Functional inactivation of menin, encoded by the MEN1 gene, causes the inherited multiple endocrine neoplasia type 1 (MEN1) syndrome and some but not all sporadic pancreatic endocrine tumors. Therefore, unraveling molecular events upstream or downstream of menin could point to other causative genes and/or regulatory events responsible for such tumor types. Menin resides in a histone methylating protein complex that trimethylates histone H3 at lysine-4 (H3K4me3), an epigenetic mark for active gene expression. Therefore, we have determined a genome-wide map of menin-dependent H3K4me3 (using ChIP-Seq) and menin-dependent gene-expression program in wild-type (WT) and menin-null mouse embryonic stem cells (ESCs) and in pancreatic islet-like endocrine cells (PILECs), which we derived from WT and menin-null mouse ESCs through in vitro differentiation. We found menin-dependent H3K4me3 specifically targeting the Meg3 gene in mouse ESCs, and all four Hox loci in differentiated PILECs. Gene expression from the Meg3 locus and from all of the four Hox loci was abolished in menin-null cells. Both Meg3 and Hox loci have been implicated in MEN1-like sporadic tumors: MEG3 in pituitary tumors, and HOX in parathyroid tumors. Our data suggest that these genes with menin-dependent H3K4me3 could be relevant players in the tumorigenesis of endocrine cell types associated with MEN1. Furthermore, our work shows that menin-null mouse ESCs could also be differentiated in vitro into islet-like endocrine cells, underscoring the utility of menin-null ESC-derived specialized cell types for genome-wide analyses studies. Our current efforts are directed towards understanding the regulation and activity of genes at the MEG3 and HOX loci. We have shown that cyclin-dependent kinase inhibitors (CDKIs) of the INK4 family (4 genes) and the Cip/Kip family (3 genes) that negatively regulate cell cycle progression and cell proliferation have rare germline or somatic mutations in endocrine tumor states related to MEN1. Also, mouse models show an endocrine neoplasia phenotype in 'knock-in'mice homozygous for the CDK4-R24C mutation, or by the combined loss of two different CDKIs, p18 and p27. Therefore, understanding the molecular basis of CDK and CDKI regulation could provide insights into their contribution to endocrine tumorigenesis. We have investigated the contribution of cell cycle regulators in endocrine tumorigenesis, particularly mutations in CDKI genes. We are interested in investigating the molecular basis of cell cycle regulation in endocrine cells.
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