Abstract
Human cytomegalovirus (HCMV) is a ubiquitous pathogen capable of causing life threatening consequences in neonates and immune-compromised individuals. HCMV inflicts site-specific double strand breaks (DSBs) in the cellular genome. DNA damage infliction raises the corollary question of virus modulation of DNA repair. We recently reported HDR was stimulated in wt human foreskin fibroblasts (HFFs) during fully permissive infection or expression of the HCMV protein IE1-72 (IE72). These studies have been extended into semi-permissive T98G glioblastoma cells. T98Gs encode a mutant p53, which may contribute to their high baseline rate of HDR. We fully expected HCMV infection to increase HDR in T98Gs, similar to its effects in HFFs. Surprisingly in T98Gs HCMV infection, or sole expression of IE72, decreased HDR by two-fold. Transient expression of wt p53 in T98Gs also reduced HDR by two-fold. Dual transient expression of wt p53 and IE72 restored high baseline HDR levels. GST pulldown experiments revealed that both IE72 and wt p53 bound the important HDR protein, Rad51. We conclude that the expression of certain HCMV proteins can modulate HDR in an infected cell, dependent upon p53 status. We propose a model of the protein interactions explaining this behavior.
Highlights
Human cytomegalovirus (HCMV) is a member of the β-herpesvirus family and is endemic in the human population
Our earlier study assessed whether HCMV infection affected homology-directed repair (HDR) of an integrated substrate at
This work found that HDR, as measured by an increase in green fluorescent protein (GFP)+ cells, was stimulated in human foreskin fibroblasts (HFFs) during HCMV infection and, further, that expression of the HCMV protein IE72 on its own stimulated HDR [12]
Summary
Human cytomegalovirus (HCMV) is a member of the β-herpesvirus family and is endemic in the human population. HCMV can cause congenital birth defects, primarily of neurological origin [1,2,3]. One of the direct effects of HCMV infection in human foreskin fibroblasts (HFFs), is the induction of two site-specific breaks at chromosome 1q42 and 1q23.3 in the host cellular DNA [7,8]. DNA damage triggers a cascade of complex protein signaling pathways. In the case of double-stranded breaks (DSBs), two repair pathways are principally activated (as reviewed in [10,11]). HCMV infection caused a two-fold increase in HDR of an I-SceI induced site-specific DNA DSB, from a baseline level of 4% to a stimulated level of 8%. A model to explain the interaction of HCMV IE72 with p53 and the HDR machinery is proposed
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