Senescence-associated dysregulation of translation inhibits activation of the integrated stress response

Senescence is a state of indefinite cell cycle arrest associated with aging, cancer, and age-related diseases. Here we find that translational deregulation and a corresponding maladaptive integrated stress response (ISR) is a hallmark of senescence that desensitizes senescent cells to stress. We present evidence that senescent cells maintain high levels of eIF2? phosphorylation, typical of ISR activation, but translationally repress production of the stress response transcription factor 4 (ATF4) by ineffective bypass of the inhibitory upstream open reading frames (uORFs). Surprisingly, ATF4 translation remains inhibited even after acute proteotoxic and amino acid starvation stressors, resulting in a highly diminished stress response. We also find that stress augments the senescence associated secretory phenotype with sustained remodeling of inflammatory factors expression that is suppressed by non-uORF carrying ATF4 mRNA expression. Our results thus show that senescent cells possess a unique response to stress that entails an increase in their inflammatory profile. Differential gene expression and splicing analysis of long-read direct-RNA analysis for IMR-90 human fibroblasts induced to senescence through etoposide (Etop) or healthy cycling cells (Cyc). Stress-induced effects on senescence were investigated by subjecting senescent cells to acute proteotoxic stress followed by recovery and then harvesting of bulk RNA.