to create an environment suitable for infection. This dissertation will discuss two viral proteins that disrupt cellular homeostasis. First, I will present work demonstrating that the SARS-CoV-2 Envelope (E) protein interferes with retention of the endoplasmic reticulum (ER) aminopeptidase associated with antigen processing (ERAAP) in cells. To protect the SARS-CoV-2 fusion protein Spike from improper cleavage by Golgi resident proteases, E protein increases the pH of this compartment. The change in pH delays trafficking and likely impairs the function of these proteases. We show that E-mediated Golgi pH neutralization impedes ERAAP retention likely by disrupting the interaction between ERAAP and ERp44, a chaperone we and others have shown to control ERAAP localization. Specifically, we demonstrate that the expression of SARS-CoV-2 E results in decreased ERAAP intracellular levels and ERAAP secretion into the extracellular environment. ERAAP’s reliance on ERp44 and a functioning ER/Golgi pH gradient for proper localization and function led us to propose that ERAAP serves as a sensor of disturbances in the secretory pathway during infection and disease.

The second viral protein that will be discussed is the M18 protein from murine cytomegalovirus (MCMV). Previous work found that M18 disrupts the function of histone deacetylases (HDACs). HDACs are epigenetic modulators capable of controlling gene expression by removing acetyl modifications on histones and non-histone proteins. Importantly, HDACs have been shown to regulate herpesvirus replication and latency. Moreover, herpesviruses encode proteins that antagonize or harness the action of these enzymes. I aimed to elucidate the cellular functions of M18 and the contribution of this protein to viral pathogenesis. Here, we demonstrate that M18 is produced as two isoforms, M18L and M18S, during infection. These isoforms likely possess different functions, as suggested by their differential localization. Furthermore, using RNAseq, we found that M18 regulates the expression of a subset of immune-related genes, including various members of the chemokine family. We hypothesize that induction of these factors by M18 could promote viral dissemination by recruiting monocytes, which are known MCMV reservoirs.

Altogether, this dissertation presents work that expands our understanding of viral effectors and their cellular functions. These contributions further illuminate the complex interactions between viruses and their hosts.