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.

Loss of the Birt–Hogg–Dubé gene product folliculin induces longevity in a hypoxia‐inducible factor–dependent manner

“…hif-1-dependent upregulation of lys-7 is essential for increased thermotolerance of the flcn-1-mutant strain over WTN2, providing a possible regulator downstream of hif-1. Moreover -because lys-7 encodes an antimicrobial lysozyme -this finding provides another putative link between hif-1 and the defense against bacterial pathogens (Shao et al, 2010;Luhachack et al, 2012). Yet, the question whether hif-1 is an essential mediator of longevity in flcn-1-mutant worms or whether the mere presence of hif-1 is required for this phenotype cannot be finally answered.…”

Impaired expression of hypoxia-inducible factor-1α in cystic fibrosis airway epithelial cells – A role for HIF-1 in the pathophysiology of CF?

“…By driving expression of genes involved in host immunity and inflammation, studies with HIF-1α knockout mice revealed that activation of HIF-1 after pathogen interaction (Group A Streptococcus, Yersinia enteroletica or P. aeruginosa) is essential for a full inflammatory response in the host (15)(16)(17). However, as we know, CF-affected cells have imbalanced inflammatory responses during infection.…”

Feedback regulation via AMPK and HIF-1 mediates ROS-dependent longevity in Caenorhabditis elegans

“…The physiological importance of HIF-1α in humans is underscored by the fact that mutations in VHL, the von HippelLindau tumor suppressor gene, which encodes an E3-ubiquitin ligase component required for the degradation of HIF-1, lead to an inherited form of cancer (18,19). HIF-1 regulates adaptation to low oxygen and various other biological processes, including axon guidance, immunity, iron homeostasis, and aging (20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Increased levels of HIF-1 by vhl-1 mutations or by overexpression of HIF-1 lengthen the lifespan of C. elegans (27,28).…”