MAPK1 and nasopharyngeal carcinoma: Interestingly, treatment of RKIP knockdown CNE2 cells with MEK inhibitor U0126 (Promega, Madison, WI, USA) decreased phospho-AKT level, whereas transfection of ERK-2 expression plasmid into RKIP overexpression CNE2-IR cells significantly increased phospho-AKT level after 4Gy irradiation, suggesting that AKT is a downstream transducer of ERK signaling in the RKIP-regulating signaling pathways of irradiated NPC cells (Figure 6A).