title: Control of mTORC1 signaling by the Opitz syndrome protein MID1.
abstract: Mutations in the MID1 gene are causally linked to X-linked Opitz BBB/G syndrome (OS), a congenital disorder that primarily affects the formation of diverse ventral midline structures. The MID1 protein has been shown to function as an E3 ligase targeting the catalytic subunit of protein phosphatase 2A (PP2A-C) for ubiquitin-mediated degradation. However, the molecular pathways downstream of the MID1/PP2A axis that are dysregulated in OS and that translate dysfunctional MID1 and elevated levels of PP2A-C into the OS phenotype are poorly understood. Here, we show that perturbations in MID1/PP2A affect mTORC1 signaling. Increased PP2A levels, resulting from proteasome inhibition or depletion of MID1, lead to disruption of the mTOR/Raptor complex and down-regulated mTORC1 signaling. Congruously, cells derived from OS patients that carry MID1 mutations exhibit decreased mTORC1 formation, S6K1 phosphorylation, cell size, and cap-dependent translation, all of which is rescued by expression of wild-type MID1 or an activated mTOR allele. Our findings define mTORC1 signaling as a downstream pathway regulated by the MID1/PP2A axis, suggesting that mTORC1 plays a key role in OS pathogenesis.
authors.affiliation: Signal Transduction Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
authors.forename: Enbo
authors.initials: E
authors.lastname: Liu
authors.forename: Christine A
authors.initials: CA
authors.lastname: Knutzen
authors.forename: Sybille
authors.initials: S
authors.lastname: Krauss
authors.forename: Susann
authors.initials: S
authors.lastname: Schweiger
authors.forename: Gary G
authors.initials: GG
authors.lastname: Chiang
mesh_terms: D048429:Cell Size; D002478:Cells, Cultured; D004947:Esophagus / Q000002:abnormalities / Q000473:pathology; D006801:Humans; D006972:Hypertelorism / Q000209:etiology* / Q000473:pathology; D007021:Hypospadias / Q000209:etiology* / Q000473:pathology; D000076222:Mechanistic Target of Rapamycin Complex 1; D008868:Microtubule Proteins / Q000502:physiology*; D046912:Multiprotein Complexes; D009687:Nuclear Proteins / Q000502:physiology*; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases
chemical_list: D008868:Microtubule Proteins; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D011506:Proteins; D014157:Transcription Factors; C109052:MID1 protein, human; D044767:Ubiquitin-Protein Ligases; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D054648:Protein Phosphatase 2