Tumor suppressor menin: the essential role of nuclear localization signal domains in coordinating gene expression.
Menin is encoded by the tumor suppressor gene MEN1 that is mutated in patients with an inherited tumor syndrome, multiple endocrine neoplasia type 1 (MEN1). Although menin is a nuclear protein and directly binds to DNA through its nuclear localization signals (NLSs), the precise role for each of the NLSs in nuclear translocation and gene expression remains to be elucidated. Here, we show that point mutations in three individual NLSs, NLS1, NLS2, and a novel accessory NLS, NLSa, do not block nuclear translocation, but compromise the ability of menin to repress expression of the endogenous insulin-like growth factor binding protein-2 (IGFBP-2) gene. This repression is not released by an inhibitor of histone deacetylases. Although subtle mutations in menin NLSs do not affect menin association with chromatin, they abolish menin binding to the IGFBP-2 promoter in vivo. Furthermore, each of the NLSs is also crucial for menin-mediated induction of caspase 8 expression. Together, these results suggest that menin may act as a scaffold protein in coordinating activation and repression of gene transcription and that its NLSs play a more important role in controlling gene transcription than merely targeting menin into the nucleus.
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Department of Cancer Biology, Abramson Family Cancer Research Institute, Abramson Cancer Center, University of Pennsylvania, Philadelphia, USA.
Desmond
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A
Hou
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Silva
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Schnepp
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RW
Hua
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D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019913:Nuclear Localization Signals / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D021381:Protein Transport / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D018971:Insulin-Like Growth Factor Binding Protein 2; C105373:MEN1 protein, human; D019913:Nuclear Localization Signals; D011518:Proto-Oncogene Proteins; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases