EBV-LMP1 targeted DNAzyme enhances radiosensitivity by inhibiting tumor angiogenesis via the JNKs/HIF-1 pathway in nasopharyngeal carcinoma.

Lifang Yang,Deyun Feng,Lanbo Xiao,Ya Cao,Zigang Dong,Weihua Liao,Min Tang,San Xu,Jingchen Lu,Lunquan Sun,Liyu Liu,Zhijie Xu,Ann M Bode,Xiangjian Luo,Xin Dong

doi:10.18632/oncotarget.3331

Abstract

LMP1, which is encoded by the Epstein-Barr virus, is proposed to be one of the major oncogenic factors involved in nasopharyngeal carcinoma (NPC). Previous studies demonstrated that down-regulation of LMP1 by LMP1-targeted DNAzyme (DZ1) increases the radiosensitivity of NPC. However, the mechanism by which DZ1 contributes to this radiosensitivity remains unclear. In this study, we determined whether a DZ1 blockade of LMP1 expression has an overall positive effect on the radiotherapy of NPCs by repressing HIF-1/VEGF activity and to investigate the mechanisms underlying LMP1-induced HIF-1 activation in NPC cells. The results showed that DZ1 inhibited the microtubule-forming ability of HUVECs co-cultured with NPC cells, which occurs with the down-regulation of VEGF expression and secretion. Moreover, LMP1 increases phosphorylated JNKs/c-Jun signaling, which is involved in the regulation of HIF-1/VEGF activity. After silencing LMP1 and decreasing phosphorylation of JNKs, NPC cells exhibited an enhanced radiosensitivity. Furthermore, in vivo experiments revealed a significant inhibition of tumor growth and a marked reduction of the Ktrans parameter, which reflects the condition of tumor micro-vascular permeability. Taken together, our data suggested that VEGF expression is increased by LMP1 through the JNKs/c-Jun signaling pathway and indicated that DZ1 enhances the radiosensitivity of NPC cells by inhibiting HIF-1/VEGF activity.

Highlights

Nasopharyngeal carcinoma (NPC) is a malignancy most strongly associated with the Epstein-Barr virus (EBV), and radiotherapy is the most effective treatment against NPC
The results showed that the well-differentiated LMP1negative NPC cell line, CNE1, was not able to form tubular structures in Matrigel, whereas two LMP1positive NPC cell lines, CNE1-Latent membrane protein 1 (LMP1) and HNE2-LMP1, could form tubular structures
This indicates that LMP1 knock-down by DZ1 in co-cultures resulted in reduced vascular endothelial growth factor (VEGF) expression and inhibition of tube-formation (Fig. 1A, V-VIII, B)

Summary

Introduction

Nasopharyngeal carcinoma (NPC) is a malignancy most strongly associated with the Epstein-Barr virus (EBV), and radiotherapy is the most effective treatment against NPC. Due to radioresistance, locoregional recurrence or metastatic spread still occurs in a high proportion of patients who undergo radiotherapy [1]. Latent membrane protein 1 (LMP1) is an EBVencoded protein with oncogenic properties [2]. LMP1 plays an essential role in tumorigenesis of NPCs through the activity of various signal pathways and is a potential target for NPC biotherapy [3,4,5]. Downregulation of LMP1 was shown to be potentially effective www.impactjournals.com/oncotarget in the prevention of NPC metastasis and reduction of NPC radioresistance [6, 7]. The mechanism of LMP1mediated radioresistance is not entirely clear

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Results

Conclusion