Menin, a tumor suppressor, associates with nonmuscle myosin II-A heavy chain.

MEN1 is a likely tumor suppressor gene that encodes a novel protein, menin. Menin is a 610 amino-acid residue protein with as yet unknown function(s). We have used tandem affinity purification and mass spectroscopy to isolate and identify proteins associating with menin from cultured HeLa cell extracts. This strategy has resulted in the isolation and identification of nonmuscle myosin type II-A heavy chain (NMHC II-A) as a menin interacting protein. This interaction was confirmed by glutathione-S-transferase pulldown assays, by coimmunoprecipitation, and by actin selection of myosin. We have further identified the amino-terminal region of menin and the head domain of NMHC II-A to be regions required for this interaction. Moreover menin was seen to colocalize with this myosin isoform in the cleavage furrow of dividing cells by indirect immunofluoresence. These data indicate that menin through binding to NMHC II-A could participate in cell division and in other processes that involve NMHC II-A.

Molecular pathology of the MEN1 gene.

Multiple endocrine neoplasia type 1 (MEN1), among all syndromes, causes tumors in the highest number of tissue types. Most of the tumors are hormone producing (e.g., parathyroid, enteropancreatic endocrine, anterior pituitary) but some are not (e.g., angiofibroma). MEN1 tumors are multiple for organ type, for regions of a discontinuous organ, and for subregions of a continuous organ. Cancer contributes to late mortality; there is no effective prevention or cure for MEN1 cancers. Morbidities are more frequent from benign than malignant tumor, and both are indicators for screening. Onset age is usually earlier in a tumor type of MEN1 than of nonhereditary cases. Broad trends contrast with those in nonneoplastic excess of hormones (e.g., persistent hyperinsulinemic hypoglycemia of infancy). Most germline or somatic mutations in the MEN1 gene predict truncation or absence of encoded menin. Similarly, 11q13 loss of heterozygosity in tumors predicts inactivation of the other MEN1 copy. MEN1 somatic mutation is prevalent in nonhereditary, MEN1-like tumor types. Compiled germline and somatic mutations show almost no genotype/phenotype relation. Normal menin is 67 kDa, widespread, and mainly nuclear. It may partner with junD, NF-kB, PEM, SMAD3, RPA2, FANCD2, NM23beta, nonmuscle myosin heavy chain II-A, GFAP, and/or vimentin. These partners have not clarified menin's pathways in normal or tumor tissues. Animal models have opened approaches to menin pathways. Local overexpression of menin in Drosophila reveals its interaction with the jun-kinase pathway. The Men1+/- mouse has robust MEN1; its most important difference from human MEN1 is marked hyperplasia of pancreatic islets, a tumor precursor stage.