Although we have demonstrated the heterodimerization of c-Jun and c-Fos (Fig. 7) and this heterodimer can directly bind to the AP-1 site located near the iEκ enhancer (Fig. 8C), we have used only c-Jun and c-Fos in this report, therefore, other dimeric forms of AP-1 transcription factor involved in regulating the iEκ activity in NPC cells can not be excluded at this time. This evidence concerns the gene FOS and nasopharyngeal carcinoma.