Person:

Kirienko, Natalia

The nematode Caenorhabditis elegans offers currently untapped potential for carrying out high-throughput, live-animal screens of low molecular weight compound libraries to identify molecules that target a variety of cellular processes. We previously used a bacterial infection assay in C. elegans to identify 119 compounds that affect host-microbe interactions among 37,214 tested. Here we show that one of these small molecules, RPW-24, protects C. elegans from bacterial infection by stimulating the host immune response of the nematode. Using transcriptome profiling, epistasis pathway analyses with C. elegans mutants, and an RNAi screen, we show that RPW-24 promotes resistance to Pseudomonas aeruginosa infection by inducing the transcription of a remarkably small number of C. elegans genes ((\sim)1.3% of all genes) in a manner that partially depends on the evolutionarily-conserved p38 MAP kinase pathway and the transcription factor ATF-7. These data show that the immunostimulatory activity of RPW-24 is required for its efficacy and define a novel C. elegans–based strategy to identify compounds with activity against antibiotic-resistant bacterial pathogens.

Organisms are constantly challenged by stresses and privations and require adaptive responses for their survival. The transcription factor DAF-16/FOXO is central nexus in these responses, but despite its importance little is known about how it regulates its target genes. Proteomic identification of DAF-16/FOXO binding partners in Caenorhabditis elegans and their subsequent functional evaluation by RNA interference (RNAi) revealed several candidate DAF-16/FOXO cofactors, most notably the chromatin remodeller SWI/SNF. DAF-16/FOXO and SWI/SNF form a complex and globally colocalize at DAF-16/FOXO target promoters. We show that specifically for gene-activation, DAF-16/FOXO depends on SWI/SNF, facilitating SWI/SNF recruitment to target promoters, in order to activate transcription by presumed remodelling of local chromatin. For the animal, this translates into an essential role of SWI/SNF for DAF-16/FOXO-mediated processes, i.e. dauer formation, stress resistance, and the promotion of longevity. Thus we give insight into the mechanisms of DAF-16/FOXO-mediated transcriptional regulation and establish a critical link between ATP-dependent chromatin remodelling and lifespan regulation.

Metazoans identify and eliminate bacterial pathogens in microbe-rich environments such as the intestinal lumen, however the mechanisms are unclear. Potentially, host cells employ intracellular surveillance or stress response programs to detect pathogens that target monitored cellular activities to initiate innate immune responses1–3. Mitochondrial function is evaluated by monitoring mitochondrial protein import efficiency of the transcription factor ATFS-1, which mediates the mitochondrial unfolded protein response (UPRmt). During mitochondrial stress, import is impaired4 allowing ATFS-1 to traffic to the nucleus where it mediates a transcriptional response to re-establish mitochondrial homeostasis5. Here, we examined the role of ATFS-1 during pathogen exposure because in addition to mitochondrial protective genes, ATFS-1 induced innate immune genes during mitochondrial stress that included a secreted lysozyme and anti-microbial peptides. Exposure to the pathogen Pseudomonas aeruginosa caused mitochondrial dysfunction and activation of the UPRmt. Animals lacking atfs-1 were susceptible to P. aeruginosa, while hyper-activation of ATFS-1 and the UPRmt improved clearance of P. aeruginosa from the intestine and prolonged C. elegans survival largely independent of known innate immune pathways6,7. We propose that ATFS-1 import efficiency and the UPRmt is a means to detect pathogens that target mitochondria and initiate a protective innate immune response.