Borst, E. M. | bioRxiv Science

bioRxiv2025

Chromosome-associated spot formation by human cytomegalovirus immediate early 1 (IE1) protein

HCMV is associated with severe disease in immunocompromised patients and is a cause of congenital disease. Already more than 30 years ago, IE1 was described to bind to mitotic chromosomes, however the implications of this finding have yet to be determined. HCMV can infect a wide range of cell types and was also detected in different tumours; however, the majority of molecular studies relating to this virus are performed in fibroblasts or monocytic cells. We examined the localization of HCMV IE1 across multiple cell types, including tumour cell lines, to better understand how the protein behaves in these cellular contexts. IE1 is one of the first HCMV genes expressed after lytic infection of the cell and it was observed to distribute evenly over the chromosomes in so-called "chromosome painting" pattern. In leukemia and glioblastoma cells we detected a novel mitotic localization pattern of IE1 - in chromosome-associated spots (CAS), in addition to "painting the chromosomes", as reported before. We demonstrate that the IE1 core domain mediates CAS localization and that the distribution pattern of IE1 on mitotic chromosomes is influenced by both the cell type being infected and the level of IE1 expression. The novel CAS localization of IE1 suggests a new, possibly cell-type specific function of this protein, distinct from its role in transcriptional regulation.

microbiology↗

bioRxiv2019

Human cytomegalovirus nuclear capsid motility is non-directed and independent of nuclear actin bundles

Herpesvirus genome replication, capsid assembly and packaging take place in the host cell nucleus. Matured capsids leave the nucleus through a unique envelopment-de-envelopment process at the nuclear membranes called nuclear egress. How assembled and DNA-containing herpesvirus capsids reach the sites of nuclear egress is however still controversially discussed, as host chromatin that marginalizes during infection might constitute a major barrier. For alphaherpesviruses, previous work has suggested that nuclear capsids use active transport mediated by nuclear filamentous actin (F-actin). However, direct evidence for nuclear capsid motility on nuclear F-actin was missing. Our subsequent work did not detect nuclear F-actin associated with motile capsids, but instead found evidence for chromatin remodeling to facilitate passive capsid diffusion. A recent report described that human cyto-megalovirus, a betaherpesvirus, induces nuclear F-actin and that the motor protein myosin V localizes to these structures. Direct evidence of capsid recruitment to these structures and motility on them was however missing. In this study, we tested the functional role of HCMV-induced, nuclear actin assemblies for capsid transport. We did not observe transport events along nuclear F-actin. Instead, reproduction of nuclear F-actin was only possible using strong overexpression of the fluorescent marker LifeAct-mCherry-NLS. Also, two alternative fluo-rescent F-actin markers did not detect F-actin in HCMV-infected cells. Furthermore, single particle tracking of nuclear HCMV capsids showed no indication for active transport, which is in line with previous work on alphaherpesviruses.

microbiology↗