PO-371 Contribution of elevated miR-146b-5p to papillary thyroid cancer diagnosis and development

Introduction Papillary thyroid carcinoma (PTC) represents 80% of thyroid cancers and ranks among the five most common cancers in many countries including Kuwait. MicroRNAs (miRNAs) are endogenous non-coding RNAs that contribute to the pathogenesis of multiple cancers by interfering with many biological processes. PTC specific miRNAs can have clinical utility as diagnostic and prognostic markers or targets to manipulate the progression of the disease. This study aimed to investigate the diagnostic potential and the biological function of miR-146 in PTC development. Material and methods The expression of miR-146b-5p was assessed by Quantitative real time PCR in different variants of PTC (113 samples), 20 cases of benign thyroid tumours and 10 cases of thyroid hyperplasia. miR-146b-5p inhibitor was transfected into primary thyroid cultured cells and the activity of 10 signalling pathways were assessed by luciferase assay. The obtained results were confirmed by immunofluroscence staining and confocal microscopy. The effect of mir-146b-5p on cancer cells growth was assessed using apoptosis assay and flow cytometry. Ethical approval to conduct this study was obtained from Kuwait Ministry of Health and Kuwait University Health Sciences Centre ethics committee. Results and discussions The real time PCR results followed by analysis with the Receiver operating characteristic curve showed that miR-146b-5p significantly discriminates classic PTC from other PTC variants and benign tumours (86% sensitivity and 73% specificity). Inhibition of miR- 146b-5p activated the JNK/AP1 pathway and increased the number of apoptotic cells. Active Phospho-JNK was detected by immunofluorescence in the nuclei of tumour cells in PTC cases with low miR-146b-5p level but not detected in tissues with high miR-146b-5p. These results confirm that miR-146b-5p inhibits activation of the JNK/AP1 pathway in vitro and in vivo . Considering the importance of the JNK pathway in facilitating the stress mediated cell death, inhibition of this pathway can be an attempt of the cancer cells to overcome the stress response and maintain survival. Conclusion high level of miR-146b-5p distinctively characterises classic PTC. miRNA-146b-5p contributes to PTC carcinogenesis by regulating the stress kinase pathway in thyroid cells.