To reveal whether 5FU induces ER stress in 5FU-resistant CRC cells, and to determine if PGC-1α regulates ER stress following treatment with 5FU, we assessed the activation of the ER stress markers, including protein kinase-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 alpha (IRE1α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP), in the SNU-C5/5FUR cells after treatment with 5FU. Here, ATF4 is linked to colorectal carcinoma.