SP1 and hepatocellular carcinoma: CK19 expression in HCC is regulated by fibroblast-derived hepatocyte growth factor via the mesenchymal–epithelial transition (MET)–extracellular signal-regulated kinase 1/2 (ERK1/2)–activator protein 1 (AP1) and specificity protein 1 (SP1) axis and is closely associated with α-smooth muscle actin-positive cancer-associated fibroblasts [159].