Regarding the regulatory mechanisms of PN-1 expression in breast cancer cells, we elucidated that epidermal growth factor (EGF), could induce PN-1 up-regulation through the activation of EGFR/PKCδ/MEK/ERK signaling pathway in breast cancer cells, resulting in the up-regulation of EGR1, a newly identified PN-1 transcriptional factor (TF). The gene discussed is EGF; the disease is breast cancer.