Abstract
BACKGROUND: Papillary thyroid cancer (PTC) is a malignant tumor that poses a serious threat to human health. LncRNA CASC9 serves as an oncogene in numerous tumors. The purpose of this study was to explore the mechanism of lncRNA CASC9 regulating doxorubicin (Dox) resistance in PTC. METHODS: The expression of CASC9, miR-28-3p and BCL-2 in PTC tissues or dox-resistant cells was determined by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot (WB). CCK-8, colony formation assay, flow cytometry and transwell assay were used to measure the semi-inhibitory concentration (IC50) of dox, cell proliferation, apoptosis and migration, respectively. Dual luciferase reporter gene assays were performed to verify the targeting relationship between miR-28-3p and CASC9 or BCL-2. Rescue experiments were applied to verify the mechanism of CASC9. Finally, the role of CASC9 was verified by xenograft modeling in vivo. RESULTS: We discovered that CASC9 was enhanced in PTC tissues, cells and Dox-resistant cells (BCPAP/Dox and K1/Dox). Furthermore, CASC9 inhibition markedly restrained the proliferation, migration and facilitated apoptosis of Dox cells. In vivo experiments also showed that silencing of CASC9 inhibited tumor growth. Meanwhile, knockdown of CASC9 sensitized PTC cells to Dox. CASC9 enhanced tumor progression by activating the PI3K/AKT signaling pathway. Furthermore, bioinformatics analysis identified miR-28-3p as a downstream target of CASC9. MiR-28-3p inhibitor reversed the impact of CASC9 knockdown in BCPAP/Dox and K1/Dox. Further studies showed that CASC9 positively regulated BCL-2 expression through miR-28-3p. miR-28-3p weakened Dox resistance, proliferation, migration and accelerated apoptosis of PTC cells via BCL-2. CONCLUSION: CASC9, as an oncogenic lncRNA, has a promotional effect on Dox resistance and PTC progression via miR-28-3p/BCL-2 axis and PI3K/AKT signaling pathway.