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Research Articles

Differentially expressed genes in radioresistant nasopharyngeal cancer cells: gp96 and GDF15

¹ Department of Radiation Oncology, ² Division of Hematology/Oncology, Department of Internal Medicine, ³ Head and Neck Surgery Section, Department of Otorhinolaryngology, ⁴ Genomic Medicine Research Core Laboratory, ⁵ Department of Obstetrics and Gynecology, ⁶ Department of Pathology, Chang Gung Memorial Hospital, and ⁷ Department of Medical Biotechnology, Chang Gung University, Taoyuan, Taiwan

Requests for reprints: Ann-Joy Cheng, Graduate School of Medical Biotechnology, Chang Gung University, 259 Wen-Hwa 1st Road, Taoyuan 333, Taiwan. Phone: 886-3-2118800, ext. 5085; Fax: 886-3-2118247. E-mail: ajchen{at}mail.cgu.edu.tw

Abstract

Radiotherapy is the major treatment modality for nasopharyngeal cancer (NPC), but in some cases, the disease is radioresistant. We designed this study to identify genes that may be involved in this resistance. We first established two radioresistant subclone cell lines derived from NPC parental cell lines (NPC-076 and NPC-BM1) by treating the cells with four rounds of sublethal ionizing radiation. cDNA microarray analysis was then done, comparing the two resistant cell lines with their corresponding parental cell lines. Seven genes were found to be up-regulated in radioresistant subclones, including gp96 and GDF15, which had shown highest overexpressions. We constructed small interfering RNA plasmids (gp96si and GDF15si) and transfected them into NPC cells to knock down these genes and examine whether this changed their response to radiation. Both gp96si and GDF15si transfectants had radiation-induced growth delay and reduction in colonogenic survival compared with control cells. Knockdown of either gp96 or GDF15 increased the proportion of the cells in G₂-M phase, the most radiosensitive phase of the cell cycle. We have therefore identified at least two genes, gp96 and GDF15, involved in radioresistance of NPC cell lines and showed that knockdown of the genes enhances radiosensitivity. [Mol Cancer Ther 2007;6(8):2271–9]

Grant support: Grant from Chang Gung Molecular Medicine Research Center (CMRPD 140041 for A.J. Cheng) and National Science Research Grant of Taiwan (NSC 95-2314-B-182A-017 for J.T. Chang).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Statement of Significance: To search for radioresistant associated genes in nasopharyngeal cancer (NPC), we established two NPC-radioresistant subclone cell lines and identified seven genes that were up-regulated in radioresistant cells. Two of the highest overexpressed genes, gp96 and GDF15, were further studied. Knockdown of gp96 or GDF15 by small interfering RNA significantly caused radiation-induced growth delay, reduced colonogenic survival, and increased the proportion of the cells in G₂-M phase, the most radiosensitive phase of the cell cycle. These results suggest the roles of these genes in radioresistance and show that the knockdown of the genes enhances radiosensitivity in NPC.

Received 12/27/06; revised 6/11/07; accepted 7/ 2/07.