Abstract 2189: Inhibition of PIN1 suppresses tumorigenicity of EBV-associated NPC.
Authors: Xu Meng , Chow Chit , Cheung Chartia Ching-Mei , Tsang Chi-Man , Lun Samantha Wei-Man , Yuen Jessie Wai-Fung , Chung Grace Tin-Yun , Tsao Sah-Wah , To Ka Fai , Lo Kwok Wai 
Published: August 2014

Nasopharyngeal carcinoma (NPC) is an EBV-associated epithelial malignancy which is prevalent in southern China and south-east Asia. EBV-encoded EBNA1 is consistently expressed in NPC cells and implicates the replication and stable persistence of latent viral genome. As a phosphorylated protein, the function of EBV is believed to be affected by phosphorylation.In this study, we aimed to investigate whether the phospho-Ser/Thr-Pro specific prolyl-isomerase PIN1 alters EBNA1 function and plays a role in the tumorigenesis of EBV-associated NPC.By western blotting and immunohistochemical staining, we have found that PIN1 was highly expressed in almost all 6 NPC tumor lines and 70 primary tumors. In the EBV-positive C666-1 cells, co-localization and interaction of EBNA1 and PIN1 was detected by immunofluorence staining and co-immunoprecipitation assay respectively. The interaction between PIN1 and EBNA1 at the specific serine-proline motif (Ser383 and Ser393 in EBNA1;WW domain in Pin1) was also demonstrated. To investigate potential role of PIN1 in NPC tumorigenesis, we established a stable nasopharyngeal epitheliacell line NP69 overexpressing PIN1. In this model, we found that overexpression of PIN1 up-regulated cyclin D1 and activated MAPK/JNK pathway. Increased anchorage-independent growth of NP69 overexpressing PIN was shown in soft agar assay.To further validate the oncogencity of PIN1, we knocked down its expression in the NPC cell line C666-1 by RNA interference (siRNA). The study confirmed the PIN1-mediated cyclin D1 suppression. Importantly, knocking down of PIN1 significantly inhibited the cell proliferation, DNA synthesis and migration of NPC cells.Similar findings were also detected in the NPC cells treated with PIN1 inhibitor, Juglone. Treating EBV-positive C666-1cell with Juglone,we found it can significantly induce apoptosisand suppress the cyclinD1expression in C666-1cells. The anti-tumor effect of PIN inhibitor was demonstrated in the in vitro NPC model. To elucidate the anti-tumor potential of PIN1 inhibitorin vivo, the mice implanted with NPC cells were subjected to treatment with different doses of Juglone. A dose-dependent inhibition of tumor growth was observed in the mice treated with PIN1 inhibitor. In conclusion, our findings imply that PIN1overexpression plays important role in the development of NPC. Targeting Pin1 may serve as a potential therapeutic approach for treating patients suffering from this EBV-associated cancer.

Citation Format: Meng Xu, Chit Chow, Chartia Ching-Mei Cheung, Chi-Man Tsang, Samantha Wei-Man Lun, Jessie Wai-Fung Yuen, Grace Tin-Yun Chung, Sah-Wah Tsao, Ka Fai To, Kwok Wai Lo. Inhibition of PIN1 suppresses tumorigenicity of EBV-associated NPC. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2189. doi:10.1158/1538-7445.AM2013-2189