p57(KIP2) and Beckwith-Wiedemann Syndrome Shannon O’Leary

General Information about p57 member of the p21/p27 family of CKIs (cyclin kinase inhibitor) potent tight-binding inhibitor of several G1 cyclin/Cdk complexes (cdk2, cdk4, cyclins E, A, and D) negative regulator of cell proliferation localizes to the nucleus primarily expressed in terminally differentiated cells possible tumor suppressor

History found in 1995 by a process called the two- hybrid system used to isolate proteins that physically associate with other target proteins p57 was discovered as a cyclin D binding protein

Normal Function the cyclinE/cdk2 complex hyperphosphorylates Rb when Rb is hyperphosphorylated it no longer inhibits E2F E2F controls the expression of genes required fro DNA synthesis, including those of the pre-replication complex

Inhibits proliferation p57 binds to the cyclinE/cdk2 complex, inhibiting its activity when it does this, Rb cannot be hyperphosphorylated and E2F remains inhibited CyclinE/cdk2 also has other roles in the G1-S transition RESULT: the DNA cannot replicate and the cell remains in G1

Problem: when p57 is mutated or missing, cells cannot stop proliferating and if this occurs in embryonic cells, then the cells will not differentiate

Mouse Knockout Experiment Biology 169; Spring 2004 Lecture Notes

dxgmon2.html first the amount of p57 was measured during embryonic development high levels were found throughout the organism this suggests that p57 may be up-regulated when cells exit the cell cycle and start to differentiate

Results mutant alleles were introduced by homologous recombination into embryonic stem cells more than 90% of the newborn mice died within several hours after birth with various anatomical defects -short limbs -difficulty suckling (probably result of a cleft palate) -inflated GI tract -shortened and abnormal intestine -shortened and abnormal intestine -base of the skull underdeveloped -base of the skull underdeveloped

Humans and p57 p57 is located at 11p15.5, making it a potential tumor suppressor this region has been investigated intensively because of frequent loss of heterozygosity at this locus in a number of human cancers this region has been investigated intensively because of frequent loss of heterozygosity at this locus in a number of human cancers several types of childhood tumors also display loss of 11p15 alleles can.snu.ac.kr/Database/ChromosomalLoc ations.asp

Beckwith-Wiedemann Syndrome (BWS) after the mouse-knockout experiment researchers tied p57 to Beckwith- Wiedemann Syndrome because areas affected in the mice by the p57 mutant were similar to the areas affected in BWS patients

BWS is characterized by numerous growth abnormalities, including macroglossia (enlarged tongue), gigantism, visceromegely (enlarged organs), exomphalos (umbilical protrusion), microcephaly (small head) and an increased risk of childhood tumors 76.htm

Biology 169; Spring 2004 Lecture Notes BWS occurs in 1 in 13,700 births, 85% sporadic and 15% familial (research indicates maternal carriers)

in 1996, 9 cases of patients with BWS were studied and mutations in the p57 gene occurred twice in 1997, another 40 BWS patients were analyzed and only 2 (5%) showed mutations in the p57 gene the low frequency of p57 mutations, suggests that BWS can involve disruption of multiple independent genes on 11p15.5, not just the p57 gene studies have been done indicating that many other gene mutations at location 11p15.5 contribute to BWS

Conclusion Although p57 may not be the only gene responsible for BWS, it does play a highly important function in the regulation of the cell cycle and its loss of function certainly plays a role in development and may also play a role in many cancers. Much research is yet to be done.