ATF4 and hepatocellular carcinoma: It has been reported that the small protein of HBsAg expression in HCC cells induces endoplasmic reticulum (ER) stress that stimulates the activating transcription factor 4 (ATF4) to increase the expression and secretion of fibroblast growth factor 19 (FGF19), which in turn activated JAK2/STAT3 signalling 53.