PVT1 Mediates Cell Proliferation, Apoptosis and Radioresistance in Nasopharyngeal Carcinoma Through Regulating miR-515-5p/PIK3CA Axis.

Abstract

BackgroundRadioresistance greatly hinders the treatment of nasopharyngeal carcinoma (NPC). Long noncoding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) has been corroborated to participate in diverse cancers, including NPC. Our aim was to investigate the underlying molecular mechanism of PVT1 in NPC radioresistance.MethodsQuantitative real-time polymerase chain reaction (qRT-PCR) was utilized to measure the expression levels of PVT1, microRNA (miR)-515-5p and phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) in NPC tissues and cells. Cell counting kit-8 (CCK8) assay, colony formation assay and flow cytometry assay were employed to detect cell proliferation, radiosensitivity and apoptosis, respectively. The protein levels of Cyclin D1, B-cell lymphoma 2 associated X (Bax), Cleaved-caspase-3, PIK3CA, protein kinase B (AKT) and phosphorylated AKT (p-AKT) in samples were measured by Western blot. The starBase was used to predict the binding sites between miR-515-5p and PVT1 or PIK3CA. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were performed to verify the interaction. Xenograft tumor model was established to investigate the biological role of PVT1 in vivo.ResultsThe levels of PVT1 and PIK3CA were upregulated in NPC tissues and cells, opposite to the expression of miR-515-5p. Knockdown of PVT1 inhibited cell proliferation, radioresistance and promoted cell apoptosis in NPC cells. Meanwhile, PVT1 silencing downregulated Cyclin D1, and upregulated Bax and Cleaved-casp-3 in NPC cells after radiotherapy. Besides, miR-515-5p interacted with PVT1 and targeted PIK3CA in NPC cells. Further studies indicated that PVT1 regulated radioresistance via miR-515-5p/PIK3CA axis and modulated the AKT pathway by interacting with miR-515-5p. Moreover, knockdown of PVT1 suppressed tumor growth in vivo.ConclusionDownregulation of PVT1 inhibited proliferation, radioresistance and promoted apoptosis by downregulating PIK3CA via sponging miR-515-5p in NPC cells.