Epigenetic regulation is emerging as a key feature in the molecular characteristics of various human diseases. Epigenetic aberrations can occur from mutations in genes associated with epigenetic regulation, improper deposition, removal or reading of histone modifications, DNA methylation/demethylation and impaired non-coding RNA interactions in chromatin. Menin, the protein product of the gene causative for the multiple endocrine neoplasia type 1 (MEN1) syndrome, interacts with chromatin-associated protein complexes and also regulates some non-coding RNAs, thus participating in epigenetic control mechanisms. Germline inactivating mutations in the MEN1 gene that encodes menin predispose patients to develop endocrine tumors of the parathyroids, anterior pituitary and the duodenopancreatic neuroendocrine tissues. Therefore, functional loss of menin in the various MEN1-associated endocrine cell types can result in epigenetic changes that promote tumorigenesis. Because epigenetic changes are reversible, they can be targeted to develop therapeutics for restoring the tumor epigenome to the normal state. Irrespective of whether epigenetic alterations are the cause or consequence of the tumorigenesis process, targeting the endocrine tumor-associated epigenome offers opportunities for exploring therapeutic options. This review presents epigenetic control mechanisms relevant to the interactions and targets of menin, and the contribution of epigenetics in the tumorigenesis of endocrine cell types from menin loss.
Sucharitha Iyer and Sunita K Agarwal
Maya Elena Lee, Aisha Aderayo Tepede, Adel Mandl, Lee Scott Weinstein, Jaydira del Rivero, Sunita K Agarwal and Jenny E. Blau
Gastroenteropancreatic (GEP) neuroendocrine tumors (NETs) comprise a heterogenous and diverse group of neoplasms arising from a common neuroendocrine cell origin. The majority of these tumors occur sporadically while ~20% manifest within the context of hereditary syndromes. Germline MEN1 mutations cause a syndrome with an increased susceptibility to multifocal primary GEP NETs. In addition, MEN1 mutations also occur in sporadic GEP NETs. MEN1 alternations are the most frequent sporadic mutation found in pancreatic neuroendocrine tumors (PNETs). We explore the implication of the loss of the MEN1 encoded protein menin as a key pathogenic driver in subsets of GEP NETs with downstream consequences including upregulation of the oncogenic receptor c-MET (hepatocyte growth factor receptor). This review will summarize the data related to the clinical presentation, therapeutic standards, and outcomes of sporadic and MEN1 associated GEP NETs. We present the data on c-MET expression in GEP NETs, clinical trials using c-MET inhibtors, and provide an overview of the molecular mechanisms by which c-MET inhibition in GEP NETs represents a potential precision-medicine targeted approach.