UCN-01 suppresses thymidylate synthase gene expression and enhances 5-fluorouracil-induced apoptosis in a sequence-dependent manner.
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.
Hsueh
C T
CT
Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Kelsen
D
D
Schwartz
G K
GK
D000470:Alkaloids / Q000008:administration & dosage / Q000494:pharmacology*; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004268:DNA-Binding Proteins; D015536:Down-Regulation / Q000187:drug effects; D004334:Drug Administration Schedule; D004357:Drug Synergism; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D005472:Fluorouracil / Q000008:administration & dosage / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D056465:Retinoblastoma-Binding Protein 1; D019311:Staurosporine / Q000031:analogs & derivatives; D013274:Stomach Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism; D013940:Thymidylate Synthase / Q000096:biosynthesis* / Q000235:genetics; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000470:Alkaloids; D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D004791:Enzyme Inhibitors; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; C054852:7-hydroxystaurosporine; D013940:Thymidylate Synthase; D011493:Protein Kinase C; D018844:Cyclin-Dependent Kinases; D019311:Staurosporine; D005472:Fluorouracil