title: Characterization of p21Cip1/Waf1 peptide domains required for cyclin E/Cdk2 and PCNA interaction.
abstract: The cyclin-dependent kinase inhibitor p21Cip1/Waf1 is responsible for the p53-dependent growth arrest of cells in G1 phase following DNA damage. In the present study we investigated regions of p21 involved in inhibition of the G1/S phase cyclin-dependent kinase, cyclin E/Cdk2, as well as regions of p21 important for binding to this kinase and recombinant PCNA. To perform these studies we synthesized a series of overlapping peptides spanning the entire p21 sequence and used them in in vitro assays with cyclin E/Cdk2-immune complexes and with recombinant p21 and PCNA proteins. One amino-terminal p21 peptide spanning amino acids 15-40, antagonized p21 binding and inhibition of cyclin E/Cdk2 kinase. Antagonism of p21 binding was, however, lost in a similar peptide lacking amino acids 15-20, or in a peptide in which cysteine-18 was substituted for a serine. These results suggest that this peptide region is important for p21 interaction with cyclin E/Cdk2. A second peptide (amino acids 58-77) also antagonized p21-activity, but this peptide did not affect the ability of p21 to interact with cyclin E/Cdk2. A region of p21 larger than 26 amino acids is presumably required for Cdk-inhibition because none of the peptides we tested inhibited cyclin E/Cdk2. We also found that a peptide spanning amino acids 21-45 bound recombinant p21 in ELISA assays, and additional studies revealed a requirement for amino acids 26 through 45 for this interaction. A p21 peptide spanning amino acids 139-164 was found to bind PCNA in a filter binding assay and this peptide suppressed recombinant p21-PCNA interaction. Conformational analysis revealed that peptides spanning amino acids 21-45 and 139-164 tended towards an alpha-helical conformation in trifluoroethanol buffer, indicating that these regions are probably in a coiled conformation in the native protein. Taken together, our results provide an insight into domains of p21 that are involved in cyclin E/Cdk2 and PCNA interaction. Our results also suggest that a potential p21 dimerization domain may lie in the amino-terminus of p21. Continued exploration of these domains could prove useful in assessing p21-mimetic strategies for cancer treatment.
authors.affiliation: Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: I T
authors.initials: IT
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Akamatsu
authors.forename: M L
authors.initials: ML
authors.lastname: Smith
authors.forename: F D
authors.initials: FD
authors.lastname: Lung
authors.forename: D
authors.initials: D
authors.lastname: Duba
authors.forename: P P
authors.initials: PP
authors.lastname: Roller
authors.forename: A J
authors.initials: AJ
authors.lastname: Fornace
authors.forename: P M
authors.initials: PM
authors.lastname: O'Connor
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D042846:CDC2-CDC28 Kinases; D002460:Cell Line; D002942:Circular Dichroism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000737:chemistry* / Q000378:metabolism*; D016158:Genes, p53; D006801:Humans; D007951:Leukemia, Myeloid; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016339:Spectrometry, Mass, Fast Atom Bombardment; D014407:Tumor Cells, Cultured
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D010446:Peptide Fragments; D018809:Proliferating Cell Nuclear Antigen; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases