A Small-Scale shRNA Screen in Primary Mouse Macrophages Identifies a Role for the Rab GTPase Rab1b in Controlling Salmonella Typhi Growth

Acknowledgments We are very grateful to Leigh Knodler for her generous gift of P22 phages from a S. Typhimurium glmS::Cm::mCherry strain. We thank the Microscopy and Histology Core Facility, the Centre for Genome-Enabled Biology and Medicine (CGEBM), the Iain Fraser Cytometry Centre and the qPCR Facility (University of Aberdeen) for their support and assistance in this work. We thank members of the Spanò/Baldassarre laboratory for their feedback throughout this project. The content of this manuscript has been posted as a preprint on bioRxiv (Solano-Collado et al., 2020). Funding This work was supported by the European Union’s Horizon 2020 research and innovation program Marie Skłodowska-Curie Fellowship (706040_KILLINGTYPHI) to VS-C, the Wellcome Trust (Seed Award 109680/Z/15/Z), the European Union’s Horizon 2020 ERC consolidator award (2016-726152-TYPHI), the BBSRC (BB/N017854/1) and Tenovus Scotland (G14/19) to SS.Peer reviewedPublisher PD

The Rab32/BLOC-3-dependent pathway mediates host defense against different pathogens in human macrophages.

Macrophages provide a first line of defense against microorganisms, and while some mechanisms to kill pathogens such as the oxidative burst are well described, others are still undefined or unknown. Here, we report that the Rab32 guanosine triphosphatase and its guanine nucleotide exchange factor BLOC-3 (biogenesis of lysosome-related organelles complex-3) are central components of a trafficking pathway that controls both bacterial and fungal intracellular pathogens. This host-defense mechanism is active in both human and murine macrophages and is independent of well-known antimicrobial mechanisms such as the NADPH (reduced form of nicotinamide adenine dinucleotide phosphate)-dependent oxidative burst, production of nitric oxide, and antimicrobial peptides. To survive in human macrophages, Salmonella Typhi actively counteracts the Rab32/BLOC-3 pathway through its Salmonella pathogenicity island-1-encoded type III secretion system. These findings demonstrate that the Rab32/BLOC-3 pathway is a novel and universal host-defense pathway and protects mammalian species from various pathogens