One candidate upstream component is the leucine-rich repeat (LRR)-containing G-protein-coupled receptor (GPCR) follicle-stimulating hormone receptor (FSHR-1), which was identified in a limited reverse see more genetic screen of 14 candidate transmembrane LRR receptors in C. elegans. RNAi directed against fshr-1 results in a high degree of susceptibility to killing by P. aeruginosa, Staphylococcus aureus and Enterococcus faecalis, but not in a reduced lifespan during infection by non-pathogenic E. coli[24]. Expression of FSHR-1 in intestinal cells is necessary and sufficient for its role in innate immunity. Genetic analysis
indicates that FSHR-1 functions in the intestine in a separate pathway from PMK-1 and DAF-2, the worm insulin receptor that is involved in stress responses (see below) [24]. Further, qRT–PCR analysis shows that FSHR-1 and the PMK-1/p38 MAPK cassette regulate the induction of overlapping, but non-identical, sets of P. aeruginosa-induced genes. Although transcriptional profiling data suggest that FSHR-1 regulates host response genes independently of PMK-1, it is unclear whether the PMK-1/p38 MAPK cassette may be involved partially in signal transduction downstream of FSHR-1 [24].
It is also possible that the FSHR-1 and PMK-1/p38 MAPK pathways function O-methylated flavonoid in parallel but converge on common sets of target genes in response to pathogen infection. How is FSHR-1 involved in mediating the C. elegans host response? Daporinad We currently lack evidence that FSHR-1 can sense infection directly, for instance by binding pathogen-associated molecular patterns (PAMPs). FSHR-1 is the sole C. elegans LGR-type
GPCR. In mammals the heterodimeric glycopeptide hormone FSHα/β is the canonical ligand for this class of GPCR. Worms do not have an identifiable FSHα subunit and the endogenous ligands, if any, have not been identified. As an LGR-type receptor, one might expect FSHR-1 to transduce signals through heterotrimeric G-proteins in the intestinal cell. Recent findings implicate at least one heterotrimeric G-protein in signal transduction events upstream of PMK-1 in a different tissue, the hypodermis (see below). Whether this or other G-proteins mediate FSHR-1 signal transduction in the intestine remains unknown. Recent findings show that the protein kinase Cδ (PKCδ) TPA-1 activates the protein kinase D DKF-2 upstream of PMK-1/p38 in the intestine [20]. The upstream signals that control TPA-1 activity remain unknown, although by analogy with other systems, a likely candidate is diacylglycerol (DAG, produced by phospholipase C).