Lactotransferrin: A candidate tumor suppressor—Deficient expression in human nasopharyngeal carcinoma and inhibition of NPC cell proliferation by modulating the mitogen‐activated protein kinase pathway

Lactotransferrin (LTF) has been shown to regulate tumorogenesis. However, little is known about the role of LTF in regulating the development of human nasopharyngeal carcinoma (NPC). The aim of our study was to investigate whether LTF could regulate the development of NPC by characterizing the pattern of LTF expression in human NPC tissues using cDNA and tissue microarrays. Loss of LTF expression was observed in a significantly higher frequency of NPC tissues compared to that in nontumor nasopharyngeal epithelial tissues. While 61.25% of NPC tissues at the T1/T2 stage were positive for LTF expression, only 40.82% of NPC at the T3/T4 stage were stained by anti-LTF. Similarly, 41.58% of NPC with local lymph node metastasis displayed LTF expression, a value significantly lower than the 46.36% in primary tumors (p < 0.05). These findings suggest that LTF may negatively regulate the development and metastasis of NPC in vivo. Furthermore, overexpression of or treatment with LTF inhibited the proliferation of NPC cells and promoted cell cycle arrest at the G(0)/G(1) phase in vitro. While LTF treatment downregulated expression of cyclin D1 and phosphorylation of retinoblastoma protein (Rb), expression of p21 and p27 in 5-8F NPC cells was enhanced. Moreover, LTF treatment modulated the mitogen-activated protein kinase (MAPK) pathway, but did not affect p53 and STAT3 expression in 5-8F NPC cells. Thus LTF is likely to be a candidate tumor suppressor and downregulates the development of NPC by inhibiting NPC proliferation through induction of cell cycle arrest and modulation of the MAPK signaling pathway. Therefore, our findings provide new insights in understanding the mechanism(s) underlying the action of LTF in regulating the development of human NPC.