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MED12 mutations link intellectual disability syndromes with dysregulated GLI3-dependent Sonic Hedgehog signaling.

ABSTRACT: Recurrent missense mutations in the RNA polymerase II Mediator subunit MED12 are associated with X-linked intellectual disability (XLID) and multiple congenital anomalies, including craniofacial, musculoskeletal, and behavioral defects in humans with FG (or Opitz-Kaveggia) and Lujan syndromes. However, the molecular mechanism(s) underlying these phenotypes is poorly understood. Here we report that MED12 mutations R961W and N1007S causing FG and Lujan syndromes, respectively, disrupt a Mediator-imposed constraint on GLI3-dependent Sonic Hedgehog (SHH) signaling. We show that the FG/R961W and Lujan/N1007S mutations disrupt the gene-specific association of MED12 with a second Mediator subunit, CDK8, identified herein to be a suppressor of GLI3 transactivation activity. In FG/R961W and Lujan/N1007S patient-derived cells, we document enhanced SHH pathway activation and GLI3-target gene induction coincident with impaired recruitment of CDK8 onto promoters of GLI3-target genes, but not non-GLI3-target genes. Together, these findings suggest that dysregulated GLI3-dependent SHH signaling contributes to phenotypes of individuals with FG and Lujan syndromes and further reveal a basis for the gene-specific manifestation of pathogenic mutations in a global transcriptional coregulator.

SUBMITTER: Zhou H

PROVIDER: S-EPMC3511715 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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MED12 mutations link intellectual disability syndromes with dysregulated GLI3-dependent Sonic Hedgehog signaling.

Zhou Haiying H Spaeth Jason M JM Kim Nam Hee NH Xu Xuan X Friez Michael J MJ Schwartz Charles E CE Boyer Thomas G TG

Proceedings of the National Academy of Sciences of the United States of America 20121022 48

Recurrent missense mutations in the RNA polymerase II Mediator subunit MED12 are associated with X-linked intellectual disability (XLID) and multiple congenital anomalies, including craniofacial, musculoskeletal, and behavioral defects in humans with FG (or Opitz-Kaveggia) and Lujan syndromes. However, the molecular mechanism(s) underlying these phenotypes is poorly understood. Here we report that MED12 mutations R961W and N1007S causing FG and Lujan syndromes, respectively, disrupt a Mediator-i ...[more]

PMID: 23091001

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Project description:BACKGROUND:Mutations in mediator of RNA polymerase II transcription subunit 12 homolog (MED12, OMIM 300188) cause X-linked intellectual disability (XLID) disorders including FG, Lujan, and Ohdo syndromes. The Gli3-dependent Sonic Hedgehog (SHH) signaling pathway has been implicated in the original FG syndrome and Lujan syndrome. How are SHH-signaling defects related to the complex clinical phenotype of MED12-associated XLID syndromes are not fully understood. METHODS:Quantitative RT-PCR was used to study expression levels of three SHH-signaling genes in lymophoblast cell lines carrying four MED12 mutations from four unrelated XLID families. Genotype and phenotype correlation studies were performed on these mutations. RESULTS:Three newly identified and one novel MED12 mutations in six affected males from four unrelated XLID families were studied. Three mutations (c.2692A>G; p.N898D, c.3640C>T; p.R1214C, and c.3884G>A; p.R1295H) are located in the LS domain and one (c.617G>A; p.R206Q) is in the L domain of MED12. These mutations involve highly conserved amino acid residues and segregate with ID and related congenital malformations in respective probands families. Patients with the LS-domain mutations share many features of FG syndrome and some features of Lujan syndrome. The patient with the L-domain mutation presented with ID and predominant neuropsychiatric features but little dysmorphic features of either FG or Lujan syndrome. Transcript levels of three Gli3-dependent SHH-signaling genes, CREB5, BMP4, and NEUROG2, were determined by quantitative RT-PCR and found to be significantly elevated in lymphoblasts from patients with three mutations in the MED12-LS domain. CONCLUSIONS:These results support a critical role of MED12 in regulating Gli3-dependent SHH signaling and in developing ID and related congenital malformations in XLID syndromes. Differences in the expression profile of SHH-signaling genes potentially contribute to variability in clinical phenotypes in patients with MED12-related XLID disorders.

Project description:Cancer genomics has revealed many genes and core molecular processes that contribute to human malignancies, but the genetic and molecular bases of many rare cancers remains unclear. Genetic predisposition accounts for 5 to 10% of cancer diagnoses in children1,2, and genetic events that cooperate with known somatic driver events are poorly understood. Pathogenic germline variants in established cancer predisposition genes have been recently identified in 5% of patients with the malignant brain tumour medulloblastoma3. Here, by analysing all protein-coding genes, we identify and replicate rare germline loss-of-function variants across ELP1 in 14% of paediatric patients with the medulloblastoma subgroup Sonic Hedgehog (MBSHH). ELP1 was the most common medulloblastoma predisposition gene and increased the prevalence of genetic predisposition to 40% among paediatric patients with MBSHH. Parent-offspring and pedigree analyses identified two families with a history of paediatric medulloblastoma. ELP1-associated medulloblastomas were restricted to the molecular SHH? subtype4 and characterized by universal biallelic inactivation of ELP1 owing to somatic loss of chromosome arm 9q. Most ELP1-associated medulloblastomas also exhibited somatic alterations in PTCH1, which suggests that germline ELP1 loss-of-function variants predispose individuals to tumour development in combination with constitutive activation of SHH signalling. ELP1 is the largest subunit of the evolutionarily conserved Elongator complex, which catalyses translational elongation through tRNA modifications at the wobble (U34) position5,6. Tumours from patients with ELP1-associated MBSHH were characterized by a destabilized Elongator complex, loss of Elongator-dependent tRNA modifications, codon-dependent translational reprogramming, and induction of the unfolded protein response, consistent with loss of protein homeostasis due to Elongator deficiency in model systems7-9. Thus, genetic predisposition to proteome instability may be a determinant in the pathogenesis of paediatric brain cancers. These results support investigation of the role of protein homeostasis in other cancer types and potential for therapeutic interference.

Dataset Information

MED12 mutations link intellectual disability syndromes with dysregulated GLI3-dependent Sonic Hedgehog signaling.

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MED12 mutations link intellectual disability syndromes with dysregulated GLI3-dependent Sonic Hedgehog signaling.

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