Multiple endocrine neoplasia-type 1 (MEN1) is an autosomal dominant familial cancer syndrome characterized by tumors in parathyroids, enteropancreatic endocrine tissues, and the anterior pituitary. DNA sequencing from a previously identified minimal interval on chromosome 11q13 identified several candidate genes, one of which contained 12 different frameshift, nonsense, missense, and in-frame deletion mutations in 14 probands from 15 families. The MEN1 gene contains 10 exons and encodes a ubiquitously expressed 2.8-kilobase transcript. The predicted 610-amino acid protein product, termed menin, exhibits no apparent similarities to any previously known proteins. The identification of MEN1 will enable improved understanding of the mechanism of endocrine tumorigenesis and should facilitate early diagnosis.

MEN1 is a tumor suppressor gene that encodes a 610 amino acid nuclear protein (menin) of previously unknown function. Using a yeast two-hybrid screen with menin as the bait, we have identified the transcription factor JunD as a direct menin-interacting partner. Menin did not interact directly with other Jun and Fos family members. The menin-JunD interaction was confirmed in vitro and in vivo. Menin repressed transcriptional activation mediated by JunD fused to the Gal4 DNA-binding domain from a Gal4 responsive reporter, or by JunD from an AP1-responsive reporter. Several naturally occurring and clustered MEN1 missense mutations disrupted menin interaction with JunD. These observations suggest that menin's tumor suppressor function involves direct binding to JunD and inhibition of JunD activated transcription.

The MEN1 gene, mutations in which are responsible for multiple endocrine neoplasia type 1 (MEN1), encodes a 610-amino acid protein, denoted menin. The amino acid sequence of this putative tumor suppressor offers no clue to the function or subcellular location of the protein. We report herein, based on immunof luorescence, Western blotting of subcellular fractions, and epitope tagging with enhanced green f luorescent protein, that menin is located primarily in the nucleus. Enhanced green f luorescent proteintagged menin deletion constructs identify at least two independent nuclear localization signals (NLS), both located in the C-terminal fourth of the protein. Among the 68 known independent disease-associated mutations, none of the 22 missense and 3 in-frame deletions affect either of the putative NLS sequences. However, if expressed, none of the truncated menin proteins resulting from the 43 known frameshift͞ nonsense mutations would retain both the NLSs. The precise role(s) of menin in the nucleus remain to be understood.Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder in which affected individuals variably develop tumors in the parathyroids, anterior pituitary, and enteropancreatic endocrine tissue (1). Recently, we identified the gene responsible for MEN1 (2), and germ-line mutations in this gene have been described for nearly all the fifty-nine MEN1 probands reported so far (3, 4). Also, somatic mutations in the MEN1 gene have been identified in variable fractions of sporadic parathyroid adenomas, gastrinomas, insulinomas, lung carcinoids, and pituitary tumors (5-8). The nature of the mutations, which are consistent with a loss-of-function mechanism, the observation that the wild-type allele is consistently lost in tumors arising in patients with MEN1, and the observation that both alleles of the MEN1 gene are often inactivated in sporadic tumors indicate that tumorigenesis is very likely due to loss of function of the MEN1-encoded protein menin. Thus the MEN1 gene seems to be an excellent example of a classic tumor suppressor.Analysis of the predicted menin amino acid sequence does not show homology to any known protein in the database, nor does it disclose any apparent sequence motifs, providing no clues as to the function of the protein. As a first step toward elucidation of the role of menin in tumorigenesis, we have designed experiments to identify its subcellular location and demonstrate herein that the majority of the protein resides in the nucleus. At least two independent nuclear localization signals (NLSs), both located in the C-terminal fourth of the protein, have been identified by deletion analysis.