CYRI1-mediated inhibition of RAC1 signalling restrictsSalmonellaTyphimurium infection

Abstract

Salmonella presents a global public health concern. Central to Salmonella pathogenicity is an ability to subvert host defence mechanisms through bacterial effectors that target key host proteins implicated in restricting infection. Thus, to gain insight into host-pathogen interactions governing Salmonella infection, a thorough understanding of host defence mechanisms is needed. To tackle this, we performed an in vivo genome-wide ENU mutagenesis screen to uncover novel host defence proteins. Through this screen we identified an uncharacterised protein, which we name CYRI1 (CYFIP-related RAC1 Interacting protein 1) that serves as a Salmonella resistance factor. We show that CYRI1 binds to the small GTPase RAC1 through a conserved domain present in CYFIP proteins, which are known RAC1 effectors that stimulate actin polymerisation. However, unlike CYFIP proteins, CYRI1 negatively regulates RAC1-driven actin cytoskeleton remodelling, thereby attenuating processes such as phagocytosis and cell migration. This, in turn, enables CYRI1 to counteract Salmonella at various stages of infection, including bacterial entry into epithelial cells, internalisation into myeloid-derived phagocytes as well as phagocyte-mediated bacterial dissemination. Together, this outlines a novel host defence mechanism that is crucial for determining bacterial fate.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/238733 doi: bioRxiv preprint first posted online Dec. 22, 2017; 3 Enteropathogenic bacteria are a major public health concern, accounting for over 300 million foodborne illnesses and 60 % of related fatalities worldwide. Among these bacteria, Salmonella enterica subspecies (subsp.) enterica serotypes are associated with the largest disease burden 1 . In fact, it is estimated that nontyphoidal Salmonella, alone, accounts for approximately 93.8 million illnesses and 155,000 deaths worldwide per year 2 . This, together with the increasingly widespread emergence of antibiotic-resistant Salmonella strains 3 , calls for a better understanding of the molecular mechanisms underlying Salmonella pathogenicity and the associated host cellular responses.Salmonella enterica subsp. are facultative, motile, Gram-negative bacteria that invade phagocytic M cells of the Peyer's patches (PP) as well as non-phagocytic enterocytes 4 . Upon breaching the gastrointestinal mucosa, Salmonella spread to the mesenteric lymph nodes (MLNs) and are engulfed by phagocytes, including macrophages, neutrophils and dendritic cells 5 . Depending on host-pathogen dynamics, phagocytes can provide a protective niche for bacterial replication 6 .Additionally, phagocyte migration can also aid dissemination to secondary tissues, such as the spleen and liver, where Salmonella can replicate further 4,6,7 .Underlying Salmonella pathogenicity is an ability to hijack host cel...

CYRI/ Fam49 Proteins Represent a New Class of Rac1 Interactors

“…This suggests a possible immune function for CYRI-B, possibly at the level of bacterial uptake, which requires engagement of the actin cytoskeletal machinery and Rac1 activation [34]. They further show in this study that CYRI-B can be destroyed by ubiquitination downstream of Rac1 activation by the Salmonella effector SopE, suggesting interesting possibilities for regulation of CYRI-B in cells [34].…”

“…CYRI-B interacts with active forms of Rac1, such as Rac1 P29S , Rac1 Q61L [15,34] and interestingly appears to show increased affinity to double mutant Rac1 P29S/Q61L [15]. Rac1 P29S/Q61L was first described by Chen and colleagues [3] but is not a naturally occurring mutation (to our knowledge).…”

“…It remains for the future to discover the mechanism by which CYRI may impact on superoxide production and whether this is related to Rac1 control of NOX or mitochondrial ROS production. Additionally, Yuki et al [34] report that CYRI-B restricts Salmonella infection in mice, as they identified CYRI in a screen for novel genes that when mutated affected susceptibility to infection. This suggests a possible immune function for CYRI-B, possibly at the level of bacterial uptake, which requires engagement of the actin cytoskeletal machinery and Rac1 activation [34].…”

“…Additionally, Yuki et al [34] report that CYRI-B restricts Salmonella infection in mice, as they identified CYRI in a screen for novel genes that when mutated affected susceptibility to infection. This suggests a possible immune function for CYRI-B, possibly at the level of bacterial uptake, which requires engagement of the actin cytoskeletal machinery and Rac1 activation [34]. They further show in this study that CYRI-B can be destroyed by ubiquitination downstream of Rac1 activation by the Salmonella effector SopE, suggesting interesting possibilities for regulation of CYRI-B in cells [34].…”