Inactivation of checkpoint kinase 1 (Chk1) during parvovirus minute virus of mice (MVM) infection inhibits cellular homologous recombination repair and facilitates viral genome replication

During infection, the autonomous parvovirus minute virus of mice (MVM) induces cellular DNA breaks and localizes to such sites, which presumably affords an environment beneficial for genome replication. MVM replication also benefits from the DNA damage response (DDR) mediated by the ataxia-telangiectasia mutated (ATM) kinase, while the ataxia telangiectasia and Rad-3 related (ATR) arm of the DDR is disabled, which prevents activation of its primary target, checkpoint kinase 1 (Chk1). We find here that Chk1 inactivation strongly correlates with dephosphorylation of one of its targets, RAD51, known to play a pivotal role in homologous recombination repair (HRR), thus leading to substantial inhibition of DNA repair in infected cells. We demonstrate colocalization of replicating MVM DNA with cellular double-strand breaks (DSBs) during infection, and show that an agent that exogenously induces cellular DSBs significantly increases viral DNA replication levels, establishing a role for cellular genome damage in facilitating virus DNA replication. Additionally, overexpression of active Chk1 during MVM infection was found to re-establish the activating phosphorylation of RAD51 Thr 309, significantly suppress infection-induced reduction of HRR efficiency with a concomitant increase in cellular genome DSBs, and reduce viral DNA replication levels. Thus, we conclude that during infection, MVM inhibition of Chk1 activation enhances viral replication, at least in part, by inhibiting cellular HRR.IMPORTANCEThe autonomous parvovirus minute virus of mice (MVM) has a compact DNA genome encoding a minimum number of proteins. During infection, it induces cellular DNA damage and both utilizes and modifies the subsequent cellular DNA damage response (DDR) in various ways to facilitate its replication. One of MVM's activities in this regard is to inhibit one of the primary arms of the DDR, the ataxia telangiectasia and Rad-3 related (ATR) pathway, which prevents activation of checkpoint kinase 1 (Chk1), a key protein involved in controlling the cellular DDR and preserving genome integrity. We show that prevention by MVM of Chk1 activation leads to inhibition of homologous recombination repair (HRR) of cellular DNA, which helps sustain viral replication. This work illuminates another way in which autonomous parvoviruses adjust the cellular environment for their replicative advantage.