Induction and Utilization of an ATM Signaling Pathway by Polyomavirus

Abstract

ABSTRACT Progression from G 1 to S is essential for polyomavirus DNA replication and depends on the interaction of large T with the retinoblastoma gene product pRb. This virus-induced replication pathway is accompanied by p53 activation resembling a DNA damage response (12). We sought to determine whether this pathway depends in part on activation of the ATM ( a taxia t elangiectasia m utated) kinase and whether the virus gains advantages from this pathway beyond that of entry into S. We show that polyomavirus infection activates the S- and G 2 -phase checkpoints in primary as well as established mouse cells. Infected cells undergo a prolonged S phase compared to uninfected serum-stimulated cells and show no evidence of a G 2 →M transition before lytic death ensues. Infection is accompanied by increases in ATM activity in vitro and in the level of ATM-S1981-P in vivo. The incubation of infected cells with caffeine, a known ATM inhibitor, did not block entry into S but reduced the rate of viral compared to cellular DNA synthesis. Importantly, caffeine lowered the yields of viral DNA an average of 3- to 6-fold and those of infectious virus by as much as 10-fold. Virus yields were 10-fold lower in ATM −/− p53 −/− than in ATM +/+ p53 −/− mouse embryo fibroblasts, indicating a p53-independent role of ATM in productive infection. Replacement of the normal SMC1 ( s tructural m aintenance of c hromosomes, or cohesin) protein, a critical ATM substrate in the DNA repair pathway, with its phosphorylation mutant SMC1 S957AS966A also lowered virus yields by roughly 90%. We suggest that polyomavirus activates and utilizes a component(s) of an ATM pathway of DNA repair to prolong S phase and aid its own replication.