Background: As a novel class of non-coding RNAs, circular RNAs (circRNAs) are key regulators of the development and progression of different cancers. However, little is known about the function and biological mechanism of circLMTK2, also named hsa_circ_0001725, in gastric cancer (GC) tumourigenesis. Methods: circLMTK2 was identified in ten paired cancer specimens and adjacent normal tissues by RNA sequencing and genome-wide bioinformatic analysis and verified by quantitative real-time PCR (qRT-PCR). Knockdown or exogenous expression of circLMTK2 combined with in vitro and in vivo assays were performed to prove the functional significance of circLMTK2. The molecular mechanism of circLMTK2 was demonstrated by searching the CircNet database and confirmed by RNA in vivo precipitation assays, western blotting, luciferase assays and rescue experiments. Results: circLMTK2 was frequently upregulated in GC tissues, and high circLMTK2 expression was associated with poor prognosis, lymph node metastasis and poor TNM stage in GC patients. Functionally, circLMTK2 overexpression promoted GC cell proliferation and tumourigenicity in vitro and in vivo. Furthermore, ectopic circLMTK2 expression enhanced GC cell migration and invasion in vitro and tumour metastasis in vivo. In addition, we demonstrated that circLMTK2 could sponge miR-150-5p, thus indirectly regulating the c-Myc expression and contributing to GC tumourigenesis. Conclusion: Our findings demonstrate that circLMTK2 functions as a tumour promoter in GC through the miR-150-5p/c-Myc axis and could thus be a prognostic predictor and therapeutic target for GC.

Colorectal cancer (CRC) is the third most common malignant tumor worldwide and is a serious threat to human health. MicroRNAs (miRNAs) play a key role in oncogenesis and cancer progression. MiRNA-125 (miR-125) is an important miRNA that is dysregulated in several kinds of cancers. Thus, we investigated the expression and effects of miR-125 and Transcriptional co-activator with PDZ-binding motif (TAZ) for a better understanding of the underlying mechanism of tumor progression in CRC, which may provide an emerging biomarker for diagnosis and treatment of CRC. We measured the expression levels of miR-125 in CRC tissues, adjacent tissues, and cell lines (e.g. HCT116, SW480, FHC) by quantitative real-time polymerase chain reaction (qRT-PCR). The effect of miR-125 on proliferation and invasion in CRC cells was detected by Cell Counting Kit-8 (CCK-8), clone formation assay, and transwell assay. Western blotting and qRT-PCR were used to investigate the expression of TAZ after knocking down miR-125 in HCT116 cells or overexpressing miR-125 in SW480 cells. MiR-125 was significantly down-regulated in CRC compared with pericarcinomatous tissue from 18 patients. An miR-125 inhibitor promoted CRC cell proliferation and invasion, while miR-125 mimic had the opposite effect. Moreover, we found that TAZ was an miR-125 target and the siRNA knockdown of TAZ could reverse the effect of the miR-125 inhibitor on proliferation and invasion in HCT116 cells. The present study shows that miR-125 suppresses CRC proliferation and invasion by targeting TAZ.