Functional divergence of dafachronic acid pathways in the control of C. elegans development and lifespan

Abstract

Steroid hormone and insulin/insulin-like growth factor signaling (IIS) pathways control development and lifespan in the nematode Caenorhabditis elegans by regulating the activity of the nuclear receptor DAF-12 and the FoxO transcription factor DAF-16, respectively. The DAF-12 ligands Δ4- and Δ7-dafachronic acid (DA) promote bypass of the dauer diapause and proper gonadal migration during larval development; in adults, DAs influence lifespan. Whether Δ4- and Δ7-DA have unique biological functions is not known. We identified the 3-β-hydroxysteroid dehydrogenase (3βHSD) family member HSD-1, which participates in Δ4-DA biosynthesis, as an inhibitor of DAF-16/FoxO activity. Whereas IIS promotes the cytoplasmic sequestration of DAF-16/FoxO, HSD-1 inhibits nuclear DAF-16/FoxO activity without affecting DAF-16/FoxO subcellular localization. Thus, HSD-1 and IIS inhibit DAF-16/FoxO activity via distinct and complementary mechanisms. In adults, HSD-1 was required for full lifespan extension in IIS mutants, indicating that HSD-1 interactions with IIS are context-dependent. In contrast to the Δ7-DA biosynthetic enzyme DAF-36, HSD-1 is dispensable for proper gonadal migration and lifespan extension induced by germline ablation. These findings provide insights into the molecular interface between DA and IIS pathways and suggest that Δ4- and Δ7-DA pathways have unique as well as overlapping biological functions in the control of development and lifespan.

Unexpected Role for Dosage Compensation in the Control of Dauer Arrest, Insulin-Like Signaling, and FoxO Transcription Factor Activity inCaenorhabditis elegans

“…To test this model, we determined the effect of dpy-21 RNAi on the subcellular localization of a functional DAF-16A::GFP fusion protein (Henderson and Johnson 2001b) in daf-16(null);akt-1(null) double-mutant animals (Figures 4B and Figure S2). As previously shown (Zhang et al 2008; Alam et al 2010; Dumas et al 2010), DAF-16A::GFP was nuclear in many akt-1(null) animals cultured on E. coli containing a control RNAi construct. Exposure of animals of the same genotype to dpy-21 RNAi promoted the nuclear export and cytoplasmic retention of DAF-16A::GFP.…”

“…In C. elegans , the EAK proteins comprise a conserved pathway that acts in parallel to AKT-1 to control the activity of nuclear DAF-16/FoxO (Williams et al 2010). eak mutations, while causing a weak dauer-constitutive phenotype in isolation, strongly enhance the dauer-constitutive phenotype caused by akt-1 mutations (Hu et al 2006; Zhang et al 2008; Alam et al 2010; Dumas et al 2010). EAK-7, which is likely the most downstream component of the EAK pathway, is a conserved protein of unknown function that is expressed in the same tissues as DAF-16/FoxO.…”

The Rieske oxygenase DAF‐36 functions as a cholesterol 7‐desaturase in steroidogenic pathways governing longevity

“…Null mutations of daf-9 abolish DA production entirely, and animals constitutively enter the dauer diapause with complete penetrance (Gerisch et al 2001; Jia et al 2002). HSD-1, a 3-hydroxysteroid-dehydrogenase homolog with weaker phenotypes than daf-9 , is proposed to make the 3-keto steroid 4-cholesten-3-one in the synthesis of Δ 4 -DA, but there is as of yet no biochemical evidence for this activity (Patel et al 2008; Dumas et al 2010). DAF-36 is a Rieske-like oxygenase implicated in DA biosynthetic pathways, the loss of which also results in less severe phenotypes than daf-9 , suggesting it acts in early biosynthetic branches that converge on DAF-9/CYP450 (Rottiers et al 2006).…”

Signaling in Parasitic Nematodes: Physicochemical Communication Between Host and Parasite and Endogenous Molecular Transduction Pathways Governing Worm Development and Survival

“…In the absence of ligand, DAF-12, in concert with the co-repressor DIN-1 promotes dauer arrest [48] and confers lifespan extension. Genetic epistasis analysis [82], reverse genetic [83] and biochemical [48] evidence confirm that DAF-12 signaling operates downstream of ILS and TGFβ-like signaling, and likewise, both ILS and TGFβ-like signaling positively regulate biosynthesis of dafachronic acids, principally by upregulating expression of the cytochrome P450 DAF-9. Like GPCR signaling and ILS, regulatory elements constituting DAF-12 signaling appear to be conserved in parasites and, based on current evidence, to undertake functions that are consistent with their dauer regulatory functions in C. elegans .…”