Epigenetic regulation of the long non-coding RNA Meg3 by the tumor suppressor menin

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 303-321-Cancer in Endocrine Tissues
Bench to Bedside
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-313
Sita D Modali*1, Shruti S Desai2, Vaishali I Parekh3 and Sunita K Agarwal4
1National Institute of Diabetes and Digestive and Kidney Diseases,NIH, Bethesda, MD, 2National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD, 3NIH, Bethesda, MD, 4NIDDK/NIH, Bethesda, MD
The multiple endocrine neoplasia type 1 (MEN1) syndrome is characterized by the co-occurrence of hormone-secreting tumors in multiple endocrine glands, mainly the parathyroids, anterior pituitary, and endocrine pancreas. Germline heterozygous mutations in the MEN1 gene predispose to tumor formation in specific endocrine (and some non-endocrine) tissues. Tumors show bi-allelic loss of the MEN1 gene. Also, 2-30 % of sporadic tumors of the types observed in MEN1 are caused by somatic mutations in this gene. The MEN1 gene encodes a tumor suppressor protein menin, a component of MLL1- or MLL2-containing histone methyltransferase complexes that trimethylate histone H3 at lysine 4 (H3K4me3). ChIP-seq and gene expression analysis of mouse embryonic stem cells have shown that, loss of menin results in significant loss of H3K4me3 and reduced expression of Meg3 (maternally expressed gene 3 that encodes a large non-coding RNA). This lead to the hypothesis that Meg3 could be an epigenetically-regulated downstream target of menin. In this study, we elucidated the effect of menin on Meg3 expression in endocrine cells to understand the mechanism by which menin regulates Meg3 for the pathogenesis of endocrine tumors. Transient or stable expression of menin was performed in a mouse insulinoma cell line (MIN6); the cell proliferation rate and Meg3 expression levels were assessed. Flow cytometry and cell counting analysis showed that transient expression of menin did not effect proliferation but stable expression significantly reduced cell proliferation. In both transient and stably-transfected cells, RT-PCR analysis showed that Meg3 levels increased with ectopic menin expression. This effect was more pronounced in stable menin expressing cells emphasizing a possibility that activation of Meg3 expression by menin requires multiple cell divisions to acquire active epigenetic modifications (H3K4me3) or to erase epigenetic modifications that inactivate gene expression (DNA methylation). Therefore, we propose that menin loss in tumors would lead to decreased H3K4me3 or increased DNA methylation at the MEG3 locus. Future studies in cell lines and tumors to investigate these aspects will provide mechanistic insights. Overall, our results have important implications for menin-mediated chromatin reorganization and DNA methylation at the MEG3 locus in the pathogenesis of endocrine tumors.

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