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Experimental Approaches to Study Mitochondrial Localization and Function of a Nuclear Cell Cycle Kinase, Cdk1
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Increased protein stability of CDKN1C causes a gain-of-function phenotype in patients with IMAGe syndrome

Naoki Hamajima1, Yoshikazu Johmura, Satoshi Suzuki

  • 1Department of Pediatrics, Nagoya City West Medical Center, Nagoya, Aichi, Japan.

Plos One
|October 8, 2013
PubMed

Insights

IMAGe syndrome mutations in the CDKN1C gene increase protein stability, explaining the characteristic reduced-growth phenotype. This gain-of-function mechanism, not previously understood, offers new insights into the disorder.

Area of Science:

  • Genetics
  • Molecular Biology
  • Developmental Biology

Background:

  • Mutations in the CDKN1C gene's PCNA-binding domain are linked to IMAGe syndrome.
  • Previous understanding suggested PCNA binding loss and altered monoubiquitination explained the phenotype.
  • This hypothesis did not fully account for the observed growth reduction.

Purpose of the Study:

  • To investigate the molecular mechanism underlying IMAGe syndrome.
  • To determine how CDKN1C mutations lead to the characteristic reduced-growth phenotype.
  • To explore the role of protein stability in IMAGe syndrome pathogenesis.

Main Methods:

  • Identification of a novel CDKN1C mutation (c.815T>G, p.Ile272Ser) in affected siblings and an unaffected carrier.
  • Assessment of PCNA binding disruption in IMAGe-associated CDKN1C mutants.
  • Protein stability assays using cycloheximide and proteasome inhibitor MG132.

Main Results:

  • IMAGe-associated CDKN1C mutations significantly increase protein stability.
  • PCNA binding is disrupted by mutations like p.Ile272Ser, p.Asp274Asn, and p.Phe276Val.
  • Mutant CDKN1C proteins resist degradation, unlike wild-type, indicating enhanced stability.

Conclusions:

  • The reduced-growth phenotype in IMAGe syndrome is likely caused by CDKN1C gain-of-function.
  • Increased protein stability of CDKN1C is the key mechanism driving IMAGe syndrome.
  • This finding reframes the understanding of IMAGe syndrome pathogenesis from loss-of-function to gain-of-function.

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