Increased protein stability of CDKN1C causes a gain-of-function phenotype in patients with IMAGe syndrome

PLoS One. 2013 Sep 30;8(9):e75137. doi: 10.1371/journal.pone.0075137. eCollection 2013.

Abstract

Mutations in the proliferating cell nuclear antigen (PCNA)-binding domain of the CDKN1C gene were recently identified in patients with IMAGe syndrome. However, loss of PCNA binding and suppression of CDKN1C monoubiquitination by IMAGe-associated mutations hardly explain the reduced-growth phenotype characteristic of IMAGe syndrome. We demonstrate here that IMAGe-associated mutations in the CDKN1C gene dramatically increased the protein stability. We identified a novel heterozygous mutation, c.815T>G (p.Ile272Ser), in the CDKN1C gene in three siblings manifesting clinical symptoms associated with IMAGe syndrome and their mother (unaffected carrier). PCNA binding to CDKN1C was disrupted in the case of p.Ile272Ser, and for two other IMAGe-associated mutations, p.Asp274Asn and p.Phe276Val. Intriguingly, the IMAGe-associated mutant CDKN1C proteins were fairly stable even in the presence of cycloheximide, whereas the wild-type protein was almost completely degraded via the proteasome pathway, as shown by the lack of degradation with addition of a proteasome inhibitor, MG132. These results thus suggested that the reduced-growth phenotype of IMAGe syndrome derives from CDKN1C gain-of-function due to IMAGe-associated mutations driving increased protein stability.

MeSH terms

  • Adrenal Insufficiency
  • Base Sequence
  • Blotting, Western
  • Cyclin-Dependent Kinase Inhibitor p57 / genetics*
  • Cyclin-Dependent Kinase Inhibitor p57 / metabolism*
  • Cycloheximide
  • Exome / genetics
  • Female
  • Fetal Growth Retardation
  • Flow Cytometry
  • Gene Components
  • Humans
  • Leupeptins
  • Male
  • Molecular Sequence Data
  • Mutation, Missense / genetics
  • Osteochondrodysplasias
  • Pedigree
  • Phenotype*
  • Proliferating Cell Nuclear Antigen / metabolism*
  • Protein Stability*
  • Sequence Analysis, DNA
  • Siblings
  • Urogenital Abnormalities

Substances

  • CDKN1C protein, human
  • Cyclin-Dependent Kinase Inhibitor p57
  • Leupeptins
  • Proliferating Cell Nuclear Antigen
  • Cycloheximide
  • benzyloxycarbonylleucyl-leucyl-leucine aldehyde

Supplementary concepts

  • Intrauterine Growth Retardation, Metaphyseal Dysplasia, Adrenal Hypoplasia Congenita, And Genital Anomalies

Grant support

The authors have no support or funding to report.