ATF4 and cancer: Although the PS state has been identified and explored across multiple tissue origins in immortalized cancer cells[13–15], the bulk of PS research has been conducted in PC9 cells[16], in which it was demonstrated that a cascade initiated by mini-mitochondrial-outer-membrane permeabilization (mini-MOMP) and culminating in upregulation of activating transcription factor 4 (ATF4) drives PSPC9 formation[17].