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Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer
Institute, Bethesda, MD, USA
Many cells in our body reside in a quiescent state (G0), serving as a crucial reserve for tissue
homeostasis and repair. The decision to exit quiescence is highly regulated, requiring cells to
coordinate two seemingly contradictory imperatives: favoring glycolysis for biomass
accumulation while maintaining activity of the ubiquitin-ligase APC/C-CDH1 to ensure genomic
stability. Paradoxically, APC/C-CDH1 targets key glycolytic enzymes for degradation, actively
inhibiting the metabolic pathway needed for growth. How cells coordinate these mutually
exclusive demands remains a fundamental question in cell biology.
By developing a suite of live-cell biosensors and automated single-cell tracking pipelines, we
provide the first real-time visualization of this coordination. We reveal that individual cells
resolve this conflict through an incoherent feedforward loop that functions as an intrinsic
metabolic checkpoint. After external cues initiate exit, the rapid, nutrient-sensing activity of
mTOR mediates phosphorylation of the APC/C adapter CDH1. Using our high-resolution
imaging tools, we observed that this phosphorylation causes CDH1 to partially dissociate from
the APC/C complex, leading to a transient inactivation of the ligase.
Crucially, this transient window allows for the rapid accumulation of PFKFB3, a rate-limiting
glycolytic enzyme, promoting a potent "pulse" of glycolytic activity required for proliferation
commitment. Delayed accumulation of phosphatase activity eventually restores full APC/C
activity, shifting cells back toward oxidative phosphorylation. Through the application of these
new quantitative tools, we demonstrate that proliferation commitment is critically dependent on
this precise, transient metabolic shift. Our findings define a novel regulatory axis and provide a
robust technical framework for modulating cell fate in human health and disease. |