Sunita K. Agarwal

Menin Interacts with the AP1 Transcription Factor JunD and Represses JunD-Activated Transcription

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 menins tumor suppressor function involves direct binding to JunD and inhibition of JunD activated transcription.

HRPT2, encoding parafibromin, is mutated in hyperparathyroidism-jaw tumor syndrome.

We report here the identification of a gene associated with the hyperparathyroidism–jaw tumor (HPT–JT) syndrome. A single locus associated with HPT–JT (HRPT2) was previously mapped to chromosomal region 1q25–q32. We refined this region to a critical interval of 12 cM by genotyping in 26 affected kindreds. Using a positional candidate approach, we identified thirteen different heterozygous, germline, inactivating mutations in a single gene in fourteen families with HPT–JT. The proposed role of HRPT2 as a tumor suppressor was supported by mutation screening in 48 parathyroid adenomas with cystic features, which identified three somatic inactivating mutations, all located in exon 1. None of these mutations were detected in normal controls, and all were predicted to cause deficient or impaired protein function. HRPT2 is a ubiquitously expressed, evolutionarily conserved gene encoding a predicted protein of 531 amino acids, for which we propose the name parafibromin. Our findings suggest that HRPT2 is a tumor-suppressor gene, the inactivation of which is directly involved in predisposition to HPT–JT and in development of some sporadic parathyroid tumors.

The tumor suppressor protein menin interacts with NF-κB proteins and inhibits NF-κB-mediated transactivation

Multiple endocrine neoplasia type 1 is an autosomal dominant tumor syndrome. Manifestations include neoplasms of the parathyroid glands, enteropancreatic neuroendocrine cells, and the anterior pituitary gland. The MEN1 tumor suppressor gene encodes menin, a 610 amino acid nuclear protein without sequence homology to other proteins. To elucidate menin function, we used immunoprecipitation to identify interacting proteins. The NF-κB proteins p50, p52 and p65 were found to interact specifically and directly with menin in vitro and in vivo. The region of NF-κB proteins sufficient for binding to menin is the N-terminus. Furthermore, amino acids 305–381 of menin are essential for this binding. Menin represses p65-mediated transcriptional activation on NF-κB sites in a dose-dependent and specific manner. Also, PMA (phorbol 12-myristate 13-acetate)-stimulated NF-κB activation is suppressed by menin. These observations suggest that menins ability to interact with NF-κB proteins and its modulation of NF-κB transactivation contribute to menins tumor suppressor function.

Familial isolated hyperparathyroidism: clinical and genetic characteristics of 36 kindreds.

Familial hyperparathyroidism (HPT) encompasses a clinically and genetically heterogeneous group of disorders. Syndromes with familial HPT include multiple endocrine neoplasia type 1 (MEN1) (Mendelian Inheritance in Man [MIM] 1311001) (63, 87), multiple endocrine neoplasia type 2A (MEN2A) (MIM 171400)(42, 79, 86), familial hypocalciuric hypercalcemia (FHH) (MIM 145980, 145981, 600740) also known as familial benign hypercalcemia (38, 64), and the hyperparathyroidism-jaw tumor syndrome (HPT-JT; HRPT2) (MIM 145001) (45). Familial isolated hyperparathyroidism2 (FIH; HRPT1) (MIM 145000) is a subgroup of familial HPT that can result from the incomplete expression of a syndromic form of familial HPT or from full expression of other entities (Figure 1). It is unknown how many as yet unrecognized clinical entities, including mutant genotypes, can also present as FIH. MEN1 is an autosomal dominant disorder characterized by endocrine and nonendocrine tumors, most strikingly involving the parathyroids, enteropancreatic endocrine system, and pituitary. Because FIH is seen less frequently than full expressions of MEN1, because HPT is the earliest and most frequent endocrinopathy in MEN1, and because even some large families with an apparent phenotype of FIH ultimately express MEN1, we (59, 67) and others (2, 61) previously speculated that most kindreds with FIH were occult expressions of MEN1. The gene responsible for MEN1 has been cloned (15), leading to powerful gene sequencing methods applicable to MEN1, FIH, and other conditions (63). MEN2A, unlike MEN1, is not typically a consideration in the differential diagnosis of FIH, because the higher penetrance of medullary thyroid carcinoma and pheochromocytoma than of HPT in MEN2A dominates the clinical presentation in a family (42, 79, 86). FHH is an autosomal dominant trait usually causing mild HPT (62) with relative hypocalciuria; hypercalcemia in FHH is highly penetrant at all ages, even in the perinatal period (64). Mild hypermagnesemia is sometimes seen in FHH but is unusual in other forms of primary HPT (53, 64). FHH cases almost always remain hypercalcemic following standard subtotal parathyroidectomy (PTX) (64). FHH always presents 0025-7974/02/8101-0001/0 MEDICINE® 81: 1-26, 2002 Vol. 81, No. 1 Copyright

Rare Germline Mutations in Cyclin-Dependent Kinase Inhibitor Genes in Multiple Endocrine Neoplasia Type 1 and Related States

CONTEXT Germline mutation in the MEN1 gene is the usual cause of multiple endocrine neoplasia type 1 (MEN1). However, the prevalence of identifiable germline MEN1 mutations in familial MEN1 cases is only 70%. Some cases may have a germline mutation in another gene such as the p27 cyclin-dependent kinase inhibitor (CDKI). OBJECTIVE The aim of the study was to investigate cases of MEN1 or related states for germline mutations in all CDKI genes. METHODS A total of 196 consecutive index cases were selected with clear or suspected MEN1 and no identifiable germline MEN1 mutation. Every case was analyzed for germline mutation in each of the seven CDKI genes. RESULTS We identified benign polymorphisms of the CDKI genes and also 15 other initially unclassified sequence variants. After detailed gene/protein analysis, seven of these 15 variants were classified as probably pathological mutations. Three of these seven were probable mutations of p27. The remaining four were probable pathological mutations in three of the other CDKI genes, thereby implicating these three genes in the germline of human tumors. The identification rates for probably pathological mutations among the 196 index cases were similarly low for each of four CDKI genes: p15 (1%), p18 (0.5%), p21 (0.5%), and p27 (1.5%). No characteristic clinical subtype related to MEN1 was identified among the seven index cases and their families. CONCLUSION Rare germline mutation in any among four (p15, p18, p21, and p27) of the seven CDKIs is a probable cause of MEN1 or of some related states.

Genome-wide analysis of menin binding provides insights into MEN1 tumorigenesis.

Multiple endocrine neoplasia type I (MEN1) is a familial cancer syndrome characterized primarily by tumors of multiple endocrine glands. The gene for MEN1 encodes a ubiquitously expressed tumor suppressor protein called menin. Menin was recently shown to interact with several components of a trithorax family histone methyltransferase complex including ASH2, Rbbp5, WDR5, and the leukemia proto-oncoprotein MLL. To elucidate menins role as a tumor suppressor and gain insights into the endocrine-specific tumor phenotype in MEN1, we mapped the genomic binding sites of menin, MLL1, and Rbbp5, to approximately 20,000 promoters in HeLa S3, HepG2, and pancreatic islet cells using the strategy of chromatin-immunoprecipitation coupled with microarray analysis. We found that menin, MLL1, and Rbbp5 localize to the promoters of thousands of human genes but do not always bind together. These data suggest that menin functions as a general regulator of transcription. We also found that factor occupancy generally correlates with high gene expression but that the loss of menin does not result in significant changes in most transcript levels. One exception is the developmentally programmed transcription factor, HLXB9, which is overexpressed in islets in the absence of menin. Our findings expand the realm of menin-targeted genes several hundred-fold beyond that previously described and provide potential insights to the endocrine tumor bias observed in MEN1 patients.

Multiple endocrine neoplasia type 1: new clinical and basic findings

Multiple endocrine neoplasia type 1 (MEN1) provides a prime example of how a rare disease can advance our understanding of basic cell biology, neoplasia and common endocrine tumors. MEN1 is expressed mainly as parathyroid, enteropancreatic neuroendocrine, anterior pituitary and foregut carcinoid tumors. It is an autosomal dominant disease caused by mutation of the MEN1 gene. Since its identification, the MEN1 gene has been implicated in many common endocrine and non-endocrine tumors. This is a brief overview of recent scientific advances relating to MEN1, including newly recognized clinical features that are now better characterized by genetic analysis, insights into the function of the MEN1-encoded protein menin, and refined recommendations for mutation testing and tumor screening, which highlight our increasing understanding of this complex syndrome.

Molecular Pathology of the MEN1 Gene

Abstract: 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, NM23β, nonmuscle myosin heavy chain II‐A, GFAP, and/or vimentin. These partners have not clarified menins 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.

Parafibromin, product of the hyperparathyroidism-jaw tumor syndrome gene HRPT2, regulates cyclin D1/PRAD1 expression

Parafibromin is the 531-amino-acid protein product encoded by HRPT2, a putative tumor suppressor gene recently implicated in the autosomal dominant hyperparathyroidism–jaw tumor familial cancer syndrome, sporadic parathyroid cancer, and a minority of families with isolated hyperparathyroidism. Parafibromin contains no identified functional domains but bears sequence homology to Cdc73p, a budding yeast protein component of the RNA polymerase II-associated Paf1 complex. This study addressed the expression and functional properties of human parafibromin. A survey of human and mouse tissues analysed with polyclonal antibodies to parafibromin showed specific immunoreactivity in adrenal and parathyroid glands, kidney, heart, and skeletal muscle. Subcellular fractionation and laser confocal microscopy of normal human parathyroid gland demonstrated expression of parafibromin in both the cytoplasmic and nuclear compartments. Parafibromin was expressed in four parathyroid adenomas but was absent from two parathyroid carcinomas. Transient overexpression of wild-type parafibromin, but not its Leu64Pro missense mutant implicated in parathyroid cancer and familial isolated hyperparathyroidism, inhibited cell proliferation, and blocked expression of cyclin D1, a key cell cycle regulator previously implicated in parathyroid neoplasia. These results demonstrate that human parafibromin is a nucleocytoplasmic protein with functions consistent with its postulated role as a tumor suppressor protein.

The 32-Kilodalton Subunit of Replication Protein A Interacts with Menin, the Product of the MEN1 Tumor Suppressor Gene

ABSTRACT Menin is a 70-kDa protein encoded by MEN1, the tumor suppressor gene disrupted in multiple endocrine neoplasia type 1. In a yeast two-hybrid system based on reconstitution of Ras signaling, menin was found to interact with the 32-kDa subunit (RPA2) of replication protein A (RPA), a heterotrimeric protein required for DNA replication, recombination, and repair. The menin-RPA2 interaction was confirmed in a conventional yeast two-hybrid system and by direct interaction between purified proteins. Menin-RPA2 binding was inhibited by a number of menin missense mutations found in individuals with multiple endocrine neoplasia type 1, and the interacting regions were mapped to the N-terminal portion of menin and amino acids 43 to 171 of RPA2. This region of RPA2 contains a weak single-stranded DNA-binding domain, but menin had no detectable effect on RPA-DNA binding in vitro. Menin bound preferentially in vitro to free RPA2 rather than the RPA heterotrimer or a subcomplex consisting of RPA2 bound to the 14-kDa subunit (RPA3). However, the 70-kDa subunit (RPA1) was coprecipitated from HeLa cell extracts along with RPA2 by menin-specific antibodies, suggesting that menin binds to the RPA heterotrimer or a novel RPA1-RPA2-containing complex in vivo. This finding was consistent with the extensive overlap in the nuclear localization patterns of endogenous menin, RPA2, and RPA1 observed by immunofluorescence.