Circular RNA circRILPL1 promotes nasopharyngeal carcinoma malignant progression by activating the YAP/HIPPO signaling pathway

Abstract Background Circular RNAs (circRNAs) play an important regulatory role in the pathogenesis and progression of nasopharyngeal carcinoma (NPC), but they have not been sufficiently studied. Methods The high expression of circRILPL1 in NPC tissues was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and in situ hybridization (ISH). The migration, invasion, proliferation, and mechanical properties of NPC cells were detected using wound healing, transwell, MTT, colony formation assays, and atomic force microscopy (AFM). Nude mice models including subcutaneous transplantation, tail vein-lung metastasis, and footpad-lymph node metastasis were established to determine the tumor-promoting effect of circRILPL1 in vivo. The proteomic analysis of circRILPL1 was performed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The interaction of circRILPL1 with ROCK1 and IPO7 was verified through RNA pull-down, RNA immunoprecipitation (RIP) and immunofluorescence-fluorescence in situ hybridization (IF-FISH). The expression of the HIPPO pathway-related proteins was examined using western blotting. The nucleocytoplasmic distribution of YAP was analyzed by immunofluorescence and cytosolic/nuclear fractionation. The transcriptional activity of YAP was detected by luciferase reporter assay. The effect of circRILPL1 on the enrichment of YAP on CAPN2 and PXN promoters was examined by chromatin immunoprecipitation. Results We revealed for the first time that circRILPL1 was up-regulated in NPC, weakened adhesion and decreased stiffness of NPC cells, and promoted NPC proliferation and metastasis in vitro and in vivo. Mechanistically, circRILPL1 inhibited the LATS1-YAP kinase cascade by binding to and activating ROCK1, resulting in decrease of YAP phosphorylation and degradation. Binding to and cooperating with transport receptor IPO7, circRILPL1 promoted the translocation of YAP from the cytoplasm to the nucleus, where YAP promoted the transcription of cytoskeleton remodeling genes CAPN2 and PXN. By which, circRILPL1 contributed to the pathogenesis of NPC. Conclusions Our results demonstrated that circRILPL1 promoted the proliferation and metastasis of NPC through activating the YAP/HIPPO signaling pathway by binding to both ROCK1 and IPO7. Highly expressed circRILPL1 in NPC may serve as an important biomarker for tumor diagnosis and also may be a potential therapeutic target.