Abstract
Camptothecin (CPT) traps covalent DNA topoisomerase I-linked DNA single-strand breaks (cleavable complexes). To determine the differences in DNA damage signalling leading to differential sensitivity to CPT, two human colon cancer cell lines, SW620 and KM12, with nonfunctional p53 and the same level of topoisomerase I cleavable complex formation but differential sensitivity to CPT (Cancer Res. 56:4430-7; 1996) were studied. The levels of mRNA expression of DNA damage-inducible or death-related genes were measured at different times after CPT treatment. KM12 cells exhibited 3-fold higher basal levels of BCL-2 mRNA. Consistently, secondary DNA fragmentation, quantitated using a filter elution assay, was detected 24 h later and was 2-4-fold lower in KM12 cells than in SW620 cells. No induction of BAX was detected in either cell line. Consistent with the absence of functional p53, p21CIP1/WAF1 and GADD45 genes were not induced within the first 24 h. However, in SW620 cells, both mRNA levels were increased more than 10-fold at 48 h. The BCL-2-related gene MCL-1 and topoisomerase II mRNA were induced at 24 h, and topoisomerase I mRNA levels increased 3-fold at 48 h, only in SW620 cells. We conclude that cellular response to CPT-induced DNA damage can involve p53-independent pathways leading to the induction of p53-effector genes. Induction of these genes at the onset of apoptosis is associated with CPT sensitivity.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Antineoplastic Agents, Phytogenic / pharmacology*
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Apoptosis / drug effects
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Camptothecin / pharmacology*
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Colonic Neoplasms / genetics
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Colonic Neoplasms / pathology*
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins / biosynthesis*
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Cyclins / genetics
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DNA Damage*
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DNA Fragmentation
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DNA Topoisomerases, Type II / biosynthesis*
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DNA Topoisomerases, Type II / genetics
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DNA, Neoplasm / drug effects*
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DNA, Neoplasm / genetics
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Drug Resistance, Neoplasm / genetics
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Enzyme Induction / drug effects
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Enzyme Inhibitors / pharmacology*
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GADD45 Proteins
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Gene Expression Regulation, Neoplastic / drug effects*
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Genes, p53*
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Humans
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Intracellular Signaling Peptides and Proteins
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins / antagonists & inhibitors
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Neoplasm Proteins / biosynthesis*
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Neoplasm Proteins / genetics
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Protein Biosynthesis*
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Proteins / genetics
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Proto-Oncogene Proteins / biosynthesis
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins c-bcl-2*
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Topoisomerase I Inhibitors*
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Transcriptional Activation
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Tumor Cells, Cultured
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bcl-2-Associated X Protein
Substances
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Antineoplastic Agents, Phytogenic
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BAX protein, human
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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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DNA, Neoplasm
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Enzyme Inhibitors
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Intracellular Signaling Peptides and Proteins
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins
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Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Topoisomerase I Inhibitors
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bcl-2-Associated X Protein
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DNA Topoisomerases, Type II
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Camptothecin