A previous study using the genome-wide ChIP-on-chip analysis has identified 16 genes as direct transcriptional targets of NPAS2 in breast cancer cells, among which 4 genes including CDC25A, ELF4, CDKN2AIP and POU4F2 were involved in cell proliferation and apoptosis regulation.13 Therefore, functional roles of NPAS2 in the transcriptional regulation of these genes were determined in HCC cells. The gene discussed is POU4F2; the disease is breast cancer.