SPI1 and nasopharyngeal carcinoma: However, the lack of haematopoietic cell lineage-specific transcription factors, PU.1 and IRF-4, in NPC cell lines, combined with our EMSA results leads us to speculate that the transcription factor Ets-1 might cooperate with other IRFs to bind the EICE element of the 3′Eκ to modulate kappa gene expression in a manner different from B cell lines.