BackgroundThe advantages and utility of microRNAs (miRNAs) as diagnostic and prognostic cancer markers is at the vanguard in recent years. In this study, we attempted to identify and validate the differential expression of miRNAs in oral squamous cell carcinoma (OSCC), to correlate their expression with the clinico-pathological profile of tumours and to identify the signaling pathways through which the aberrantly expressed miRNAs effect tumourigenesis.MethodsmiRCURY LNA™ array with probes specific to 1168 miRNAs and TaqMan assays specific for 10 miRNAs was employed to evaluate and validate miRNA expression in a discovery cohort (n = 29) and validation cohort (n = 61) of primary OSCC tissue specimens, respectively. A computational pipeline with sequential integration of data from miRTarBase, CytoScape, UniProtKB and DIANA-miRPath was utilized to map the target genes of deregulated miRNAs and associated molecular pathways.ResultsMicroarray profiling identified 46 miRNAs that were differentially expressed in OSCC. Unsupervised clustering demonstrated a high degree of molecular heterogeneity across the tumour samples as the clusters did not represent any of their clinico-pathological characteristics. The differential expression of 10 miRNAs were validated by RT-qPCR (let-7a, let-7d, let-7f and miR-16 were downregulated while miR-29b, miR-142-3p, miR-144, miR-203, and miR-223 were upregulated in OSCC; the expression of miR-1275 was variable in tumours, with high levels associated to regional lymph node invasion; additionally, miR-223 exhibited an association with advanced tumour stage/size). In silico analyses of the experimentally confirmed target genes of miRNAs revamp the relationship of upregulated miRNAs with tumour suppressor genes and of downregulated miRNAs with oncogenes. Further, the differentially expressed miRNAs may play a role by simultaneously activating genes of PI3K/Akt signaling on one hand and by repressing genes of p53 signaling pathway on the other.ConclusionsThe identified differentially expressed miRNAs and signaling pathways deregulated in OSCC have implications for the development of novel therapeutic strategies. To the best of our knowledge, this is the first report to show the association of miR-1275 with nodal invasion and the upregulation of miR-144 in OSCC.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-016-0512-8) contains supplementary material, which is available to authorized users.

Oral squamous cell carcinoma is the most aggressive cancer that is associated with high recurrence, metastasis, and poor treatment outcome. Dysregulation of long non-coding RNAs has been shown to promote tumor growth and metastasis in several cancers. In this study, we investigated the expression of 11 selected long non-coding RNAs that are associated with cell proliferation, metastasis, and tumor suppression in oral squamous cell carcinomas and normal tissues by quantitative real-time polymerase chain reaction. Out of the 11 long non-coding RNAs profiled, 9 were significantly overexpressed in tumors with tobacco chewing history. Moreover, the long non-coding RNA profile was similar to the head and neck cancer datasets of The Cancer Genome Atlas database. Linc-RoR, a regulator of reprogramming, implicated in tumorigenesis was found to be overexpressed in undifferentiated tumors and showed strong association with tumor recurrence and poor therapeutic response. In oral squamous cell carcinomas, for the first time, we observed linc-RoR overexpression, downregulation of miR-145-5p, and overexpression of c-Myc, Klf4, Oct4, and Sox2, suggesting the existence of linc-RoR-mediated competing endogenous RNA network in undifferentiated tumors. Taken together, this study demonstrated the association of linc-RoR overexpression in undifferentiated oral tumors and its prognostic value to predict the therapeutic response.

Our results corroborate the previous findings on the overexpression of mir-21 and downregulation of miR-138 in OSCC. As the expression of miR-184 is controversial in tongue/oral cancer, the downregulation may be specific to tumor anatomical localization. On the other hand, to the best of our knowledge, this is the first report to show the association of miR-155 with tobacco chewing and the downregulation of miR-125b-2* in OSCC. Computational predictions suggest that miR-125b-2* may have a role in alternative splicing.