Phosphorylation of the Conserved Transcription Factor ATF-7 by PMK-1 p38 MAPK Regulates Innate Immunity in Caenorhabditis elegans

Abstract

Innate immunity in Caenorhabditis elegans requires a conserved PMK-1 p38 mitogen-activated protein kinase (MAPK) pathway that regulates the basal and pathogen-induced expression of immune effectors. The mechanisms by which PMK-1 p38 MAPK regulates the transcriptional activation of the C. elegans immune response have not been identified. Furthermore, in mammalian systems the genetic analysis of physiological targets of p38 MAPK in immunity has been limited. Here, we show that C. elegans ATF-7, a member of the conserved cyclic AMP–responsive element binding (CREB)/activating transcription factor (ATF) family of basic-region leucine zipper (bZIP) transcription factors and an ortholog of mammalian ATF2/ATF7, has a pivotal role in the regulation of PMK-1–mediated innate immunity. Genetic analysis of loss-of-function alleles and a gain-of-function allele of atf-7, combined with expression analysis of PMK-1–regulated genes and biochemical characterization of the interaction between ATF-7 and PMK-1, suggest that ATF-7 functions as a repressor of PMK-1–regulated genes that undergoes a switch to an activator upon phosphorylation by PMK-1. Whereas loss-of-function mutations in atf-7 can restore basal expression of PMK-1–regulated genes observed in the pmk-1 null mutant, the induction of PMK-1–regulated genes by pathogenic Pseudomonas aeruginosa PA14 is abrogated. The switching modes of ATF-7 activity, from repressor to activator in response to activated PMK-1 p38 MAPK, are reminiscent of the mechanism of regulation mediated by the corresponding ancestral Sko1p and Hog1p proteins in the yeast response to osmotic stress. Our data point to the regulation of the ATF2/ATF7/CREB5 family of transcriptional regulators by p38 MAPK as an ancient conserved mechanism for the control of innate immunity in metazoans, and suggest that ATF2/ATF7 may function in a similar manner in the regulation of mammalian innate immunity.

Caenorhabditis elegans microRNAs of the let-7 family act in innate immune response circuits and confer robust developmental timing against pathogen stress

“…***P < 0.001; two-tailed t test. regulation on pmk-1/p38-mediated gene expression (34). More intriguingly, the atf-7(gk715) allele enhances the phenotypes of the let-7-Fam miRNA mutant even more than the atf-7 null allele does, and the phenotype is suppressed when animals were exposed to P. aeruginosa (Fig.…”

Regulation of Anoxic Death in Caenorhabditis elegans by Mammalian Apoptosis Signal-Regulating Kinase (ASK) Family Proteins

“…Recently, the transcription factor ATF-7 has been reported to be regulated by the NSY-1-SEK-1-PMK-1 pathway in the context of innate immunity (Shivers et al 2010). If some of the pathogen-induced genes regulated by ATF-7 are also induced by anoxia, the mechanisms by which animals respond to pathogenic bacteria and anoxia would be at least partly the same.…”

Caenorhabditis elegans Immune Conditioning with the Probiotic Bacterium Lactobacillus acidophilus Strain NCFM Enhances Gram-Positive Immune Responses

“…The plates were incubated at 37°C for 18 h and cooled at room temperature (RT) for 1 h (P. aeruginosa for 24 h). For the solid killing assay, 10 l of E. faecalis cultures was spotted in the middle of BHI agar plates (35 mm) including 80 g/ml kanamycin, incubated at 37°C for 18 h, and cooled at room temperature for 1 h before beginning the experiment (35). For S. aureus (12), overnight cultures diluted 1:5 in fresh TSB were seeded on TSA plates (35 mm).…”

“…elegans killing assays. Liquid and solid killing assays were performed using published methods, with slight modifications (5,35). For the liquid killing assay, L4/young adult worms were placed on conditioning plates with L. acidophilus NCFM at 25°C for 24 h. After exposure to NCFM for 24 h, worms were moved onto lawns of the pathogen and plates were incubated at 25°C for 5 h. Of note is that, as expected, there were no E. coli HB101 bacteria present in the C. elegans gut after they were moved onto an NCFM conditioning plate (data not shown).…”