A study of cell survival mechanisms for apoptosis-resistant oral squamous cell carcinoma cell line

乳铁蛋白（Lactoferrin, Lfn）具有多种生物学功能，不仅可以防御宿主细菌和病毒，还可以防御恶性肿瘤。我们之前报道了Lfn肽（Lfn-p），由酸性胃蛋白酶水解Lfn产生，通过JNK激活诱导人口腔鳞状细胞癌细胞系（SAS）凋亡。（Sakai et al., J Pharmacol Sci 98,2005）相反，我们发现lf -p诱导的其他鳞状细胞癌细胞系HSC-4的磷脂酶D （PLD）激活在lf -p治疗下存活。在本研究中，我们检测了小干扰RNA （siRNA）敲低内源性PLD对HSC-4细胞中Lfn-p激活的存活信号的影响。细胞中均表达PLD1和pl2。通过siRNA转染降低PLD1而非PLD2的表达水平，抑制了lfn -p诱导的PLD活性。lfn -p诱导的Akt磷酸化，众所周知的生存信号也被PLD活性抑制。此外，在PLD1敲低的细胞中，HSC-4细胞中JNK磷酸化伴随lfn -p诱导的凋亡增加。这些结果表明，PLD1在HSC-4细胞中通过PI3K/Akt /JNK通路参与细胞存活。

Lactoferrin (Lfn) show multi biological function including host defense against not only bacteria and virus but also malignant neoplasm. We previously reported that Lfn peptides (Lfn-p), produced by acid-pepsin hydrolysis of Lfn, induced apaptosis through JNK activation in human oral squamous cell carcinoma cell lines, SAS. (Sakai T et al., J Pharmacol Sci 98,2005) In contrast, we found that Lf-p-induced phospholipase D (PLD) activation in other squamous cell carcinoma cell line, HSC-4, survived in Lf-p-treatment. In the present study, we examined the effect of knockdown of endogenous PLD by small interference RNA (siRNA) on survival signaling activated with Lfn-p in HSC-4 cells. Both PLD1 and 2 were expressed in the cells. The reduction of expression level of PLD1, not PLD2, by siRNA transfection suppressed Lfn-p-induced PLD activity. Lfn-p-induced Akt phosphorylation, well-known survival signaling were also suppressed with PLD activity. Furthermore, JNK phosphorylaiton accompanied by Lfn-p-induced apoptosis in HSC-4 cells was increased in PLD1 knockdown cells. These results suggested that PLD1 was involved in cell survival through PI3K/Akt /JNK pathway in HSC-4 cells.