Leukemia inhibitory factor promotes nasopharyngeal carcinoma progression and radioresistance
Shu-Chen Liu, … , Kai-Ping N. Chow, Yu-Sun Chang
Shu-Chen Liu, … , Kai-Ping N. Chow, Yu-Sun Chang
Published November 25, 2013
Citation Information: J Clin Invest. 2013;123(12):5269-5283. https://doi.org/10.1172/JCI63428.
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Research Article

Leukemia inhibitory factor promotes nasopharyngeal carcinoma progression and radioresistance

Abstract

Radioresistance of EBV-associated nasopharyngeal carcinoma (NPC) is associated with poor prognosis for patients with this form of cancer. Here, we found that NPC patients had increased serum levels of leukemia inhibitory factor (LIF) and that higher LIF levels correlated with local tumor recurrence. Furthermore, in vitro studies with NPC cells and in vivo xenograft mouse studies demonstrated that LIF critically contributes to NPC tumor growth and radioresistance. Using these model systems, we found that LIF treatment activated the mTORC1/p70S6K signaling pathway, enhanced tumor growth, inhibited DNA damage responses, and enhanced radioresistance. Treatment with either soluble LIF receptor (sLIFR), a LIF antagonist, or the mTOR inhibitor rapamycin reversed LIF-mediated effects, resulting in growth arrest and increased sensitivity to γ irradiation. Immunohistochemical (IHC) analyses of human NPC biopsies revealed that LIF and LIFR were overexpressed in tumor cells and that LIF expression correlated with the presence of the activated p-p70S6K. Finally, we found that the EBV-encoded protein latent membrane protein 1 (LMP1) enhances LIF production. Together, our findings indicate that LIF promotes NPC tumorigenesis and suggest that serum LIF levels may predict local recurrence and radiosensitivity in NPC patients.

Authors

Shu-Chen Liu, Ngan-Ming Tsang, Wen-Che Chiang, Kai-Ping Chang, Chuen Hsueh, Ying Liang, Jyh-Lyh Juang, Kai-Ping N. Chow, Yu-Sun Chang

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Figure 4

LIF-induced activation of p70S6K is mediated through mTOR.

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LIF-induced activation of p70S6K is mediated through mTOR. (A and B) Inh...
(A and B) Inhibitors of mTOR suppressed the LIF-induced phosphorylation of p70S6K. CNE1 cells (A) and TW06 cells (B) were pretreated with inhibitors for 40 minutes, and then stimulated with LIF (10 ng/ml). Ten minutes later, the cells were harvested and protein lysates were obtained. (C) Real-time monitoring of cell viability. CNE1 cells were pretreated with everolimus for 40 minutes and then stimulated with LIF (10 ng/ml) for the duration of the experiment. Values are expressed as the mean and SD of triplicate experiments. (D) siRNA-mediated depletion of mTOR in CNE1 cells inhibits the LIF-induced activation of p70S6K. Cells were stimulated with LIF at 24 hours after siRNA transfection. NC, negative control siRNA. (E) Silencing of mTOR by siRNA suppresses the effects of LIF on CNE1 cell proliferation. Cells were replated into E-plate at 24 hours after siRNA transfection. Values of cell growth were normalized with respect to the time of LIF addition. Data are presented as means and SD of triplicate experiments. (F) Pretreatment with sLIFR 2 hours prior to LIF treatment decreases LIF-induced phosphorylation of mTOR in both CNE1 cells and TW06 cells. GAPDH was used as the loading control for Western blotting. (G) Inhibition of p70S6K by rapamycin suppresses LIF-mediated tumor growth in mice (n = 5 for LIF treatment only, an n = 6 for rapamycin plus LIF treatment). Rapamycin was given by intraperitoneal injection (3 mg/kg, once a day, 5 days/week × 3 weeks). (H) Quantification of the total photon fluxes of tumors shown in G. *P < 0.05; **P < 0.01, paired t test.