CircFOXK2 Promotes Growth and Metastasis of Pancreatic Ductal Adenocarcinoma by Complexing with RNA-Binding Proteins and Sponging MiR-942

Abstract

The detailed biological functions of circular RNA (circRNA) are largely unexplored. Using circRNA sequencing, we identified 169 differentially expressed circRNA in pancreatic ductal adenocarcinoma (PDAC) cells compared with nontumor human pancreatic ductal epithelial cells. Among them, circFOXK2 was validated with significant upregulation in PDAC cells and 63% of primary tumors (53 of 84). circFOXK2 promoted cell growth, migration, and invasion and was involved in cell-cycle progression and apoptosis. circFOXK2 contained multiple miRNA binding sites, functioning as a sponge for miR-942, which in turn promoted expression of ANK1, GDNF, and PAX6. A novel and highly specific circRNA-pulldown followed by mass spectrometry analysis identified 94 circFOXK2-interacting proteins, which were involved in cell adhesion, mRNA splicing, and structural molecule activity. Of these, circFOKX2 interactions with YBX1 and hnRNPK enhanced expression of oncogenes NUF2 and PDXK. Knockdown of circFOXK2 reduced binding of YBX1 and hnRNPK to NUF2 and PDXK, in turn decreasing their expression. Collectively, our findings demonstrate that circFOXK2 in complex with YBX1 and hnRNPK promotes expression of oncogenic proteins that contribute to PDAC progression.Significance: This study reveals a prominent role for the circRNA circFOXK2 in PDAC progression, suggesting that circFOXK2 might be a novel diagnostic marker for PDAC.

Circular RNA circDLC1 Inhibits MMP1-Mediated Liver Cancer Progression via Interaction with HuR

“…Many studies have demonstrated that circRNAs play regulatory roles via sponging miRNAs and binding proteins (15,16,22,23). To con rm whether circDLC1 serves as "miRNA sponges", RNA immunoprecipitation assays (RIP) were performed in SNU 449 and HCC-LM9 cells using a speci c antibody against argonaute 2 (AGO2).…”

“…Circular RNAs (circRNAs), known as covalently closed and single-stranded transcripts, have been proved to exist in many species (13). Recent studies have reported that circRNAs was aberrantly expressed in many types of cancer, such as HCC (14), gastric cancer (15), and pancreatic ductal adenocarcinoma (16). The main function of circRNAs in tumor is sponging microRNAs (miRNAs), encoding protein or binding protein (14)(15)(16).…”

“…Recent studies have reported that circRNAs was aberrantly expressed in many types of cancer, such as HCC (14), gastric cancer (15), and pancreatic ductal adenocarcinoma (16). The main function of circRNAs in tumor is sponging microRNAs (miRNAs), encoding protein or binding protein (14)(15)(16). Interestingly, more recent studies revealed that methyltransferase-like-3 (METTL3), core complex of methyltransferase, is involved in circRNA biogenesis and function by regulating m6A modi cation (17,18).…”

CircRNA ciRS-7: a Novel Oncogene in Multiple Cancers

“…In addition to miRNA binding, some circRNAs have been found to bind to RNA binding proteins (RBPs) through specific binding sites [39][40][41][42][43]. The study by Dai et al [39] found that the RBP trinucleotide repeat-containing 6A could bind to the flanked intron region of circ0006916 and regulate its biogenesis.…”

“…In addition, circRNAs can bind to proteins to form functional complexes. For example, circFOXK2 could interact with the Y Box binding protein 1 and heterogeneous nuclear ribonucleoprotein K to form a complex, which could enhance NUF2 and PDXK expression in PDAC [42]. Another study showed that circSamd4 could form a complex with PUR proteins to enhance myogenesis through the suppression of myosin heavy chain transcription [43].…”