The Chlamydia trachomatis secreted effector TmeA hijacks the N-WASP-ARP2/3 actin remodeling axis to facilitate cellular invasion

Author summary Chlamydia trachomatisis the etiological agent of trachoma and is the most common bacterial sexually transmitted infection worldwide. As an obligate intracellular pathogen, bacterial proliferation only occurs within the confines of a host cell, thus invasion is the critical step in the infection process. While the secreted effector protein TmeA is known to be essential for invasion and bacterial pathogenesis, how TmeA promotes invasion was previously unknown. Here we show that TmeA binds to the GTPase binding domain of the nucleation promoting factor N-WASP and their interaction is necessary for recruitment of the ARP2/3 complex to the bacterial entry foci. Moreover, our study shows that while the secreted effector protein TarP is also involved in recruiting the ARP2/3 complex, it functions in a pathway that is distinct from N-WASP. Collectively, our study suggests that TmeA and TarP target distinct cell signaling pathways that converge on the ARP2/3 complex, a key regulator of pathogen uptake. As an obligate intracellular pathogen, host cell invasion is paramount toChlamydia trachomatisproliferation. While the mechanistic underpinnings of this essential process remain ill-defined, it is predicted to involve delivery of prepackaged effector proteins into the host cell that trigger plasma membrane remodeling and cytoskeletal reorganization. The secreted effector proteins TmeA and TarP, have risen to prominence as putative key regulators of cellular invasion and bacterial pathogenesis. Although several studies have begun to unravel molecular details underlying the putative function of TarP, the physiological function of TmeA during host cell invasion is unknown. Here, we show that TmeA employs molecular mimicry to bind to the GTPase binding domain of N-WASP, which results in recruitment of the actin branching ARP2/3 complex to the site of chlamydial entry. Electron microscopy revealed that TmeA mutants are deficient in filopodia capture, suggesting that TmeA/N-WASP interactions ultimately modulate host cell plasma membrane remodeling events necessary for chlamydial entry. Importantly, while both TmeA and TarP are necessary for effective host cell invasion, we show that these effectors target distinct pathways that ultimately converge on activation of the ARP2/3 complex. In line with this observation, we show that a double mutant suffers from a severe entry defect nearly identical to that observed when ARP3 is chemically inhibited or knocked down. Collectively, our study highlights both TmeA and TarP as essential regulators of chlamydial invasion that modulate the ARP2/3 complex through distinct signaling platforms, resulting in plasma membrane remodeling events that are essential for pathogen uptake.