Host Cell S Phase Restricts Intracellular Replication by Destabilizing the Membrane-Bound Replication Compartment.

grows within cells ranging from environmental amoebae to human macrophages. In spite of this conserved strategy of pathogenesis, identification of host factors that restrict intracellular replication has not been extended outside components of the mammalian innate immune response. We performed a double-stranded RNA (dsRNA) screen against more than 50% of the annotated open reading frames (ORFs) to identify host cell factors that restrict The majority of analyzed dsRNAs that stimulated intracellular replication were directed against host proteins involved in protein synthesis or cell cycle control. Consistent with disruption of the cell cycle stimulating intracellular replication, proteins involved in translation initiation also resulted in G arrest. Stimulation of replication was dependent on the stage of cell cycle arrest, as dsRNAs causing arrest during S phase had an inhibitory effect on intracellular replication. The inhibitory effects of S phase arrest could be recapitulated in a human cell line, indicating that cell cycle control of replication is evolutionarily conserved. Synchronized HeLa cell populations in S phase and challenged with failed to progress through the cell cycle and were depressed for supporting intracellular replication. Poor bacterial replication in S phase was associated with loss of the vacuole membrane barrier, resulting in exposure of bacteria to the cytosol and their eventual degradation. These results are consistent with the model that S phase is inhibitory for intracellular survival as a consequence of failure to maintain the integrity of the membrane surrounding intracellular bacteria. has the ability to replicate within human macrophages and amoebal hosts. Here, we report that the host cell cycle influences intracellular replication. Our data demonstrate that the G and G/M phases of the host cell cycle are permissive for bacterial replication, while S phase is toxic for the bacterium. replicates poorly within host cells present in S phase. The inability of to replicate relies on its failure to control the integrity of its vacuole, leading to cytosolic exposure of the bacteria and eventual degradation. The data presented here argue that growth-arrested host cells that are encountered by in either the environment or within human hosts are ideal targets for intracellular replication because their transit through S phase is blocked.