Transient inhibition of poly(ADP-ribose) polymerase expression and activity by Toxoplasma gondii is dispensable for parasite-mediated blockade of host cell apoptosis and intracellular parasite replication

Poly(ADP-ribose) polymerase-1 (PARP-1; EC 2.4.2.30) is an abundant nuclear protein that is involved in DNA repair, cell cycle control, programmed cell death and transcriptional regulation. It also plays critical roles in the pathogenesis of inflammatory disorders. Here we have performed a detailed analysis of the interplay between the apicomplexan parasite Toxoplasma gondii and host cell PARP and its consequences for the host-parasite relationship. Our results have shown that T. gondii significantly decreased PARP expression in its host cells within 10 min of infection but that the amount of PARP normalized during prolonged infection. Importantly, down-regulation of PARP expression after infection abrogated the ADP-ribosylation of acceptor proteins in response to oxidative stress. Overexpression of PARP in RAW264.7 cells revealed that elevated amounts of PARP neither affected host cell invasion nor intracellular development of T. gondii in non-stimulated or IFN-γ/LPS-stimulated monocytes/macrophages. Furthermore, measurements of the activities of effector caspases 3 and 7 indicated that the blockade of host cell apoptosis by T. gondii occurs independently of the inhibition of PARP after infection. These findings suggest that the prominent decrease of host cell PARP and poly(ADP-ribos)ylation after parasitic infection do not affect the intracellular development of T. gondii in vitro.