title: Menin missense mutants associated with multiple endocrine neoplasia type 1 are rapidly degraded via the ubiquitin-proteasome pathway.
abstract: MEN1 is a tumor suppressor gene that is responsible for multiple endocrine neoplasia type 1 (MEN1) and that encodes a 610-amino-acid protein, called menin. While the majority of germ line mutations identified in MEN1 patients are frameshift and nonsense mutations resulting in truncation of the menin protein, various missense mutations have been identified whose effects on menin activity are unclear. For this study, we analyzed a series of menin proteins with single amino acid alterations and found that all of the MEN1-causing missense mutations tested led to greatly diminished levels of the affected proteins in comparison with wild-type and benign polymorphic menin protein levels. We demonstrate here that the reduced levels of the mutant proteins are due to rapid degradation via the ubiquitin-proteasome pathway. Furthermore, the mutants, but not wild-type menin, interact both with the molecular chaperone Hsp70 and with the Hsp70-associated ubiquitin ligase CHIP, and the overexpression of CHIP promotes the ubiquitination of the menin mutants in vivo. These findings reveal that MEN1-causing missense mutations lead to a loss of function of menin due to enhanced proteolytic degradation, which may be a common mechanism for inactivating tumor suppressor gene products in familial cancer.
authors.affiliation: Tumor Endocrinology Project, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. nohkura@gan2.res.ncc.go.jp
authors.forename: Hiroko
authors.initials: H
authors.lastname: Yaguchi
authors.forename: Naganari
authors.initials: N
authors.lastname: Ohkura
authors.forename: Maho
authors.initials: M
authors.lastname: Takahashi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Nagamura
authors.forename: Issay
authors.initials: I
authors.lastname: Kitabayashi
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Tsukada
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D016147:Genes, Tumor Suppressor; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry; D051379:Mice; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000378:metabolism*; D018761:Multiple Endocrine Neoplasia Type 1 / Q000235:genetics*; D009154:Mutation; D020125:Mutation, Missense; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011110:Polymorphism, Genetic; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D012313:RNA / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002843:Chromatin; D018840:HSP70 Heat-Shock Proteins; C105373:MEN1 protein, human; D009097:Multienzyme Complexes; D010455:Peptides; D011518:Proto-Oncogene Proteins; D025801:Ubiquitin; D012313:RNA; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex