title: C. elegans SWAN-1 Binds to EGL-9 and regulates HIF-1-mediated resistance to the bacterial pathogen Pseudomonas aeruginosa PAO1.
abstract: Pseudomonas aeruginosa is a nearly ubiquitous human pathogen, and infections can be lethal to patients with impaired respiratory and immune systems. Prior studies have established that strong loss-of-function mutations in the egl-9 gene protect the nematode C. elegans from P. aeruginosa PAO1 fast killing. EGL-9 inhibits the HIF-1 transcription factor via two pathways. First, EGL-9 is the enzyme that targets HIF-1 for oxygen-dependent degradation via the VHL-1 E3 ligase. Second, EGL-9 inhibits HIF-1-mediated gene expression through a VHL-1-independent mechanism. Here, we show that a loss-of-function mutation in hif-1 suppresses P. aeruginosa PAO1 resistance in egl-9 mutants. Importantly, we find stabilization of HIF-1 protein is not sufficient to protect C. elegans from P. aeruginosa PAO1 fast killing. However, mutations that inhibit both EGL-9 pathways result in higher levels of HIF-1 activity and confer resistance to the pathogen. Using forward genetic screens, we identify additional mutations that confer resistance to P. aeruginosa. In genetic backgrounds that stabilize C. elegans HIF-1 protein, loss-of-function mutations in swan-1 increase the expression of hypoxia response genes and protect C. elegans from P. aeruginosa fast killing. SWAN-1 is an evolutionarily conserved WD-repeat protein belonging to the AN11 family. Yeast two-hybrid and co-immunoprecipitation assays show that EGL-9 forms a complex with SWAN-1. Additionally, we present genetic evidence that the DYRK kinase MBK-1 acts downstream of SWAN-1 to promote HIF-1-mediated transcription and to increase resistance to P. aeruginosa. These data support a model in which SWAN-1, MBK-1 and EGL-9 regulate HIF-1 transcriptional activity and modulate resistance to P. aeruginosa PAO1 fast killing.
authors.affiliation: Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Shao
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Qi
authors.initials: Q
authors.lastname: Ye
authors.forename: Jenifer Neeta
authors.initials: JN
authors.lastname: Saldanha
authors.forename: Jo Anne
authors.initials: JA
authors.lastname: Powell-Coffman
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D015870:Gene Expression; D005786:Gene Expression Regulation; D015151:Immunoblotting; D047468:Immunoprecipitation; D009154:Mutation; D011552:Pseudomonas Infections / Q000276:immunology*; D011550:Pseudomonas aeruginosa / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029742:Caenorhabditis elegans Proteins; C403074:Egl-9 protein, C elegans; C541178:HIF-1 protein, C elegans; D014157:Transcription Factors