Competitive interplay between xenophagy and viral evasion mechanisms of autophagy during human cytomegalovirus infection

• Applicant: Christine Zimmermann, Ph.D.
• Subject Area: Virology ; Cell Biology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433733331

Xenophagy, a form of selective autophagy, is a cellular defense mechanism that restricts the replication of invading pathogens. Infection with viruses and other intracellular agents leads to the induction of the autophagy cascade that ultimately may result in the lysosomal degradation of the pathogen. Many viruses however, have developed mechanisms to evade autophagosomal degradation. Herpesviruses in particular have been shown to utilize various strategies to manipulate autophagy even to their own benefit. There is increasing evidence that virus-host interactions with regard to autophagy are far more complex than previously thought and that there is a competitive and intricate interplay between pro- and antiviral mechanisms that ultimately determines the success of viral replication. This project addresses the regulation of autophagy in the course of human cytomegalovirus (HCMV) infection, with a particular focus on the viral mechanisms that lead to evasion of antiviral autophagy. Conflicting results have been published regarding the interference of HCMV with the autophagy machinery, indicating either pro- or antiviral effects. We could confirm the induction of autophagy after HCMV infection by showing a considerable increase of the membrane-bound form of the ubiquitin-like protein LC3, a protein that is conjugated to membrane lipids of the nascent autophagosome. Using an HCMV mutant expressing a dominant-negative version of the protease ATG4B, thereby inhibiting autophagy, we found a marked increase of viral replication and release. Concordant with this, we found evidence that immature HCMV virions were targeted for autophagosomal degradation in wtHCMV-infected cells. In contrast, both lipidated LC3 and autophagy receptors were also detected in extracellular viral particles, indicating that autophagic membranes were involved in envelopment. These results suggest that there are competing pro- and antiviral processes in HCMV infected cells. Work in this project focuses on addressing the mechanisms underlying these competing processes. It is known that the specific selection and degradation of cargo is mediated by autophagy receptors, which recognize both the cargo and LC3. The specificity of these receptors is closely regulated via posttranslational modifications. In particular, phosphorylation on certain residues has been shown to determine receptor affinity for specific types of cargo. The proposed work is based on the hypothesis that the selectivity of particular autophagy receptors for different viral components is a critical determinant that regulates the degradation of capsids versus viral envelopment and release. This project aims at understanding the role of particular autophagy receptors for HCMV replication and elucidating the importance of phosphorylation of these receptors in the regulation of viral cargo selection.

• DFG Programme: Research Grants