On the basis of our previous finding that expression of kappa light chain in NPC cells can be upregulated by EBV-encoded latent membrane protein 1(LMP1) through the activation of NF-κB and AP-1 signaling pathways, we thus use NPC cells as model to further explore the molecular mechanisms of nonlymphoid cells expressing Ig kappa. Here, FOS is linked to nasopharyngeal carcinoma.