The purine nucleoside phosphorylase pnp-1 regulates epithelial cell resistance to infection in C. elegans

Abstract

Intestinal epithelial cells are subject to attack by a diverse array of microbes, including intracellular as well as extracellular pathogens. While defense in epithelial cells can be triggered by pattern recognition receptor-mediated detection of microbe-associated molecular patterns, there is much to be learned about how they sense infection via perturbations of host physiology, which often occur during infection. A recently described host defense response in the nematode C. elegans called the Intracellular Pathogen Response (IPR) can be triggered by infection with diverse natural intracellular pathogens, as well as by perturbations to protein homeostasis. From a forward genetic screen, we identified the C. elegans ortholog of purine nucleoside phosphorylase pnp-1 as a negative regulator of IPR gene expression, as well as a negative regulator of genes induced by extracellular pathogens. Accordingly, pnp-1 mutants have resistance to both intracellular and extracellular pathogens. Metabolomics analysis indicates that C. elegans pnp-1 likely has enzymatic activity similar to its human ortholog, serving to convert purine nucleosides into free bases. Classic genetic studies have shown how mutations in human purine nucleoside phosphorylase cause immunodeficiency due to T-cell dysfunction. Here we show that C. elegans pnp-1 acts in intestinal epithelial cells to regulate defense. Altogether, these results indicate that perturbations in purine metabolism are likely monitored as a cue to promote defense against epithelial infection in the nematode C. elegans.

The transcription factor ZIP-1 promotes resistance to intracellular infection in Caenorhabditis elegans

“…Indeed, we found a more pronounced role for zip-1 after viral infection of pnp-1 mutants, which have constitutive expression of IPR genes, including pals-5 (Fig. 6b ) 15 . Of note, our qRT-PCR analysis of pnp-1(jy90) animals showed that elevated pals-5 mRNA levels depend on zip-1 , suggesting that the IPR genes upregulated by zip-1 promote resistance against viral infection (Supplementary Fig.…”

“…Therefore, zip-1 is required for induction of pals-5 p::GFP expression after infection by these two natural intracellular pathogens of the C. elegans intestine. We next tested if zip-1 was required for constitutive expression of pals-5 p::GFP in pnp-1 mutants 15 . Here, we also saw a requirement for zip-1 , as zip-1(jy13); pnp-1(jy90) double mutants had much less pals-5 p::GFP signal compared to pnp-1 single mutants (Fig.…”

“…Other phenotypes in pnp-1 mutants include higher sensitivity to heat shock and slightly slower growth rate 15 . We tested if either of these phenotypes are zip-1 -dependent.…”

“…While intracellular infection by the Orsay virus or by N. parisii cause hallmarks of proteotoxic stress in C. elegans intestinal cells 11 , genetic and kinetic analyses indicate that proteotoxic stress is activating IPR gene expression in parallel to viral infection, and that there are several independent triggers of the IPR 10 . Another trigger of the IPR is mutation in the enzyme purine nucleoside phosphorylase-1, PNP-1, which acts in C. elegans intestinal epithelial cells to regulate pathogen resistance and the majority of IPR genes 12 , 13 , 15 . Of note, mutations in human PNP cause T-cell dysfunction, but its role in epithelial cells is less well-described 15 .…”

“…Another trigger of the IPR is mutation in the enzyme purine nucleoside phosphorylase-1, PNP-1, which acts in C. elegans intestinal epithelial cells to regulate pathogen resistance and the majority of IPR genes 12 , 13 , 15 . Of note, mutations in human PNP cause T-cell dysfunction, but its role in epithelial cells is less well-described 15 . In addition to pnp-1 , analysis of another IPR repressor called pals-22 , has provided insight into the regulation and function of IPR genes 12 , 13 .…”