ABCG2 and cancer: Furthermore, given the essential role of WDR5 in mediating the tri-methylation of H3K4 and transcriptional activation of target genes involved in pluripotency, development and cancer, and H3K4me3 functioning as a key histone modification that often selectively localizes to target gene promoters to activate target gene transcription [44,45], we explored and confirmed the dependence of TOX3 on the methyltransferase activity of WDR5 and tri-methylation of H3K4 mediated by it during the activation of ABCG2 transcription.