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

Abstract

As an obligate intracellular pathogen, host cell invasion is paramount to Chlamydia trachomatis proliferation. While the mechanistic underpinnings of this essential process remain illdefined, 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.

TheChlamydia trachomatistype III effector TarP coordinates a functional collaboration between the actin nucleators Formin 1 and Arp2/3 during invasion

“…Given recent evidence demonstrating that the Chlamydia effector TmeA also activates Arp2/3 during invasion by signaling through N-WASP it is likely that the residual recruitment of actin and Arp2/3 in ΔTarP strains is due, at least in part, to the activity of TmeA (Fig. 5A) (41,42). A direct comparison between WT, ΔTarP, ΔTmeA, ΔTarP/ ΔTmeA strains with regards to dynamics of actin, Fmn1, and Arp2/3 at the invasion site would be required to assess accurately their relative contributions.…”

Got mutants? How advances in chlamydial genetics have furthered the study of effector proteins

“…Interactions between N-WASP and TmeA promote recruitment of the ARP2/3 complex to the invasion site, presumably driving actin branching events necessary for filopodia capture and internalization of EBs (Faris et al . 2020 ) (Fig. 3 ).…”

“…New research indicates that TmeA possesses a GTPase binding domain (GBD) ligand motif that binds to the NPF N-WASP (Faris et al . 2020 ). Interactions between N-WASP and TmeA promote recruitment of the ARP2/3 complex to the invasion site, presumably driving actin branching events necessary for filopodia capture and internalization of EBs (Faris et al .…”

“…While TmeA was shown to be necessary for N-WASP recruitment to the invading EB, the ARP2/3 complex was still recruited in the absence of TmeA and N-WASP, albeit to a significantly lower degree (Faris et al . 2020 ). This suggests that C. trachomatis employs multiple methods to recruit the ARP2/3 complex to the EB invasion site.…”

“…Indeed, a TarP mutant was similarly impaired in ARP2/3 recruitment, whereas recruitment to a TmeA/TarP double mutant was completely abolished (Faris et al . 2020 ). TarP was previously shown to bind Rac GEFs and it was hypothesized that this leads to activation of WAVE2 and the ARP2/3 complex (Carabeo et al .…”