title: Inhibition of CDK activity and PCNA-dependent DNA replication by p21 is blocked by interaction with the HPV-16 E7 oncoprotein.
abstract: p21 inhibits cyclin-dependent kinase (CDK) activity and proliferating cell nuclear antigen (PCNA)-dependent DNA replication by binding to CDK/cyclin complexes and to PCNA through distinct domains. The human papillomavirus (HPV)-16 E7 oncoprotein (16E7) abrogated a DNA damage-induced cell cycle arrest in vivo, despite high levels of p21. Using cell lysates and purified proteins we show that 16E7 prevented p21 both from inhibiting CDK2/cyclin E activity and PCNA-dependent DNA replication, whereas the nononcogenic HPV-6 E7 had reduced effects. Inactivation of both inhibitory functions of p21 was attained through binding between 16E7 and sequences in the carboxy-terminal end of p21 that overlap with the PCNA-binding site and the second p21 cyclin-binding motif. These data imply that the carboxyl terminus of p21 simultaneously modulates both CDK activity and PCNA-dependent DNA replication and that a single protein, 16E7, can override this modulation to disrupt normal cell cycle control.
authors.affiliation: Program in Cancer Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
authors.forename: J O
authors.initials: JO
authors.lastname: Funk
authors.forename: S
authors.initials: S
authors.lastname: Waga
authors.forename: J B
authors.initials: JB
authors.lastname: Harry
authors.forename: E
authors.initials: E
authors.lastname: Espling
authors.forename: B
authors.initials: B
authors.lastname: Stillman
authors.forename: D A
authors.initials: DA
authors.lastname: Galloway
mesh_terms: D001665:Binding Sites; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects*; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism / Q000821:virology; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D018809:Proliferating Cell Nuclear Antigen; D011994:Recombinant Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases