Abstract
UCN-01, a protein kinase C/cyclin-dependent kinase inhibitor, suppressed thymidylate synthase (TS) protein expression in a dose-dependent manner with near complete suppression at 1 microM after a 24-h exposure in human gastric cancer cell line SK-GT5. Other protein kinase C/cyclin-dependent kinase inhibitors, including flavopiridol and safingol, had a similar effect on TS protein expression, but to a lesser degree. Moreover, UCN-01 repressed the induction of TS after 5-fluorouracil (FU) exposure by 90-95% and significantly enhanced the induction of apoptosis by FU from 4-8% with either FU or UCN-01 alone to 46+/-1% (P < 0.005 versus either single drug, reverse sequence, or the combination) when UCN-01 was given after FU. The effect of UCN-01 on TS was associated with a dose-dependent suppression of the E2F-1 protein, a transcriptional activator of TS. Northern blot analysis revealed that TS mRNA levels decreased gradually as the concentration of UCN-01 increased, but that E2F-1 mRNA levels remained relatively unchanged. UCN-01 may provide a novel way to enhance cellular sensitivity toward FU by means of suppressing TS expression mediated mainly by down-regulation of E2F-1.
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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Alkaloids / administration & dosage
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Alkaloids / pharmacology*
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Antimetabolites, Antineoplastic / administration & dosage
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Antimetabolites, Antineoplastic / pharmacology*
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Antineoplastic Combined Chemotherapy Protocols / pharmacology*
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Apoptosis / drug effects*
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Carrier Proteins*
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Cell Cycle Proteins*
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Cyclin-Dependent Kinases / antagonists & inhibitors
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DNA-Binding Proteins*
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Down-Regulation / drug effects
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Drug Administration Schedule
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Drug Synergism
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E2F Transcription Factors
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E2F1 Transcription Factor
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Enzyme Inhibitors / administration & dosage
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Enzyme Inhibitors / pharmacology*
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Fluorouracil / administration & dosage
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Fluorouracil / pharmacology*
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Gene Expression / drug effects
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Humans
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Protein Kinase C / antagonists & inhibitors
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Retinoblastoma-Binding Protein 1
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Staurosporine / analogs & derivatives
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Stomach Neoplasms / drug therapy
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Stomach Neoplasms / enzymology
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Stomach Neoplasms / metabolism
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Thymidylate Synthase / biosynthesis*
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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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Alkaloids
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Antimetabolites, Antineoplastic
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Carrier Proteins
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Cell Cycle Proteins
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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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Enzyme Inhibitors
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Retinoblastoma-Binding Protein 1
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Transcription Factor DP1
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Transcription Factors
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7-hydroxystaurosporine
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Thymidylate Synthase
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Protein Kinase C
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Cyclin-Dependent Kinases
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Staurosporine
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Fluorouracil