DAF-16/FOXO and HLH-30/TFEB function as combinatorial transcription factors to promote stress resistance and longevity

To survive nature’s daily challenges, organisms need the ability to perceive a broad variety of harmful conditions and to respond to these accordingly. The transcription factor DAF-16/FOXO has long been considered a predominant central nexus in these pathways, relaying distress signals into customized transcriptional changes, driving the expression of stress resistance and longevity promoting genes. However, DAF-16’s sufficiency in fulfilling this complex task has remained unclear. Using C. elegans as a model system, we show that DAF-16 does not function alone but needs to synergize as a combinatorial transcription factor with HLH-30/TFEB, a master regulator of autophagy and lysosome biogenesis. Under harmful conditions, DAF-16 and HLH-30 both translocate into the nucleus, form a complex, and co-occupy many target promoters. Consistently, they co-regulate many target genes. Interestingly though, the genetic interaction between these transcription factors depends on the upstream stimulus and carefully tunes the physiological outcomes for the animal: i.e. they rely on each other, functioning in the same pathway, to promote longevity or resistance to oxidative stress, but they elicit heat stress responses independently, and they even oppose each other during dauer formation. We suggest that an organism’s full integration of nature’s diverse distress signals and the resulting induction of stimulus-specific responses relies on a module comprised of DAF-16 and HLH-30, which perceives stimuli convergent on either transcription factor and by combinatorial regulation elicits expression of specific target gene sets that ensure optimal survival under each given threat.