EPEC adhere, and result in the local effacement in the microvilli of intestinal epithelial cells, providing raise to so referred to as attaching and effacing lesions. In vitro, EPEC attach to infected cells by forming pedestal like structures enriched in polymerized actin as well as other host cell proteins. The kind III secretion technique delivers into host cells the translocated intimin receptor, that is inserted into the cell plasma membrane such that a loop is exposed around the cell surface that binds to yet another bacterial protein, the adhesin intimin. This binding induces the clustering of Tir, followed by its phosphorylation on tyro sine residue 474 in the cytoplasmic C terminal domain. The phosphotyrosine moiety recruits the host cell adaptor protein Nck, which binds and presumably activates N WASP, leading to actin polymerization mediated by the Arp2 3 complex.
Even though this pathway is recognized because the principal one particular operating in EPEC, a further Nck inde find out this here pendent pathway has also been described in these bacteria. In addition, the complexity of EPEC signal transduc tion will not be completely understood. Tir is inserted in the cell membrane, where it adopts a hairpin loop structure, with both N and C termini project ing into the host cytoplasm. Pedestals are dynamic structures that undergo continuous remodeling by cycles of actin polymerization depolymerization. It can be impor tant to know the contribution of other signals to pedestal formation, not just for EPEC but also for other actin based processes. For example, it has been postulated that Tir Nck signaling mimics the nephrin Nck actin pathway.
Cortactin is a key regulator in the actin cytoskeleton which plays a essential part in cell invasion and actin based motility for the duration of the infection of quite a few microbial patho gens. Cortactin possesses an N terminal acidic domain which harbors a DDW motif that activates, selleck chemicals MK-2206 albeit weakly, the Arp2 3 complex at branching points. The NTA domain is followed by a series of repeat domains that bind filamentous actin. The C ter minal SH3 domain of cortactin binds a variety of pro teins, like N WASP, that is a ubiquitously expressed member from the WASP loved ones of proteins. Cortactin is usually phosphor ylated by tyrosine kinases and serine threonine kinases. Src kinase targets tyrosine residues 421, 466 and 482 although Erk phos phorylates serines 405 and 418 which lie within a proline rich area. Interestingly, a Src family members member and Abl kinases phosphorylate Tir. The Arp2 3 complicated may be independently activated to initiate actin polymerization by the VCA domain of WASP members and by both the NTA and F actin binding repeats of cortactin. Theoreti cally N WASP, cortactin as well as the Arp2 3 complicated can form ternary complexes.