Long Non-Coding RNA Cancer Susceptibility 9 (CASC9) Up-Regulates the Expression of ERBB2 by Inhibiting miR-193a-5p in Colorectal Cancer

BACKGROUND: Emerging studies have reported that long non-coding RNAs (lncRNAs) were crucial regulators in the progression of colorectal cancer (CRC). LncRNA susceptibility 9 (CASC9) was involved in several cancers; however, its role in CRC remains unknown. METHODS: RT-PCR was done to probe the expression of CASC9 and miR-193a-5p in CRC samples. CRC cell lines (HCT116 and SW480) were used as cell models. The biological influence of CASC9 on cancer cells was studied using CCK-8 assay, Transwell assay and TUNEL assay in vitro, and subcutaneous xenotransplanted tumor model in vivo. Interaction between CASC9 and miR-193a-5p was investigated by bioinformatics analysis, RT-PCR, and luciferase reporter assay. The expression level of the downstream gene of miR-193a-5p, erb-b2 receptor tyrosine kinase 2 (ERBB2), was tested by Western blot. RESULTS: CASC9 was significantly up-regulated in CRC samples, while miR-193a-5p was markedly down-regulated. Overexpression of CASC9 promoted viability, migration and invasion of CRC cells, while overexpression of miR-193a-5p had the opposite effect. CASC9 could down-regulate miR-193a-5p via sponging it, and there was a negative relevancy between CASC9 and miR-193a-5p in CRC samples. CASC9 also enhanced the expression levels of ERBB2, while this effect could be reversed by co-transfection with miR-193a-5p. CONCLUSION: CASC9, an oncogenic lncRNA, was abnormally up-regulated in CRC tissues, and it could indirectly modulate the expression of ERBB2 via reducing the expression level of miR-193a-5p.