Objective: Circular RNA is a type of endogenous RNA molecule with a stable closed-loop structure which is ubiquitous in mammals. Circular RNA HIPK3 (circHIPK3) is highly expressed in hepatocellular carcinoma and promotes the growth of hepatoma cells. However, its role in prostate cancer (PCa) has not been reported. This study aims to explore whether circHIPK3 could affect the proliferative and invasive potentials of PCa cells by regulating miRNA-338-3p. Methods: Expression levels of circHIPK3 and miRNA-338-3p in PCa tissues and cells were determined by RT-qPCR. The regulatory effects of circHIPK3 and miRNA-338-3p on proliferative and invasive potentials of PCa cells were evaluated by CCK-8 and transwell assay, respectively. We verified the binding between miRNA-338-3p and ADAM17, as well as miRNA-338-3p and circHIPK3 through dual-luciferase reporter gene assay. Rescue experiments were conducted to clarify whether circHIPK3 affected the proliferative and invasive potentials of PCa cells by regulating miRNA-338-3p. Results: Expression level of circHIPK3 in PCa tissues was remarkably higher than that of paracancerous tissues. Knockdown of circHIPK3 inhibited the proliferative and invasive rates of PC-3 and DU145 cells. Dual-luciferase reporter gene assay indicated that circHIPK3 could bind to miRNA-338-3p. Moreover, miRNA-338-3p expression was downregulated in PCa tissues. miRNA-338-3p expression was negatively correlated with lymph node metastasis and distant metastasis. miRNA-338-3p overexpression markedly reduced proliferative and invasive abilities of PC-3 and DU145 cells. Furthermore, ADAM17 was confirmed to be the target gene of miRNA-338-3p. Overexpression of ADAM17 enhanced proliferative and invasive abilities of PC-3 and DU145 cells. Finally, rescue experiments indicated that miRNA-338-3p knockdown in PC-3 and DU145 cells partially reversed the regulatory effects of circHIPK3 on proliferative and invasive potentials. Conclusion: Overexpression of circHIPK3 promotes the proliferative and invasive potentials of PCa cells through sponging miRNA-338-3p to regulate ADAM17 expression, thus accelerating the malignant progression of PCa.

Metastasis is a hallmark of malignant neuroblastoma and is the main reason for therapeutic failure and recurrence of the tumor. The CXC chemokine receptor-4 (CXCR4), a Gi protein-coupled receptor for the ligand CXCL12/stromal cell-derived factor-1α (SDF-1α), is expressed in various types of tumor. This receptor mediates the homing of tumor cells to specific organs that express the ligand, CXCL12, for this receptor and plays an important role in tumor growth, invasion, metastasis and angiogenesis. In the present study, the inflammatory cytokine, tumor necrosis factor-α (TNF-α) upregulated CXCR4 expression in neuroblastoma cells and increased migration to the CXCR4 ligand SDF-1α. In addition, this effect was dependent upon NF-κB transcriptional activity, as blocking the NF-κB pathway with pyrrolidinedithiocarbamic acid ammonium salt suppressed TNF-α-induced upregulation of CXCR4 expression and reduced the migration towards the CXCR4 ligand, SDF-1α. Treating neuroblastoma cells with TNF-α resulted in the activation of nuclear factor-kappa B (NF-κB) and subsequently, the translocation of NF-κB from the cytoplasm to the nucleus. Using immunohistochemistry, NF-κB and CXCR4 were significantly correlated with each other (P=0.0052, Fisher’s exact test) in a cohort of neuroblastoma samples (n=80). The present study indicates that the inflammatory cytokine, TNF-α, partially functions through the NF-κB signaling pathway to upregulate CXCR4 expression to foster neuroblastoma cell metastasis. These findings indicate that effective inhibition of neuroblastoma metastasis should be directed against the inflammatory cytokine-induced NF-κB/CXCR4/SDF-1α signaling pathway.

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BackgroundAccumulating evidence implicates the transcription factor NF-κB as a positive mediator of tumor metastasis, but the molecular mechanism(s) involved in this process remains largely unknown. In this study, we investigated the role of NF-κB signaling pathway in the regulation of CXC chemokine receptor-4 (CXCR4) in neuroblastoma metastasis.Material/MethodsNF-κB, CXCR4 mRNA and protein expression were measured by RT-PCR, and Western blot. Tumor necrosis factor-a (TNF-α) was used to induce the upregulation of NF-κB and CXCR4. The knockdown of NF-κB and CXCR4 was achieved by PDTC. Transwell assay was used to investigate the role of NF-κB (P65) in neuroblastoma cell migration and invasion. An in vitro co-culture system was established to investigate the role of tumor microenvironment in regulation of the NF-κB signaling pathway.ResultsOver-expression of NF-κB (p65) promoted tumor migration and invasion through the upregulation of CXCR4; however, knockdown of NF-κB(P65) inhibited tumor migration and invasion through blocking the expression of CXCR4. Consistently, in the co-culture system, the expression of CXCR4 was partly dependent on the expression of NF-κB (p65).ConclusionsOur studies reveal critical roles for the NF-κB signaling pathway in neuroblastoma migration and invasion. The mechanism may be through up-regulation of CXCR4, mediated by the NF-κB signaling pathways. Targeting NF-κB signalling pathways and ultimately CXCR4 could be a strategy in neuroblastoma therapy.