Peptidyl arginine deiminase 4 (PADI4), an enzyme that converts arginine residues to citrulline residues in the presence of calcium ions, affects the biochemical activities of proteins. The biological function of PADI4 as well as its mechanism in nasopharyngeal carcinoma (NPC) necessitates further investigation. PADI4 expression in NPC tissues and cells was detected using Western blot. qRT-PCR was used to determine the expression of miR-335-5p and PADI4 mRNA in NPC tissues and cells. BrdU assay and CCK-8 assay were employed to detect cell proliferation. Cell migration and invasion were evaluated using Transwell assay. NPC cells were exposed to different doses of radiation in vitro, and then colony formation assays were used to detect colony survival. The target relationship between miR-335-5p and PADI4 was verified using Western blot, qRT-PCR, and dual-luciferase reporter gene assays. Compared with normal mucosal epithelial tissues and cell lines, the expression level of PADI4 in NPC tissues and cells was significantly up-regulated. PADI4 overexpression promoted the proliferation, migration, and invasion of NPC cells. Under radiation, NPC cell survival was significantly promoted by the up-regulation of PADI4. Conversely, knock-down of PADI4 suppressed the above-mentioned malignant phenotypes. MiR-335-5p could bind with the 3' UTR of PADI4 mRNA, and suppressed the expression of PADI4. PADI4 down-regulated the expression of p21 and activated the mTOR signaling pathway. PADI4, which is negatively regulated by miR-335-5p, promotes the proliferation, migration, invasion and radioresistance of NPC cells by regulating the p21 and mTOR signaling pathways.
Keywords: NPC; PADI4; miR-335-5p.
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