ATF4 and bladder transitional cell carcinoma: In addition, we observed an upregulation of ER stress pathway proteins, including 78-kilodalton glucose regulated protein (GRP78/BiP), p-PERK, eIF2α, p-eIF2α and ATF4 after treating BLCA cells with bacitracin, a kind of P4HB inhibitor, which suggested that the inhibition of P4HB activated the PERK/eIF2α/ATF4/CHOP signaling pathway [18] (Fig. 2).