of work The protein p21 (Cip1, Waf1, Sdi1) is a potent inhibitor of cyclin dependent kinases (CDKs) and cyclins. P21 can also block DNA replication through its interaction with the proliferating cell nuclear antigen (PCNA) which is an auxiliary factor for polymerase delta;. In addition to its role on replication, PCNA is clearly implicated in the repair resynthesis step of nucleotide excision repair (NER). Since PCNA particpates in both DNA repair and replication, it has been speculated that p21 might also regulate NER through its interaction with PCNA. Previous studies on the role of p21 on NER have yielded contradictory results that make it difficult to reach a general consensus with regard to the precise role of p21 in NER. We have investigated the effect of p21 on NER both in vitro and in vivo using purified fragments of p21 containing either the CDK-binding domain or the PCNA-binding domain of the protein. The results show that the C-terminal domain of the p21 protein, which binds to PCNA, inhibits NER both in vitro and in vivo. A 50% percent inhibition of in vitro NER occurred at a ratio of 50:1 p21 C-terminus to PCNA monomer. This is a specific function of the C-terminal end of p21 since the N-terminal of the protein had no effect on nucleotide excision repair. Our results suggest that the inhibition occurs at the resynthesis step of the repair process. We further demonstrate that the inhibition of DNA repair is mediated via binding of p21 to PCNA since it is relieved by addition of purified PCNA protein. We conclude that the effect of p21 on DNA repair occurs at much higher concentrations than its effect on DNA replication. P21 might serve as an intracellular regulator of these two processesWe are currently exploring if P21 also participates in another major DNA repair pathway, that of Base excision repair (BER). PCNA is involved in the long patch BER repair and we expect that p21 will influence that pathway as well. Further, it is being examined whether p21 also affects the DNA repair in mitochondria, where base excision also operates.

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National Institute on Aging (NIA)
Intramural Research (Z01)
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Maynard, Scott; Swistowska, Anna Maria; Lee, Jae Wan et al. (2008) Human embryonic stem cells have enhanced repair of multiple forms of DNA damage. Stem Cells 26:2266-74
Hyun, Moonjung; Lee, Jihyun; Lee, Kyungjin et al. (2008) Longevity and resistance to stress correlate with DNA repair capacity in Caenorhabditis elegans. Nucleic Acids Res 36:1380-9
Lukas, Jiri; Bohr, Vilhelm A; Halazonetis, Thanos D (2006) Cellular responses to DNA damage: current state of the field and review of the 52nd Benzon Symposium. DNA Repair (Amst) 5:591-601
Deeg, H Joachim; Friedman, Debra; Bohr, Vilhelm A et al. (2006) Transplantation and aging. Biol Blood Marrow Transplant 12:893-8
Bohr, Vilhelm A; Sander, Miriam; Kraemer, Kenneth H (2005) Rare diseases provide rare insights into DNA repair pathways, TFIIH, aging and cancer center. DNA Repair (Amst) 4:293-302
Bohr, Vilhelm A; Metter, E Jeffery; Harrigan, Jeanine A et al. (2004) Werner syndrome protein 1367 variants and disposition towards coronary artery disease in Caucasian patients. Mech Ageing Dev 125:491-6
Bendixen, Mette H; Nexo, Bjorn A; Bohr, Vilhelm A et al. (2004) A polymorphic marker in the first intron of the Werner gene associates with cognitive function in aged Danish twins. Exp Gerontol 39:1101-7
Brosh Jr, Robert M; Bohr, Vilhelm A (2002) Roles of the Werner syndrome protein in pathways required for maintenance of genome stability. Exp Gerontol 37:491-506
Rosner, K; Winter, D B; Skovgaard, G L et al. (2001) Analysis of microsatellite instability and hypermutation of immunoglobulin variable genes in Werner syndrome. Mech Ageing Dev 122:1121-33
Soe, K; Dianov, G; Nasheuer, H P et al. (2001) A human topoisomerase I cleavage complex is recognized by an additional human topisomerase I molecule in vitro. Nucleic Acids Res 29:3195-203