Table of Contents

Previous and Current Research

The parvoviral (PV) protein NS2 is needed for assembly of the structural proteins into infectious particles in a cell-type-specific manner. It also appears to play a role in the generation and/or encapsidation of the PV genome and in modulating the cytotoxic activities of the major regulatory protein NS1. Yet the molecular mechanisms underlying NS2 activities are still unclear. To characterise them is our main research objective.
PV NS2 proteins associate with two members of the 14-3-3 protein family. Although the 14-3-3 proteins appear to play a role in NS2 phosphorylation, the NS2-14-3-3 complex is required neither for production of infectious particles nor for lysis of infected cells. PV NS2 proteins also associate with the nuclear export receptor Crm1 via a nuclear export signal, and are actively exported out of the nucleus of infected cells via a Crm1-dependent pathway. The NS2-Crm1 complex is required neither for synthesis of viral proteins nor for production of infectious virions, yet when NS2 export from the nucleus is abolished and/or the cytoplasm of infected cells is depleted of NS2, infectious PV particles are retained inside the nucleus. This correlates with prolonged survival of the infected cell population. We conclude that the PV protein NS2 is required for egress of progeny virions from the nucleus. Our data further suggest that PV NS2 proteins play a critical role at late steps of the PV replication cycle.

Future Projects and Goals

We will continue to evaluate how NS2 functions in PV-infected transformed cells. Three objectives will be considered.
- Functional analysis of NS2 in relation to the egress of progeny virions from the nucleus. The release of fully infectious particles is linked to (i) the synthesis of NS2 proteins and (ii) the phosphorylation status of the capsid proteins. Our aim is to determine how NS2 proteins affect the phosphorylation status of the capsid proteins.
- Functional analysis of NS2 in relation to PV cytopathogenicity. The parvoviral NS2 protein has been shown to attenuate PV-induced cell killing in certain cell lines. Our aim is to identify NS2 determinants responsible for the attenuation of PV-induced cell death. This study is supported by the “German-Israeli Foundation”.
- Functional analysis of NS2 in relation to human cancer cells. Our team has observed that a series of tumour cells are unable to produce progeny virions. Our aim is to evaluate the activity of NS2 in such cell lines and to determine which steps of the PV cycle are impaired.

The use of PV-based vectors in anticancer therapy is under investigation in our Inserm Unit. As the relatively low production rate of recombinant PV limits their applicability in clinical trials, our long-term goal is to understand the molecular mechanisms underlying the production of progeny PV and hence to improve this production.