A Novel Mechanism Inducing Genome Instability in Kaposi's Sarcoma-Associated Herpesvirus Infected Cells

Abstract

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic herpesvirus associated with multiple AIDS-related malignancies. Like other herpesviruses, KSHV has a biphasic life cycle and both the lytic and latent phases are required for tumorigenesis. Evidence suggests that KSHV lytic replication can cause genome instability in KSHV-infected cells, although no mechanism has thus far been described. A surprising link has recently been suggested between mRNA export, genome instability and cancer development. Notably, aberrations in the cellular transcription and export complex (hTREX) proteins have been identified in high-grade tumours and these defects contribute to genome instability. We have previously shown that the lytically expressed KSHV ORF57 protein interacts with the complete hTREX complex; therefore, we investigated the possible intriguing link between ORF57, hTREX and KSHV-induced genome instability. Herein, we show that lytically active KSHV infected cells induce a DNA damage response and, importantly, we demonstrate directly that this is due to DNA strand breaks. Furthermore, we show that sequestration of the hTREX complex by the KSHV ORF57 protein leads to this double strand break response and significant DNA damage. Moreover, we describe a novel mechanism showing that the genetic instability observed is a consequence of R-loop formation. Importantly, the link between hTREX sequestration and DNA damage may be a common feature in herpesvirus infection, as a similar phenotype was observed with the herpes simplex virus 1 (HSV-1) ICP27 protein. Our data provide a model of R-loop induced DNA damage in KSHV infected cells and describes a novel system for studying genome instability caused by aberrant hTREX.

Murine Gammaherpesvirus 68 LANA and SOX Homologs Counteract ATM-Driven p53 Activity during Lytic Viral Replication

“…EBV induces a DDR during ZTA-driven reactivation, evidenced by ATM activation and phosphorylation of downstream targets (23). KSHV reactivation following inducible RTA expression similarly promotes enhanced H2AX phosphorylation (45) as well as the activation of a full DDR (63). Tarakanova and colleagues previously demonstrated that MHV68 infection of primary macrophages also induces ATM and H2AX phosphorylation (20), and we likewise observed the phosphorylation of H2AX and other ATM targets in a global phosphoproteomic analysis of MHV68 lytic infection (22).…”

“…MHV68 induces ATM and H2AX phosphorylation, and infected cells exhibit additional DDR-related phosphorylation events during lytic replication in fibroblasts (20,22,(43)(44)(45). However, the kinetics of the MHV68-associated DDR and whether it is associated with p53 activation are not well defined.…”

Stability of Structured Kaposi's Sarcoma-Associated Herpesvirus ORF57 Protein Is Regulated by Protein Phosphorylation and Homodimerization

“…Whether ORF57 directly promotes KSHV genome instability in infected cells (13) remains to be confirmed. Although all ORF57 functions involve ORF57 association with an RNA target, this association also requires cellular proteins to function as ORF57 cofactors (14,15), and each of the ORF57-specific functions depends on a specific cofactor(s).…”

Interplay between Kaposi's sarcoma-associated herpesvirus and the innate immune system

“…Analogously, a DDR-dependent effect involving APOBEC3G increases NKG2D ligand expression on HIV-infected primary T cells, resulting in enhanced NK cell-mediated lysis [97]. KSHV-mediated upregulation of the DDR has been reported in several other contexts [98-100], suggesting this pathway may be particularly important for NK cell recognition of KSHV-infected cells. On the other hand, NK cell ligand surface expression on fibroblasts latently infected with KSHV is not obviously altered compared to uninfected cells, suggesting MICA, MICB, ULBP2 upregulation may be a cell-type specific phenotype [92].…”