Abstract
BackgroundAs a novel class of noncoding RNAs, circRNAs have been recently identified to regulate tumorigenesis and aggressiveness. However, the function of circRNAs in colorectal cancer (CRC) metastasis remains unclear. We aimed to identify circRNAs that are upregulated in CRC tissues from patients and study their function in CRC metastasis.MethodsWe compared six pairs of CRC tissues and their matched adjacent non-tumor tissues by using circRNA microarray. We first evaluated the expression of circPTK2 (hsa_circ_0005273) in fresh tissues from CRC tumors and corresponding adjacent tissues by qPCR analysis. CircPTK2 expression levels in the tissue microarray with 5 years of survival information were determined by RNA-ISH analysis. Meanwhile, the expression levels of circulating circPTK2 were further analyzed according to the patients’ clinical features. We analyzed cell apoptosis, colony formation, migration, and invasion in CRC cells. To further elucidate the effect of circPTK2 in CRC metastasis, we also conducted a colon cancer hepatic and pulmonary metastasis experiment. We used RNA biotin-labeled pull down and mass spectrometry to identify the target of circPTK2. We established a PDTX model to evaluate the effect of shRNA specifically targeting circPTK2 on tumor metastasis.ResultsWe identified a novel circRNA, circPTK2, which is back-spliced of three exons (exons 27, 28 and 29) of PTK2 by using circRNA microarray, bioinformatics and functional studies. CircPTK2 was elevated in CRC tissues and positively associated with tumor growth and metastasis. CRC patients with increased circPTK2 expression were positively correlated with poorer survival rates. Furthermore, our studies showed that circPTK2 could promote EMT of CRC cells in vitro and in vivo by binding to vimentin protein on sites Ser38, Ser55 and Ser82. We further demonstrated the interaction of circPTK2 and vimentin mediated the regulation of CRC by knockdown or overexpression of vimentin. In addition, we revealed that tail vein injection of shRNA specifically targeting circPTK2 blunt tumor metastasis in a patient-derived CRC xenograft model.ConclusionsCollectively, these results demonstrate that circPTK2 exerts critical roles in CRC growth and metastasis and may serve as a potential therapeutic target for CRC metastasis, and also a promising biomarker for early diagnosis of metastasis.
Highlights
As a novel class of noncoding RNAs, circRNAs have been recently identified to regulate tumorigenesis and aggressiveness
We found that circPTK2 was elevated in colorectal cancer (CRC) tissues and positively associated with tumor growth and metastasis
We identified that circPTK2 is a promising biomarker for early diagnosis of CRC metastasis and provides a potential therapeutic target for CRC
Summary
As a novel class of noncoding RNAs, circRNAs have been recently identified to regulate tumorigenesis and aggressiveness. The function of circRNAs in colorectal cancer (CRC) metastasis remains unclear. Several circRNAs have been found to be associated with CRC tumorigenesis or metastasis, such as circCCDC66, hsa_circ_001569, ciRS-7A, and circHIPK3 [15,16,17,18,19]. These studies demonstrate that the regulation of circRNA expression is tightly controlled under distinct circumstances, and that the investigations into circRNA are still in their infancy. The functions and underlying mechanisms of circRNAs in the epithelial–mesenchymal transition (EMT) process of human cancers, such as CRC, remain unclear. EMT converts epithelial cells to a mesenchymal-like phenotype and is associated with the loss of cell contacts, production of the type-III intermediate filament protein vimentin, and increases in cell migration and invasion [22]
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