It also upregulated the expression of protein kinase RNA-like endoplasmic reticulum kinase/inositol-requiring enzyme 1α/activating transcription factor 4 (PERK/eIF2α/ATF4), a pivotal pathway in the unfolded protein response (UPR) across various HCC cell lines, thereby intensifying the UPR signaling triggered by radiation. The gene discussed is ATF4; the disease is hepatocellular carcinoma.