Taken together, the results indicate that p52/p65 and c-Jun/c-Fos heterodimers can bind to the κB and the AP-1 site of human Ig kappa gene in vitro, respectively, which may be the key events in upregulating the activity of iEκ by LMP1 in NPC cells. The gene discussed is FOS; the disease is nasopharyngeal carcinoma.