p57 & Beckwith-Wiedemann syndrome (BWS) By: Adam Drechsler

p57(kip2) is a CDK inhibitor Cyclin D CDK4 CDK4 Ink4 Inhibitors p16 Images from Bob Duronio’s powerpoint’s entitled “Cell Cycle 2”. When p57 binds to the cyclin/cdk it binds to a domain that prevents ATP binding and catalytic activity. -Adopts various 3d structures after binding to proteins. Late folding could explain why CKIS are capable of interacting with a variety of proteins to regulate various cell functions. Cyclin CDK p57 Cyclin CDK Cip/Kip Proteins p57

p57- location of action p57 is: -A tumor suppressor -Localized to chromosome 11p15 -Down regulated by IGF-2 -An inhibitor of G1 Cyclin-CDK complexes -At low levels a stimulator of cycD-CDK4/6 Images of p57 and cell cycle map from Todd G. Mainprize in “Cip/Kip cell-cycle inhibitors: A neuro-onological perspective”. Journal of Neuro-Oncology 51:205-218, 2001 At low levels p57, the assembly of cyclin-D/cdk4 complexes are increased. Mouse Embryo Fibroblast’s lacking p57 failed to assemble detectable quantities of cylcinD-cdk complexes. However, reintroduction of p57 restored cyclin D to physiological levels, proving that p57 is necessary to the cell cycle. P57 is localized to chromosome 11p15.5.

p57 Mouse Knockout Targeted disruption of mouse p57(kip2) gene. Targeting construct removes exons 1 and 2. -A construct that removes almost 90% of the p57 coding region was inserted into embryonic stem cells. -Gancyclovir-resistant cells were screened for homologous recombination by Southern blot analysis. -Homologous recombinants inserted into blastocoel cavity of early embryo C57BL/6 mice (specific cell-line). -Male chimeras were mated to C57BL/6 females. F1 heterozygotes were back-crossed to C57BL/6 to maintain the disrupted allele.

In the absence of p57… p57 -/- : Embryonic/neonatal lethality, multiple developmental defects, altered cell proliferation and differentiation. p57 +/- : Same as above, or Wild-type expression Mice lacking p57 have umbilical hernia, body wall muscle dysplasia, neonatal lethality, renal medullary dysplasia, adrenal cortex hyperplasia Western Blot Analysis

Genomic Imprinting Gene expressed in a parent-of-origin specific manner. Paternal imprint of p57 Image: http://atlasgeneticsoncology.org/Deep/GenomImprintID20032.html Paternal allele is transcriptionally repressed. Paternal allele is not fully imprinted. Expressed at very low levels in most tissues

To add to the complexity… Highly variable penetrance Displays subset of all phenotypes. 85% sporadic CDK Inhibitor Domain Proline Rich Domain Images of p57 and cell cycle map from Todd G. Mainprize in “Cip/Kip cell-cycle inhibitors: A neuro-onological perspective”. Journal of Neuro-Oncology 51:205-218, 2001 -The N-terminus of all cip/kip proteins contain a homologous domain responsible for CDK binding and inhibitory function. -Proline rich domain and acidic domain mediate protein-protein interactions. -The QT domain is only seen in p27 and p57 and contains the nuclear localizing sequences. When p57 binds to the cyclin/cdk it binds to a domain that prevents ATP binding and catalytic activity. -Adopts various 3d structures after binding to proteins. Late folding could explain why CKIS are capable of interacting with a variety of proteins to regulate various cell functions. Acidic Domain QT Domain

Complex pattern of inheritance 15% of cases are familial Autosomal dominant inheritance with variable expressivity (if mutated allele is inherited from mother) Uniparental disomy Trisomy of chromosome 11p15.5 Duplication of this chromosome Translocations involving maternal 11p.15.5 Familial cases of BWS are inherited in an autosomal dominant mode but exclusively through the mother (ex of mother with mutation in her maternal p57 allele but normal paternal allele crossed with normal father).

Beckwith-Wiedemann Syndrome Growth abnormalities Somatic Overgrowth Macroglossia Gigantism Enlarged adrenal glands Ear creases Visceromegaly (enlarged organs) Omphalocele (umbilical hernia) Kidney abnormalities Advanced aging Birth weight and height > 90 percentile 1000-fold increase in risk of devloping childhood tumors. Image: http://jmg.bmj.com/cgi/reprint/31/7/560 (J. Med. Genet. 1994;31;560-564 “Beckwith-Wiedemann Syndrome”. Author: M Elliott) An 8 month old boy with BWS. Macroglossia, maxillary hypoplasia, and facial hemihypertrophy are present. Macroglossia frequency in BWS is 99%

Additional BWS information Good prognosis Children usually grow up to become normal heights. Mortality Risk Infant Mortality < 20% Why do they grow up to be normal adults? Because p57 expression is normally only high during embryogenesis, there is a high expression of p57 in most tissues and this decreases to very low levels in the adult. BWS can be diagnosed during pregnancy. Prenatal ultrasound can detect fetal abdominal wall defects and macrosomia that suggest that the fetus has BWS.

Summary p57 is a cip/kip inhibitor p57 inhibits action by cyclin/cdk complexes and prevents transition from G1 to S The paternal p57 gene is imprinted. p57 is high during embryogenesis and its expression decreases toward adulthood 85% of cases are sporadic Loss of p57 function is the cause of Beckwith-Wiedemann syndrome IGF-2 may play a role in the development of BWS.