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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Binding Sites
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CDC2-CDC28 Kinases*
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclin-Dependent Kinases / antagonists & inhibitors
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Cyclin-Dependent Kinases / genetics
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Cyclin-Dependent Kinases / metabolism*
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Cyclins / drug effects
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Cyclins / genetics
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Cyclins / metabolism*
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DNA Replication / drug effects*
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Humans
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Keratinocytes / metabolism
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Keratinocytes / virology
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Oncogene Proteins, Viral / genetics
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Oncogene Proteins, Viral / metabolism*
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Papillomavirus E7 Proteins
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Proliferating Cell Nuclear Antigen / metabolism
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Proliferating Cell Nuclear Antigen / pharmacology*
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / metabolism
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
Substances
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CDKN1A protein, human
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Oncogene Proteins, Viral
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Papillomavirus E7 Proteins
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Proliferating Cell Nuclear Antigen
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Recombinant Proteins
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oncogene protein E7, Human papillomavirus type 16
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Protein Serine-Threonine Kinases
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CDC2-CDC28 Kinases
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CDK2 protein, human
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinases