br Keywords br Gastric cancer br RUNX br
In the present study, two circular RNA (circRNA) expression profiles in paired gastric cancer (GC) tissues from the GEO database were examined. We identified a novel circRNA, has_circ_0001461, which we termed circFAT1(e2). We verified that circFAT1(e2) was significantly downregulated in GC tissues and cell lines and was correlated with overall survival of GC patients. Fluorescence in situ hybridization (FISH) analysis showed that circFAT1(e2) was distributed in the cytoplasm of GC cells, as well as in the nucleus. Functional assays indicated that overexpression of circFAT1(e2) inhibited GC cell proliferation, migration and invasion. Then, we in-vestigated whether circFAT1(e2) acts as a sponge of microRNA-549g(miR-548g) and regulates the expression of tumor suppressor RUNX1 in GC cells. Moreover, we found that nucleus-located circFAT1(e2) could directly interact with Y-box binding protein-1 (YBX1) and inhibit its function. In conclusion, circFAT1(e2) may play a role as a tumor suppressor in GC Doxorubicin by regulating the miR-548g/RUNX1 axis in the cytoplasm and targeting YBX1 in the nucleus.
As one of the most frequently occurring gastric diseases, gastric cancer (GC) is considered to be the most serious threat to the health and even the life of patients [1,2]. Although diagnosis and therapy tech-nologies have been developing rapidly, the prognosis of GC is still poor in recent years [3,4]. A lack of eﬀective diagnostic measures and bio-markers for GC may be the most important reason . Therefore, elucidating the underlying molecular mechanisms of GC initiation and progression is extremely necessary for the screening of proper bio-markers and the development of eﬀective therapeutic measures for GC patients.
Noncoding RNAs (ncRNAs), including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), were in-itially considered to be meaningless for the development of GC [6–8]. However, with more and more research available, the functions of
ncRNAs have begun to change from a useless type of RNA to an im-portant gene regulator [6,9,10]. A vast amount of studies have de-monstrated that ncRNAs may be involved in the tumorigenesis of many human tumors, such as breast cancer, lung cancer, and liver cancer, by controlling the expression of oncogenes and tumor suppressor genes [11–13]. In particular, circRNAs, which are characterized by covalently closed continuous loops without 5′ to 3’ polarity and a polyadenylated tail, were revealed to exert regulatory eﬀects on gene expression in many human cancers [14,15]. They were proven to function as com-peting endogenous RNAs to regulate miRNA levels and aﬀect the tar-geted gene expression [16,17]. However, the roles of circRNAs in the progression of GC are still largely unknown.
In our study, we analyzed the data of two independent microarray datasets (GES100170 and GSE83521) from the Gene Expression Omnibus database and identified that circFAT1(e2) was significantly downregulated in GC tissues and cell lines and predicted a better
∗ Corresponding author. Department of General Surgery, The First Aﬃliated Hospital of Soochow University, No. 188 Shizi Street, Suzhou, 215006, Jiangsu Province, PR China.
prognosis of GC patients. We found that circFAT1(e2) was distributed not only in the cytoplasm of GC cells but also in the nucleus. The circFAT1(e2) circRNA could inhibit GC tumor growth by acting as a sponge of miR-548g in the cytoplasm and binding to the YBX1 protein in the nucleus. Hence, circFAT1(e2) may serve as an eﬀective inhibitor and biomarker for GC therapy and diagnosis.
2. Materials and methods
2.1. Patient tissue samples and cell lines