Proximity labeling of DAF-16 FOXO highlights aging regulatory proteins.

Insulin/insulin-like growth factor signaling inhibits FOXO transcription factors to control development, homeostasis, and aging. Here, we use proximity labeling to identify proteins interacting with the C. elegans FOXO DAF-16. We show that in well-fed, unstressed animals harboring active insulin signaling, DAF-16 forms a complex with the PAR-1/MARK serine/threonine kinase, a key regulator of cell polarity. PAR-1 inhibits DAF-16 accumulation and promotes DAF-16 phosphorylation at S249, at a conserved motif that PAR-1/human MARK2 phosphorylates in vitro. DAF-2 insulin-like receptor signaling stimulates DAF-16 S249 phosphorylation, suggesting DAF-2 activates PAR-1. DAF-2 also promotes PAR-1 expression by inhibiting DAF-16. PAR-1 knockdown, or DAF-16 S249A, prolong lifespan, whereas phosphomimetic DAF-16 S249D suppresses the longevity of daf-2 mutants. At low insulin signaling, DAF-16 proximity labeling highlights transcription factors, chromatin regulators, and DNA repair proteins. One interactor, the zinc finger/homeobox protein ZFH-2/ZFHX3, forms a complex with DAF-16 and prolongs lifespan. Our work provides entry points for hypothesis-driven studies of FOXO function and longevity.