Abstract
Increasing evidence has shown that dysregulation of mircoRNA (miRNA) is linked to the development and progression of human cancer, including gastric cancer (GC). In the current study, by analysing the GEO database (GSE78091), we found that miR-660 was significantly downregulated in GC. Consistently, quantitative real-time PCR (qRT-PCR) results showed that miR-660 was dramatically decreased in GC tissues and cell lines. Importantly, low miR-660 expression was closely related to larger tumor size (P = 0.008), lymph node metastasis (P = 0.006), advanced TNM stage (P = 0.029), and poor outcome (P = 0.023). Ectopic expression of miR-660 inhibited proliferation of MGC-803 and AGS cells and induced apoptosis. Further mechanism experiments suggested that the well-known oncogene E2F3 (E2F transcription factor 3) was a downstream target of miR-660. Overexpression of miR-660 reduced the activity of E2F3 by directly binding to the 3221˜3226 region of E2F3 3`-UTR, and there was a strong negative correlation between the expression of miR-660 and E2F3 in GC tissues (r = - 0.648, P < 0.001). Furthermore, E2F3 overexpression abrogated the anti-proliferation effect of miR-660 in GC cell lines. Of note, we found an N6-methyladenosine (m6A) motif at the 3063˜3067 region of E2F3 3`-UTR, and this m6A-modified motif was required for the interaction between miR-660 and E2F3 3`-UTR. Collectively, our findings reveal the compelling role of m6A in GC and highlight the regulatory function of the miR-660/E2F3 pathway in GC progression.