RORβ suppresses the stemness of gastric cancer cells by downregulating the activity of the Wnt signaling pathway

Gastric cancer (GC) is the third leading cause of cancer-related mortality and the fifth most common type of cancer worldwide. GC stem cells (GCSCs) have been reported to be responsible for the malignant behavior of GC. However, the key molecular mechanism controlling GCSC function remains unclear. The present study aimed to investigate the function of retinoic acid-related orphan receptor β (RORβ) in GC. The expression levels of RORβ in GC cells and clinical GC tissues were analyzed using western blotting, reverse transcription-quantitative PCR (RT-qPCR) and immunohistochemistry. The association between RORβ expression levels and GCSC markers was analyzed using Gene Set Enrichment Analysis, and GeneChip was performed to identify differentially expressed genes between control and RORβ-overexpressing GC cells. CCK-8 and flow cytometric assays were used to evaluate the effect of RORβ on cell viability and apoptosis, respectively. The effect of RORβ on the self-renewal capacity of GCSCs was measured using a sphere formation assay, the expression levels of induced pluripotent stem (iPS) factors and epithelial-mesenchymal transition (EMT)-related factors were measured by RT-qPCR and western blotting, and the tumorigenic capacity was measured by an in vivo mouse model. Finally, the impact of RORβ on the Wnt signaling pathway was determined using western blotting and a TOP/FOP flash assay. The results revealed that the expression levels of RORβ were downregulated in GC tissues compared with para-carcinoma tissues, and were inversely associated with the expression levels of GCSC markers. The overexpression of RORβ upregulated the expression levels of the pro-apoptotic gene, Bcl-2 like protein 11, which subsequently inhibited the viability and promoted the apoptosis of GC cells. In addition, RORβ decreased the sphere forming ability, and downregulated the expression levels of iPS cell- and EMT-related factors. In vivo, RORβ suppressed the tumorigenic capacity and stemness of GC cells. Mechanistically, RORβ was revealed to decrease the activity of the Wnt/β-catenin signaling pathway in GCSCs. In conclusion, the findings of the present study identified RORβ as a novel suppressor of GCSCs and highlighted the prospect of RORβ as a novel candidate target for stem cell-based GC therapy.