title: Menin missense mutants encoded by the MEN1 gene that are targeted to the proteasome: restoration of expression and activity by CHIP siRNA.
abstract: BACKGROUND
  In multiple endocrine neoplasia type 1 (MEN1) characterized by tumors of parathyroid, enteropancreas, and anterior pituitary, missense mutations in the MEN1 gene product, menin, occur in a subset of cases. The mutant proteins are degraded by the proteasome. However, whether their expression and activity can be restored is not known.
  
  
  OBJECTIVE
  Our objective was to functionally characterize a panel of 16 menin missense mutants, including W423R and S443Y identified in new MEN1 families, with respect to protein stability, targeting to the proteasome and restoration of expression by proteasome inhibitors and expression and function by small interfering RNA technology.
  
  
  METHODS
  Flag-tagged wild-type (WT) and missense menin mutant expression vectors were transiently transfected in human embryonic kidney (HEK293) and/or rat insulinoma (Rin-5F) cells.
  
  
  RESULTS
  The majority of mutants were short-lived, whereas WT menin was stable. Proteasome inhibitors MG132 and PS-341 and inhibition of the chaperone, heat-shock protein 70 (Hsp70), or the ubiquitin ligase, COOH terminus of Hsp70-interacting protein (CHIP), by specific small interfering RNA, restored the levels of the mutants, whereas that of WT menin was largely unaffected. Inhibition of CHIP restored the ability of mutants to mediate normal functions of menin: TGF-β up-regulation of the promoters of its target genes, the cyclin-dependent kinase inhibitors p15 and p21 as well as TGF-β inhibition of cell numbers.
  
  
  CONCLUSIONS
  When the levels of missense menin mutants that are targeted to the proteasome are normalized they may function similarly to WT menin. Potentially, targeting specific components of the proteasome chaperone pathway could be beneficial in treating a subset of MEN1 cases.
authors.affiliation: Department of Medicine, Calcium Research Laboratory, and Hormones and Cancer Research Unit, Royal Victoria Hospital, McGill University, Montreal, Quebec H3A 1A1, Canada.
authors.forename: Lucie
authors.initials: L
authors.lastname: Canaff
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Vanbellinghen
authors.forename: Ippei
authors.initials: I
authors.lastname: Kanazawa
authors.forename: Hayeon
authors.initials: H
authors.lastname: Kwak
authors.forename: Natasha
authors.initials: N
authors.lastname: Garfield
authors.forename: Line
authors.initials: L
authors.lastname: Vautour
authors.forename: Geoffrey N
authors.initials: GN
authors.lastname: Hendy
mesh_terms: D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D005190:Family; D005786:Gene Expression Regulation / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D059748:Proteolysis / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology*; D051381:Rats; D014407:Tumor Cells, Cultured; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors* / Q000235:genetics
chemical_list: C105373:MEN1 protein, human; D050505:Mutant Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; C467728:STUB1 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex