Abstract
The effect of overexpression of p21waf1 on drug sensitivity was studied in an osteosarcoma cell line (SaOs-2) lacking both p53 and functional retinoblastoma protein using a tetracycline (TC)-inducible expression system. p21waf1 expression was barely detectable in SaOS-2 cells incubated in the presence of TC. After TC withdrawal, high levels of p21waf1 were induced in these cells. These p21waf1-induced cells showed increased sensitivity to doxorubicin, tomudex, and methotrexate as compared to uninduced cells; this condition is associated with increased apoptosis. Expression of p21waf1 reduced cyclin A-associated kinase activity and, surprisingly, resulted in inhibition of phosphorylation of E2F-1 and increased E2F-1 binding activity. An S-G2 cell cycle arrest/delay and an increase in expression of E2F-responsive genes (dihydrofolate reductase and thymidylate synthase) was correspondingly observed. Overexpression of p21waf1 in cells lacking functional retinoblastoma protein may mediate sensitivity to anticancer drugs by inhibiting E2F-1 phosphorylation, which may contribute to increased S-G2 cell cycle delay and increased cell susceptibility to apoptosis.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Anti-Bacterial Agents / pharmacology
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Antibiotics, Antineoplastic / pharmacology
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Antimetabolites, Antineoplastic / pharmacology
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Apoptosis
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Carrier Proteins*
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Cell Cycle / genetics
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Cell Cycle / physiology
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Cell Cycle Proteins*
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclin-Dependent Kinases / metabolism
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Cyclins / genetics*
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Cyclins / metabolism*
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DNA-Binding Proteins*
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Doxorubicin / pharmacology
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E2F Transcription Factors
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E2F1 Transcription Factor
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Gene Expression Regulation, Neoplastic
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Genes, p53
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Humans
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Methotrexate / pharmacology
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Osteosarcoma / drug therapy*
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Osteosarcoma / genetics*
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Osteosarcoma / metabolism
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Phosphorylation
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Quinazolines / pharmacology
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Retinoblastoma Protein / metabolism
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Retinoblastoma-Binding Protein 1
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Tetracycline / pharmacology
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Tetrahydrofolate Dehydrogenase / genetics
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Thiophenes / pharmacology
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Thymidylate Synthase / genetics
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Transcription Factor DP1
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Transcription Factors / metabolism*
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Tumor Cells, Cultured
Substances
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Anti-Bacterial Agents
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Antibiotics, Antineoplastic
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Antimetabolites, Antineoplastic
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CDKN1A protein, human
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Carrier Proteins
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Cell Cycle Proteins
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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DNA-Binding Proteins
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E2F Transcription Factors
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E2F1 Transcription Factor
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E2F1 protein, human
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Quinazolines
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Retinoblastoma Protein
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Retinoblastoma-Binding Protein 1
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Thiophenes
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Transcription Factor DP1
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Transcription Factors
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Doxorubicin
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Tetrahydrofolate Dehydrogenase
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Thymidylate Synthase
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Cyclin-Dependent Kinases
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Tetracycline
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raltitrexed
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Methotrexate