Abstract 4720: Novel findings for the clinical significance of RNA editing status of AZIN1 and ADAR 1 and 2 expression levels in gastric cancer patients
Authors: Okugawa Yoshinaga , Toiyama Yuji , Shigeyasu Kunitoshi , Ichikawa Takashi , Oki Satoshi , Mori Koichiro , Nagano Yuka , Yasuda Hiromi , Yoshiyama Shigeyuki , Ohi Masaki , Tanaka Koji , Inoue Yasuhiro , Araki Toshimitsu , Mohri Yasuhiko , Tanaka Motoyoshi , Miki Chikao , Goel Ajay , Kusunoki Masato 
Published: July 2017

Background. Despite recent advances in surgical techniques and treatment options, gastric cancer (GC) remains the third most common cause of cancer-related deaths worldwide. Besides DNA sequence mutations, epigenetic alterations have emerged as significantly major players in cancer development. A-to-I RNA editing is a post-transcriptional modification that converts adenosines to inosines in both coding and noncoding RNA transcripts, and has recently been recognized has a novel epigenetic mechanism in GC pathogenesis. More specifically, A-to-I editing of AZIN1 transcripts was shown to be regulated by an adenosine deaminase acting on RNA-1 (ADAR1), and edited AZIN1 resulted in an aggressive phenotype during disease progression in some human cancers. The aim of this study was to clarify the clinical consequences of RNA editing status of AZIN1 and the RNA editing enzymes (ADAR1 and 2) in GC patients.

Methods. Two hundred eighty-eight gastric specimens from one hundred forty-four patients who underwent surgery for GC were evaluated. We analyzed the RNA editing status of AZIN1 by RNA editing site-specific quantitative PCR (RESSqPCR). RESSqPCR allows quantitation of RNA editing levels using wild-type or edited AZIN1-specific primers, and RNA editing levels are calculated by determining the ratios of Ct values between edited vs. wild-type transcript expression levels. Furthermore, expression levels of ADAR1 and ADAR2 were evaluated by qPCR in GC tissues.

Results. We observed a higher frequency of the AZIN1 RNA editing in tumors compared with normal mucosa in GC. RNA editing status of AZIN1 was significantly increased in a stage-dependent manner, and high frequency of RNA editing in AZIN1 significantly correlated with advanced T stage and presence of lymph node metastasis in GC patients. Multivariate analysis revealed that high frequency of RNA editing in the AZIN1 gene was an independent prognostic factor for poor disease free survival and overall survival. Furthermore, significant upregulation of ADAR1 and downregulation of ADAR2 was also observed in GC tissues compared with matched normal mucosa, and these alterations also significantly correlated with disease progression factors and poor prognosis in GC patients. Interestingly, ADAR1 expression level was positively correlated with RNA editing status of AZIN1 in GC tissues.

Conclusions. Our findings revealed that altered gene-specific A-to-I editing events mediated by ADAR1 promote disease progression in GC. We conclude that assessment of RNA editing status of the AZIN1 gene might offer a novel and superior biomarker for a more accurate diagnosis of disease staging and may help predict clinical outcomes in GC patients.

Citation Format: Yoshinaga Okugawa, Yuji Toiyama, Kunitoshi Shigeyasu, Takashi Ichikawa, Satoshi Oki, Koichiro Mori, Yuka Nagano, Hiromi Yasuda, Shigeyuki Yoshiyama, Masaki Ohi, Koji Tanaka, Yasuhiro Inoue, Toshimitsu Araki, Yasuhiko Mohri, Motoyoshi Tanaka, Chikao Miki, Ajay Goel, Masato Kusunoki. Novel findings for the clinical significance of RNA editing status of AZIN1 and ADAR 1 and 2 expression levels in gastric cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4720. doi:10.1158/1538-7445.AM2017-4720