Cross Talk between ARF1 and RhoA Coordinates the Formation of Cytoskeletal Scaffolds during Chlamydia Infection.

Chlamydia trachomatis is an obligate intracellular bacterium that has developed sophisticated mechanisms to survive inside its infectious compartment, the inclusion. Notably, Chlamydia weaves an extensive network of microtubules (MTs) and actin filaments to enable interactions with host organelles and enhance its stability. Despite the global health and economic burden caused by this sexually transmitted pathogen, little is known about how actin and MT scaffolds are integrated into an increasingly complex virulence system. Previously, we established that the chlamydial effector InaC interacts with ARF1 to stabilize MTs. We now demonstrate that InaC regulates RhoA to control actin scaffolds. InaC relies on cross talk between ARF1 and RhoA to coordinate MTs and actin, where the presence of RhoA downregulates stable MT scaffolds and ARF1 activation inhibits actin scaffolds. Understanding how Chlamydia hijacks complex networks will help elucidate how this clinically significant pathogen parasitizes its host and reveal novel cellular signaling pathways. IMPORTANCE Chlamydia trachomatis is a major cause of human disease worldwide. The ability of Chlamydia to establish infection and cause disease depends on the maintenance of its parasitic niche, called the inclusion. To accomplish this feat, Chlamydia reorganizes host actin and microtubules around the inclusion membrane. How Chlamydia orchestrates these complex processes, however, is largely unknown. Here, we discovered that the chlamydial effector InaC activates Ras homolog family member A (RhoA) to control the formation of actin scaffolds around the inclusion, an event that is critical for inclusion stability. Furthermore, InaC directs the kinetics of actin and posttranslationally modified microtubule scaffolds by mediating cross talk between the GTPases that control these cytoskeletal elements, RhoA and ADP-ribosylation factor 1 (ARF1). The precise timing of these events is essential for the maintenance of the inclusion. Overall, this study provides the first evidence of ARF1-RhoA-mediated cross talk by a bacterial pathogen to coopt the host cytoskeleton.