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Abstract Anabolic and catabolic processes are coordinated by a conserved regulatory network, which includes the nutrient-sensing protein kinase mTOR complex 1 (mTORC1) and the insulin- and stress-responsive transcription factor FoxO. In a physiological setting, these regulators align growth, storage, reproduction, and aging with nutrient availability. Here, we identify transcription factor Spalt-related (Salr), previously implicated in organogenesis, as a negative regulator of growth and lipid storage in Drosophila melanogaster . Salr activates catabolic gene expression and restricts mTORC1-mediated cell growth in the Drosophila fat body. The genomic binding of Salr overlaps extensively with that of FoxO, and a similar convergence is observed for their mammalian homologs, SALL1 and FOXO1. Both Salr and FoxO are activated upon fasting, but respond to distinct cues: while FoxO displays transient activation and is responsive to AKT inhibition, Salr is activated in a slow and sustained manner through the integrated stress response. Once activated, Salr counters nuclear localization of FoxO. Taken together, we show that Salr and FoxO are growth-inhibitory transcription factors that act in a convergent manner to respond to nutrient stress through distinct cues.
Deniz et al. (Sat,) studied this question.