Cancer Susceptibility Candidate 9 (CASC9) Promotes Colorectal Cancer Carcinogenesis via mTOR-Dependent Autophagy and Epithelial–Mesenchymal Transition Pathways

Abstract

BackgroundColorectal cancer (CRC) is the third most common cancer worldwide. Many recent studies have demonstrated that different long non-coding RNAs (lncRNAs) are involved in the initiation, advancement, and metastasis of many cancers including CRC. Cancer susceptibility candidate 9 (CASC9) is an lncRNA that has been reported in many cancers, but its role in CRC is poorly understood. In this study, we aimed to examine the expression of CASC9 in CRC cell lines and to determine the mechanism of action of CASC9 in CRC carcinogenesis.MethodsThe expression of CASC9 in CRC tissues was compared with normal samples from publicly available datasets in The Cancer Genome Atlas (TCGA) and The Encyclopedia of RNA Interactomes (ENCORI). CASC9 expression was further verified in four CRC cell lines (DLD1, HT-29, SW480, and HCT-116) and normal colorectal cell line (CCD-112CoN) by real-time quantitative polymerase chain reaction (RT-qPCR). After gene silencing in HCT-116 and SW480, Cell Counting Kit-8 assay, clonogenic assay, and wound healing assay were performed to evaluate cell proliferation, viability, and migration index of cells. Western blotting was used to explore the key pathways involved.ResultsCASC9 was significantly upregulated as analyzed from both public datasets TCGA and ENCORI where its overexpression was associated with poor survival of CRC patients. Similarly, CASC9 was significantly overexpressed in the CRC cell lines compared with normal cells studied. The silencing of CASC9 in HCT-116 and SW480 attenuated cell proliferation and migration significantly. Furthermore, pathways investigations showed that silencing of CASC9 significantly induced autophagy, promoted AMP-activated protein kinase (AMPK) phosphorylation, inhibited mTOR and AKT signaling pathways, and altered epithelial–mesenchymal transition (EMT) marker protein expression.ConclusionWe demonstrated that silencing of CASC9 contributes to the reduced CRC cell proliferation and migration by regulating autophagy and AKT/mTOR/EMT signaling. Therefore, CASC9 plays an important role in carcinogenesis, and its expression may act as a prognostic biomarker and a potential therapeutic target of CRC management.

Potential of antiviral drug oseltamivir for the treatment of liver cancer

“…A variety of studies have revealed that autophagy promotes cancer cell death in early phases and survival in later phases ( 18 - 20 ). Autophagy may provide energy for excessive cancer cell proliferation or lead to the insufficient availability of nutrients for cancer cells by disrupting energy homeostasis, thus causing cell death ( 21 ). A previous study reported that quinacrine-induced autophagy in ovarian cancer cells leads to excessive autophagic flux and promotes cell death ( 22 ).…”

Suppression of small nucleolar RNA host gene 8 (SNHG8) inhibits the progression of colorectal cancer cells

“…Western blotting was performed using standard, established protocol as previously published [ 9 ]. Briefly, protein isolation was performed using RIPA lysis and extraction buffer (Thermo Fisher Scientific, United States) with a supplement of cOmplete ULTRA Tablets, Mini EDTA-free, Easy pack Protease Inhibitor Cocktail (Roche, Switzerland).…”

“…In addition to that, many studies have reported the central role of lncRNAs in CRC including, initiation, progression, metastasis, and drug resistance process of CRC. For example, our team has reported that upregulation of CASC9 and RAMS11 promotes CRC carcinogenesis through suppression of mTOR-dependent autophagy, apoptosis, and initiating epithelial to mesenchymal transition (EMT) [ 2 , 9 ]. Another study demonstrated that higher RAMS11 expression accelerates resistance to topoisomerase inhibitors chemotherapy via chromobox protein 4 mediated activation of topoisomerase II alpha [ 7 ].…”

Autophagy: A Versatile Player in the Progression of Colorectal Cancer and Drug Resistance

“…Autophagy activation was found to attenuate the migration of CRC cells ( 100 ). Yet another study reported that Beclin 1 overexpression prevented invasion and migration of aggressive CRC cells suggesting autophagy activation may reverse the aggressive cancers ( 55 ).…”