Together, these findings suggest a suppressive role of RSU1 in ERK activation, which provides an explanation as to why loss or reduced expression or mutations of RSU1 was often found in human cancers (e.g., hepatocellular carcinoma and gliomas) (37, 38, 39) and why overexpression of RSU1 can inhibit anchorage-independent growth of human cancer cells (39, 40). Here, RSU1 is linked to hepatocellular carcinoma.