RXRA and hepatocellular carcinoma: Initially, we showed that the RXRαprotein is anomalously phosphorylated at a specific site of theserine/threonine residues and is accumulated both in human HCC tissue as wellas in HCC cell lines [22].Phosphorylation at serine 260 of RXRα,a consensus site of mitogen-activated protein kinase (MAPK), is closely linkedto its retarded degradation, low transcriptional activity, and the promotion ofcancer cell growth, and the abrogation of phosphorylation by MAPK-specificinhibitors restores the degradation of RXRαin a ligand-dependent manner [22, 25].