MicroRNA deregulation and pathway alterations in nasopharyngeal carcinoma

MicroRNAs (miRNAs) are a family of small non-coding RNA molecules of about 20–23 nucleotides in length, which negatively regulate protein-coding genes at post-transcriptional level. Using a stem-loop real-time-PCR method, we quantified the expression levels of 270 human miRNAs in 13 nasopharyngeal carcinoma (NPC) samples and 9 adjacent normal tissues, and identified 35 miRNAs whose expression levels were significantly altered in NPC samples. Several known oncogenic miRNAs, including miR-17-92 cluster and miR-155, are among the miRNAs upregulated in NPC. Tumour suppressive miRNAs, including miR-34 family, miR-143, and miR-145, are significantly downregulated in NPC. To explore the roles of these dysregulated miRNAs in the pathogenesis of NPC, a computational analysis was performed to predict the pathways collectively targeted by the 22 significantly downregulated miRNAs. Several biological pathways that are well characterised in cancer are significantly targeted by the downregulated miRNAs. These pathways include TGF-Wnt pathways, G1-S cell cycle progression, VEGF signalling pathway, apoptosis and survival pathways, and IP3 signalling pathways. Expression levels of several predicted target genes in G1-S progression and VEGF signalling pathways were elevated in NPC tissues and showed inverse correlation with the down-modulated miRNAs. These results indicate that these downregulated miRNAs coordinately regulate several oncogenic pathways in NPC.