C. elegans swan-1 binds to egl-9 and regulates hif-1- mediated resistance to the bacterial pathogen pseudomonas aeruginosa pao1

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. © 2010 shao et al.