E2F6 and neuroblastoma: While the molecular basis for the transcription activator function of HOXC9 in neuroblastoma cells remain to be defined, we showed that the ability of HOXC9 to repress cell cycle genes depended on its interaction with the transcription repressor E2F6, a member of the E2F family of transcription factors that have a critical role in the control of cell proliferation [40].