Virus-host interactions during nuclear egress of parvoviruses

Abstract

Autonomic parvoviruses, small non-enveloped ssDNA viruses, encode only a limited number of proteins, which makes them highly dependent on the functions provided by the host cell. Besides two capsid proteins, VP1 and VP2, which form the capsid, autonomous parvoviruses encode two nonstructural proteins, NS1 and NS2. In this thesis, we used canine parvovirus as a model virus to study nuclear virus-host interactions and egress of progeny virus at late stages of infection. The NS1 of canine parvovirus has been identified to take part in multiple functions in infection, but the role of the smaller nonstructural protein NS2 has remained an enigma. In the first part of the study, we utilized proximity-dependent biotin identification (BioID), a powerful mass spectrometry-based tool capable of recognizing dynamic and transient interactions, to elucidate the role of NS2 in infection. The interactome linked NS2 to multiple proteins with possible relevance to the progression of infection. Notably, some gene ontology functions that were represented among the identified proteins were chromatin remodeling and DNA damage response, suggesting a regulatory involvement of NS2 in these processes. Moreover, the resolved BioID analysis revealed NS2 association with nucleolar proteins. In the second part of the study, we studied the nucleolar structure by deploying confocal imaging combined with human-in-the-loop (HITL) machine learning segmentation. Our findings show that nucleolar structure is changed during infection and intact NS2 has a role in these alterations. In the third part of the study, we showed that in addition to active CRM1-driven nuclear exit, the nuclear egress of capsids is facilitated by G2/M transition- and apoptosis-induced increase in the nuclear envelope permeability.