Chlamydial Entry Involves TARP Binding of Guanine Nucleotide Exchange Factors

Abstract

Chlamydia trachomatis attachment to cells induces the secretion of the elementary body–associated protein TARP (Translocated Actin Recruiting Protein). TARP crosses the plasma membrane where it is immediately phosphorylated at tyrosine residues by unknown host kinases. The Rac GTPase is also activated, resulting in WAVE2 and Arp2/3-dependent recruitment of actin to the sites of chlamydia attachment. We show that TARP participates directly in chlamydial invasion activating the Rac-dependent signaling cascade to recruit actin. TARP functions by binding two distinct Rac guanine nucleotide exchange factors (GEFs), Sos1 and Vav2, in a phosphotyrosine-dependent manner. The tyrosine phosphorylation profile of the sequence YEPISTENIYESI within TARP, as well as the transient activation of the phosphatidylinositol 3-kinase (PI3-K), appears to determine which GEF is utilized to activate Rac. The first and second tyrosine residues, when phosphorylated, are utilized by the Sos1/Abi1/Eps8 and Vav2, respectively, with the latter requiring the lipid phosphatidylinositol 3,4,5-triphosphate. Depletion of these critical signaling molecules by siRNA resulted in inhibition of chlamydial invasion to varying degrees, owing to a possible functional redundancy of the two pathways. Collectively, these data implicate TARP in signaling to the actin cytoskeleton remodeling machinery, demonstrating a mechanism by which C. trachomatis invades non-phagocytic cells.

Chlamydial Intracellular Survival Strategies

“…At least one early secreted effector, TARP, contributes to bacterial internalization by its ability to directly nucleate actin polymerization through a WH2 actin-binding domain mimic (Jewett et al 2006) and by recruiting the guanine nucleotide exchange factors (GEFs) Sos1 and Vav2, which activate Rac1 and signal to the actin machinery (Carabeo et al 2007;Lane et al 2008). This latter mechanism is only relevant in chlamydial species inwhich the polymorphic TARP gene (Clifton et al 2005) can be targeted for tyrosine phosphorylation by Abl, Src, and Syk kinases (Elwell et al 2008;Jewett et al 2008;Lane et al 2008;Mehlitz et al 2008Mehlitz et al , 2010. Microinjection of cells with antibodies directed to the actin-binding domain of TARP before infection significantly reduces bacterial invasion, providing the most conclusive support for a direct role of TARP in mediating bacterial entry (Jewett et al 2010).…”

Rho GTPases as pathogen targets: Focus on curable sexually transmitted infections

“…29 This phosphorylation allows TARP to recruit the GEFs Sos1 and Vav2, which in turn activate Rac1. 35 Subsequently, Rac1 recruits WAVE2 and Abl interactor 1 (Abi-1), leading to actin-related protein (Arp2/3) complex activation and actin recruitment and polymerization at the bacterial binding site. 36 It has been proposed that a synergistic action between both bacterial and host cell proteins promotes invasion.…”

Identification and biochemical characterization of the CHLAMYDIA TRACHOMATIS type III secretion chaperone, SLC1, and its role in the translocation of the invasion-associated effector TARP.

“…Translocation of effectors by a type III apparatus is a major strategy for Chlamydia entry, inclusion formation, and survival in eukaryotic cells [46,84,85]. Recruitment of host kinases and actin, in addition to activation ofRac and actin-poylmerization aid in endocytosis, and are functions attributed to the type III invasion associated effector TARP [42,66,67,69,132]. Chlamydia trachomatis urogenital, lymphogranuloma, and ocular strains synthesize T ARP homologs that contain three functional domains: tyrosine-rich repeats for recruitment of host kinases and subsequent Rac activation, a proline-rich aggregating domain, and actin-nucleating WH2-like domains.…”

“…Tyrosine phosphorylated residues in C trachomatis T ARP are able to recruit the guanine nucleotide exchange factors Sos-I and Vav-2 [67,68]. A complex ofSos-I, Eps8, and Abi-I or Vav-2 with PIP3 (phospho-inositoI3,4,5-P 3 ) have been shown to activate Rae in a phosphotyrosine dependent manner [67].…”

“…A complex ofSos-I, Eps8, and Abi-I or Vav-2 with PIP3 (phospho-inositoI3,4,5-P 3 ) have been shown to activate Rae in a phosphotyrosine dependent manner [67]. Rae-dependent recruitment of actin has been shown to involve Abi-I and WAVE-2 dependent formation of the actinnucleating Arp 2/3 complex [69].…”