Putrescine functions as a metabolic checkpoint in replication stress-induced senescence.

Cellular senescence represents a fundamental biological response to replication stress and other genotoxic insults, acting as both a barrier to malignant transformation and a driver of age-related tissue dysfunction. Here, we dissect the metabolic remodeling that accompanies senescence triggered by sustained activation of the replication licensing factor CDC6. Induction of CDC6 in human bronchial epithelial cells provoked a biphasic response characterized by transient hyperproliferation followed by accumulation of senescence-associated β-galactosidase-positive cells. Targeted metabolomics revealed an early increase in intracellular putrescine that was followed by pronounced decline at senescence onset. Functional studies demonstrated that putrescine supplementation attenuated CDC6-induced senescence, whereas knockdown of ODC1, the rate-limiting enzyme in putrescine biosynthesis, accelerated it and increased TP53 accumulation. Mechanistically, CDC6 controls the ODC1-putrescine axis through ERK and GSK3β-mediated regulation of MYC, whereby early-phase ERK signaling stabilizes MYC to enhance polyamine biosynthesis, while prolonged CDC6 activation triggers GSK3β-dependent MYC degradation, ODC1 downregulation, and commitment to senescence. Targeted re-analysis of publicly available single-cell RNA-sequencing datasets from COVID pneumonia patients revealed elevated CDC6 expression alongside reduced MYC and ODC1 levels in alveolar epithelial cells exhibiting markers of senescence. Collectively, these findings identify putrescine as a metabolic checkpoint in replication stress-induced senescence and reveal a MYC-orchestrated signaling-metabolic circuit that temporally integrates oncogene activation with cell fate decisions.