ATF4 and cancer: OXPHOS dysfunction often leads to upregulation of activating transcription factor (ATF4) and suppression of mammalian target of rapamycin (mTOR) in cancer cells.[3, 30, 31, 32] Consistently, we detected a quick and robust activation of ATF4 and suppression of mTOR (reflected by pS6 reduction) upon OXPHOS inhibition in sensitive cancer cells (NCI‐H82, G‐401, and WSU‐DLCL2) when they were treated with Gboxin, Oligomycin A, or Berberine (Figure 1F; Figure S1E, Supporting Information).