title: Somatic MED12 Nonsense Mutation Escapes mRNA Decay and Reveals a Motif Required for Nuclear Entry.
abstract: MED12 is a key component of the transcription-regulating Mediator complex. Specific missense and in-frame insertion/deletion mutations in exons 1 and 2 have been identified in uterine leiomyomas, breast tumors, and chronic lymphocytic leukemia. Here, we characterize the first MED12 5' end nonsense mutation (c.97G>T, p.E33X) identified in acute lymphoblastic leukemia and show that it escapes nonsense-mediated mRNA decay (NMD) by using an alternative translation initiation site. The resulting N-terminally truncated protein is unable to enter the nucleus due to the lack of identified nuclear localization signal (NLS). The absence of NLS prevents the mutant MED12 protein to be recognized by importin-α and subsequent loading into the nuclear pore complex. Due to this mislocalization, all interactions between the MED12 mutant and other Mediator components are lost. Our findings provide new mechanistic insights into the MED12 functions and indicate that somatic nonsense mutations in early exons may avoid NMD.
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Medicum, Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Tuomas
authors.initials: T
authors.lastname: Heikkinen
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Medicum, Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Kati
authors.initials: K
authors.lastname: Kämpjärvi
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Salla
authors.initials: S
authors.lastname: Keskitalo
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Department of Pathology, University of Helsinki, Helsinki, Finland.
authors.forename: Pernilla
authors.initials: P
authors.lastname: von Nandelstadh
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Institute of Biomedicine, University of Helsinki, Helsinki, Finland.
authors.forename: Ville
authors.initials: V
authors.lastname: Rantanen
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Medicum, Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Esa
authors.initials: E
authors.lastname: Pitkänen
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Matias
authors.initials: M
authors.lastname: Kinnunen
authors.affiliation: Hematology Research Unit Helsinki, Department of Hematology, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Helsinki, Finland.|Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Kuusanmäki
authors.affiliation: Hematology Research Unit Helsinki, Department of Hematology, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Helsinki, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Kontro
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Department of Pathology, University of Helsinki, Helsinki, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Turunen
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Medicum, Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Netta
authors.initials: N
authors.lastname: Mäkinen
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Department of Pathology, University of Helsinki, Helsinki, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Taipale
authors.affiliation: Institute for Molecular Medicine Finland (FIMM), University of Helsinki, Helsinki, Finland.
authors.forename: Caroline
authors.initials: C
authors.lastname: Heckman
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Finnish Cancer Institute, Helsinki, Finland.|Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Kaisa
authors.initials: K
authors.lastname: Lehti
authors.affiliation: Hematology Research Unit Helsinki, Department of Hematology, University of Helsinki and Helsinki University Hospital Comprehensive Cancer Center, Helsinki, Finland.|Department of Clinical Chemistry, University of Helsinki, Helsinki, Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Mustjoki
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Varjosalo
authors.affiliation: Research Programs Unit, Genome-Scale Biology, University of Helsinki, Helsinki, Finland.|Medicum, Department of Medical and Clinical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Pia
authors.initials: P
authors.lastname: Vahteristo
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D006801:Humans; D056892:Mediator Complex / Q000235:genetics*; D059365:Nonsense Mediated mRNA Decay; D059372:Nucleotide Motifs; D014176:Protein Biosynthesis; D034443:RNA Transport
chemical_list: D018389:Codon, Nonsense; C460107:MED12 protein, human; D056892:Mediator Complex
keywords: BioID; MED12; acute lymphoblastic leukemia (ALL); affinity purification mass spectrometry; nonsense mutation