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Functional analysis of the p57KIP2 gene mutation in Beckwith-Wiedemann syndrome
Z A Bhuiyan1, H Yatsuki, T Sasaguri
1Department of Bioscience, National Cardiovascular Center Research Institute, Suita, Osaka, Japan.
Abstract:
p57KIP2 is a potent tight-binding inhibitor of several G1 cyclin/cyclin-dependent kinase (Cdk) complexes, and is a negative regulator of cell proliferation. The gene encoding p57KIP2 is located at 11p15.5, a region implicated in both sporadic cancers and Beckwith-Wiedemann syndrome (BWS). Previously we demonstrated that p57KIP2 is imprinted and only the maternal allele is expressed in both mice and humans. We also showed mutations found in p57KIP2 in patients with BWS that were transmitted from the patients' carrier mothers, indicating that the expressed maternal allele was mutant and that the repressed paternal allele was normal. In the study reported here, we performed functional analysis of the two mutated p57KIP2 genes. We showed that the nonsense mutation found in the Cdk inhibitory domain in a BWS patient rendered the protein inactive with consequent complete loss of its role as a cell cycle inhibitor and of its nuclear localization. We also showed that the mutation in the QT domain, although completely retaining its cell cycle regulatory activity, lacked nuclear localization and was thus prevented from performing its role as an active cell cycle inhibitor. Consequently, no active p57KIP2 would have existed, which might have caused the disorders in BWS patients.
Insights
Mutations in the p57KIP2 gene disrupt its cell cycle inhibition function and nuclear localization, potentially causing Beckwith-Wiedemann syndrome (BWS). This research clarifies the molecular basis of BWS linked to p57KIP2 gene defects.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- p57KIP2 is a key negative regulator of cell proliferation, inhibiting G1 cyclin/cyclin-dependent kinase (Cdk) complexes.
- The p57KIP2 gene is located at 11p15.5, a locus associated with sporadic cancers and Beckwith-Wiedemann syndrome (BWS).
- p57KIP2 is imprinted, with only the maternal allele expressed in humans and mice.
Purpose of the Study:
- To functionally analyze two mutated p57KIP2 genes identified in Beckwith-Wiedemann syndrome (BWS) patients.
- To investigate the impact of specific mutations on p57KIP2 protein activity, cell cycle inhibition, and subcellular localization.
Main Methods:
- Functional analysis of mutated p57KIP2 genes.
- Assessment of protein activity, cell cycle inhibition capacity, and nuclear localization.
Main Results:
- A nonsense mutation in the Cdk inhibitory domain abolished p57KIP2 protein activity and nuclear localization, eliminating its cell cycle inhibitory role.
- A mutation in the QT domain retained cell cycle regulatory activity but prevented nuclear localization, thus inhibiting its function as a cell cycle inhibitor.
- Both mutations resulted in a lack of active p57KIP2, suggesting a potential cause for BWS.
Conclusions:
- Mutations in p57KIP2, particularly those affecting nuclear localization and inhibitory function, are implicated in the pathogenesis of Beckwith-Wiedemann syndrome (BWS).
- The functional inactivation of p57KIP2 due to these mutations disrupts normal cell cycle regulation, leading to developmental abnormalities characteristic of BWS.