MAPK3 and hepatocellular carcinoma: The MAPK/ERK pathway is another frequently abnormally activated signaling pathway in HCC, and the activation of this pathway usually begins with the binding of cell surface receptors, such as growth factor receptors, to ligands, activation of ERK1/2 by phosphorylation via the RAS/RAF/MAP kinase-ERK kinase (MEK)/ERK cascade, and then to the nucleus to regulate the transcription of target genes (Roberts and Der, 2007).