Modulation of innate immune signalling by salmonella effector SteE
File(s)
Author(s)
Panagi, Ioanna
Type
Thesis
Abstract
During Salmonella infection, bacterial proteins called effectors are delivered inside host cells via dedicated proteinaceous apparatuses termed Type III Secretion Systems, which span the bacterial and host cell membranes. Delivered effectors modulate host cell signalling cascades and their actions dictate the phenotypic state of the infected cell. Recently, S. Typhimurium effector SteE was shown to shift macrophages – an important immune cell type – toward an anti-inflammatory and infection-permissive phenotype, by activating the host transcription factor STAT3. The mechanism underlying SteE-mediated STAT3 activation remained enigmatic but required the mammalian serine/threonine (S/T) kinases GSK3α and GSK3β. In this thesis, the molecular action of SteE is described. Specifically, translocated SteE is found to stably interact with GSK3α/β and the transcription factor STAT3, forming a complex wherein STAT3 is phosphorylated on Y705. STAT3 phosphorylation is shown to be catalysed by GSK3, but only in the presence of SteE, demonstrating that SteE alters the amino acid and substate specificity of this host kinase. Further work found that GSK3 stabilises SteE, within the infected cell and that GSK3 phosphorylates SteE before targeting STAT3, with mutational analysis identifying two key SteE phospho-residues required for function. The T91 residue of SteE stabilises the interaction to GSK3α/β whereas Y143 residue within a C-terminal, eukaryotic-like YxxQ motif is essential for STAT3 interaction, supporting a model whereby SteE mimics a eukaryotic motif to recruit STAT3 to GSK3. Work here additionally revealed that STAT1 is another substrate of the SteE-GSK3 complex and that STAT1 and STAT3 heterodimerise during Salmonella infection in an SteE-dependent manner, but the physiological relevance of these events remains unknown. Finally, transcriptomic profiling in infected 293ET cells, an epithelial-like cell line, ascertained that STAT3 governs most, if not all, SteE-driven transcriptional responses. Overall, this thesis provides in-depth insights on the mechanism of an effector that promotes bacterial pathogenesis.
Version
Open Access
Date Issued
2022-10-26
Date Awarded
01/03/2023
License URL
Advisor
Thurston, Teresa
Sponsor
Medical Research Council (Great Britain)
Biotechnology and Biological Sciences Research Council (Great Britain)
Grant Number
MR/N014103/1
BB/R011834/1
Publisher Department
Department of Infectious Disease
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)