Long non-coding RNA CASC9 promotes the progression and development of gastric cancer via regulating miR-370/EGFR axis.

lncRNA cancer susceptibility 9 (CASC9) is a pivotal modulator in various cancers, such as colorectal cancer, breast cancer and esophageal cancer. However, its exact role in gastric cancer (GC) has not been systematically studied. Here, using a combination of molecular and cell biology approaches, we found that CASC9 also acts as a factor promoting the progression of GC. First, mRNA and protein expression levels were quantified by real-time quantitative reverse transcription PCR (qRT-PCR) and western blot, respectively. Second, CCK-8 assay, colony formation assay and cell cycle analysis were performed to compare the cell growth abilities when CASC9 was knocked down. Third, the proliferative cells were determined by labeling Edu and the regulatory effect of CASC9 on miR-370 was detected by RNA-protein pull-down and luciferase reporter assays. Finally, in vivo mice model was established to verify the role of CASC9 in promoting GC progression. Our results showed that CASC9 was up-regulated significantly in both GC tissues and cell lines. Conversely, CASC9 knockdown inhibited GC growth in vitro. Further analysis indicated that CASC9 directly targeted miR-370 and negatively regulated miR-370 expression in GC. Besides, EGFR (epidermal growth factor receptor) was identified as a direct target gene of miR-370. Taken together our results support a model in which CASC9 promotes GC progression through miR-370/EGFR/ERK/AKT pathway. Finally, in vivo CASC9 knockdown resulted in impaired GC growth. In sum, this study firstly demonstrates that lncRNA CASC9 acts as an oncogene through altering EGFR expression level via negatively regulating miR-370 expression.