Herpesviruses show consistency in their nuclear egress-associated induction of lamina-depleted areas as measured in an autofluorescent reporter cell model

Abstract Human herpesvirus infections span a wide variety of pathogenic outcomes, with individual representatives comprising a huge clinical relevance on human health. Translational research efforts are directed towards the improvement of broadly applicable preventive measures and detailed understanding of viral pathogenesis. Here, we studied rate-limiting steps in viral replication that show high mechanistic conservation among the Herpesviridae family members, in particular concerning the viral nucleocytoplasmic capsid egress. As characterized for several herpesviruses, viral nuclear egress is facilitated by the virus-induced local nuclear lamina rearrangements of infected cells. Hereby, the virus-mediated site-specific phosphorylation at lamin A/C Ser22, followed by cis/trans isomerization of the structural conformation, leads to the induction of lamina-depleted areas (LDAs). We have generated an LDA reporter system in primary human fibroblasts (HFFs), which conditionally express the autofluorescent lamin A/C-RFP fusion construct, for quantifying viral nuclear egress activity. This system was successfully applied for human and animal cytomegaloviruses as well as a selection of α-, β-, and γ-herpesviruses shown here. Our results illustrate that (i) the reporter system was effective in a quantitative way for all viruses analyzed; (ii) the process of LDA formation showed consistency among herpesviruses; (iii) the impairment of viral kinase activity, responsible for lamin A/C Ser22 phosphorylation, significantly reduced LDA formation; and (iv) inhibitory small molecules, directed either to the viral nuclear egress complex or the cellular isomerase activity, likewise provide an LDA-blocking effect leading to strong antiviral efficacy. Thus, the autofluorescent reporter cell model provides manifold options to study herpesviral productive replication, nuclear host interaction, and the pathogenesis-related impact of regulatory factors.