Endocrine Abstracts

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterised by the combined occurrence of parathyroid tumours, and neuroendocrine tumours (NETs) of the pancreas and pituitary. Reliable biomarkers, ideally in plasma or serum, for the early detection and recurrence of MEN-1 associated tumours, and especially pancreatic NETs are required, and we explored the potential use of microRNAS (miRNAs), which are small non-coding RNAs that bind target mRNAs to negatively regulate gene translation, and are released from tumour cells into the circulation. We used Illumina miRNA sequencing to study miRNA expression in sera from four MEN1 patients (all with pancreatic NETs and parathyroid adenomas, and one also had a prolactinoma), and 4 control, gender-matched unaffected relatives. In total 45 miRNAs were up-regulated and 39 down-regulated (>1.5 fold-change) in all MEN1 patients when compared to controls. The most highly down-regulated (by 12-fold) miRNA, miR-3156-5p, was further investigated by treating human NET cells (BON-1 cells which are derived from a metastatic pancreatic carcinoid) with a specific miR-3156-5p inhibitor and mimic, and by studying the effects on expression of its predicted target gene, mortality factor 4-like protein 2 (MORF4L2, encoding MORF4L2), whose circulating transcripts have been reported to be correlated with NET disease progression. MORF4L2 mRNA expression, assessed using quantitative real-time PCR, was similar in control untransfected cells and in cells transfected with inhibitor or mimic. However, MORF4L2 protein translation, assessed by Western blot analysis, was significantly higher (twofold, P<0.05) and lower (52% reduction, P<0.05) after miR3156-5p inhibitor and mimic transfection, respectively, when compared to control untransfected cells. Thus, our results demonstrate that miR-3156-5p regulates MORF2L2 protein expression, and that miR3156-5p is down-regulated in the serum of MEN1 patients, thereby indicating that miR-3156-5p, in combination with its target MORF4L2, may provide a novel biomarker for MEN1-associated tumours.