Neutrophil lactoferrin upregulates the human p53 gene through induction of NF-κB activation cascade

Neutrophil lactoferrin (Lf) was previously shown to act as a transcriptional activator in various mammalian cells. Here, we describe that Lf specifically transactivates the p53 tumor suppressor gene through the activation of nuclear factor-κB (NF-κB) and consequently regulates p53-responsive oncogenes. In HeLa cervical carcinoma cells stably expressing Lf (HeLa-Lf), expression of mdm2 and p21^waf1/cip1 as well as p53 was greatly enhanced. Transient expression of Lf also markedly transactivates transcription of a p53 promoter-driven reporter and NF-κB-driven reporters in various mammalian cells. However, mutation of the NF-κB site or treatment with an NF-κB inhibitor abrogated the transactivation, suggesting that NF-κB should play an essential role in the Lf-induced transactivation. Increased binding activity and nuclear translocation of p65 in response to Lf strongly support these findings. Furthermore, Lf-mediated NF-κB activation is diminished in IKKα- or IKKβ-deficient mouse embryonic fibroblast cells. The activation of both IKKs and NF-κB by Lf is over-ridden by the expression of dominant-negative mutants of NIK, MEKK1, IKKα and IKKβ. Collectively, we conclude that overexpressed Lf directly relays signals to upstream components responsible for NF-κB activation, thereby leading to the activation of NF-κB target genes.