Human cytomegalovirus UL76 induces chromosome aberrations

Abstract

BackgroundHuman cytomegalovirus (HCMV) is known to induce chromosome aberrations in infected cells, which can lead to congenital abnormalities in infected fetuses. HCMV UL76 belongs to a conserved protein family from herpesviruses. Some reported roles among UL76 family members include involvement in virulence determination, lytic replication, reactivation of latent virus, modulation of gene expression, induction of apoptosis, and perturbation of cell cycle progression, as well as potential nuclease activity. Previously, we have shown that stable expression of UL76 inhibits HCMV replication in glioblastoma cells.MethodsTo examine chromosomal integrity and the DNA damage signal γ-H2AX in cells constitutively expressing UL76, immunofluorescent cell staining and Western blotting were performed. The comet assay was employed to assess DNA breaks in cells transiently expressing UL76.ResultsWe report that stably transfected cells expressing UL76 developed chromosome aberrations including micronuclei and misaligned chromosomes, lagging and bridging. In mitotic cells expressing UL76, aberrant spindles were increased compared to control cells. However, cells with supernumerary centrosomes were marginally increased in UL76-expressing cells relative to control cells. We further demonstrated that UL76-expressing cells activated the DNA damage signal γ-H2AX and caused foci formation in nuclei. In addition, the number of cells with DNA breaks increased in proportion to UL76 protein levels.ConclusionOur findings suggest that the virus-associated protein UL76 induces DNA damage and the accumulation of chromosome aberrations.

Interferon, the Cell Cycle and Herpesvirus

“…The precise mechanism of cell cycle arrest induced by UL24 homologues remains to be clarified. An interesting and possible explanation is the recent report that HCMV UL76 induces chromosomal aberrations and DNA damage (Siew et al, 2009). Phosphorylation of ATM and -H2AX, accepted signals of DNA damage activation, were also observed for HSV-1 UL24 (our unpublished work), possibly revealing a conserved effect similar to the observed cell cycle arrest.…”

“…Phosphorylation of ATM and -H2AX, accepted signals of DNA damage activation, were also observed for HSV-1 UL24 (our unpublished work), possibly revealing a conserved effect similar to the observed cell cycle arrest. It may be relevant that the number of cells with DNA damage breaks increased with increasing levels of the UL76 protein, a feature perhaps related to the putative endonuclease activity of the viral protein (Siew et al, 2009). Another example of this multi-functionality of virus host evasion proteins is the induction of the expression of interleukin-8 (IL-8) by the HCMV UL76 gene (our unpublished work).…”

Promotion of Tumorigenesis and Clinical Implications of Viral Infection in Breast Cancer

“…Previous studies have shown expression of HCMV-UL76 is not restricted to lytic replication and HCMV-UL76 can be detected in latently infected hematopoietic CD34+ cells and stable expression of HCMV-UL76 in glioblastoma cells inhibits viral replication in these cells [104,105]. Persistent expression of HCMV-UL76 in the cells and inhibition of viral replication leads to accumulation of multiple chromosome aberrations, chromosome misalignments, and increased formation of micronuclei containing activated DNA damage signal γ-H2AX [102].…”

“…HCMV-UL76 protein can induce DNA damage, apoptosis, cell cycle arrest [102] and inhibition of DNA repair machinery [103]. Previous studies have shown expression of HCMV-UL76 is not restricted to lytic replication and HCMV-UL76 can be detected in latently infected hematopoietic CD34+ cells and stable expression of HCMV-UL76 in glioblastoma cells inhibits viral replication in these cells [104,105].…”

Viral and cellular subnuclear structures in human cytomegalovirus-infected cells

“…Although endonuclease activity of UL76 has yet to be demonstrated, indirect evidence points to a role for UL76 in the chromosome breakage required for chromatin partitioning. For example, the presence of UL76 in uninfected cells is sufficient to stimulate chromosomal aberrations (Siew et al, 2009), and in HCMV-infected cells, UL76 is involved in stimulating a DNA damage response (Costa et al, 2013).…”