Bcl-xL modulates apoptosis induced by anticancer drugs and delays DEVDase and DNA fragmentation-promoting activities.
Using an episomal eucaryotic expression vector, we derived three stable transfected human leukemic U-937 variant lines showing differential expression of the Bcl-xL protein. Preventive effect of Bcl-xL on cell death induced by various concentrations of camptothecin (DNA topoisomerase I inhibitor; CPT) was observed in the three lines with most pronounced effect in cells containing the highest level of Bcl-xL expression. These results show that increased cell death protection by Bcl-xL is correlated with its level of expression. The extent of DNA strand break formation and DNA synthesis inhibition following CPT treatments was similar in control and transfected U-937 cells, suggesting that Bcl-xL acts downstream of CPT-DNA topoisomerase I-mediated DNA strand breaks. Modulation of cell death by Bcl-xL was also observed in cells treated with etoposide, vinblastine, paclitaxel, and cisplatinum (II) diammine dichloride. To define whether Bcl-xL functions downstream or upstream of apoptogenic proteolytic cascade activation, we compared kinetics of DNA fragmentation in treated cells with kinetics of caspase 1-like, caspase 3-like, and N-tosyl-L-phenylalanylchloromethyl ketone (TPCK)-sensitive activities. In CPT-treated U-937 cells, caspase 3-like and TPCK-sensitive activities promoting DNA fragmentation in a cell-free system were detected much more rapidly in extracts obtained from CPT-treated U-937 cells compared to those obtained from CPT-treated U-937-Bcl-xL variant cells. These results suggest that Bcl-xL delays their activation that correlates with the occurrence of DNA fragmentation. Addition of recombinant Bcl-xL in extracts containing DEVDase and TPCK-sensitive activities did not inhibit these activities, suggesting that Bcl-xL acts primarily upstream of their activation in the apoptotic process. Taken together, these results suggest that Bcl-xL is a primary checkpoint that can block or delay transmission of cell death signals emerging from DNA damage and prevents activation of an apoptogenic proteolytic cascade.
Schmitt
E
E
Hospital Research Center of University of Montreal (CHUM), Montreal Cancer Institute, Quebec, Canada.
Cimoli
G
G
Steyaert
A
A
Bertrand
R
R
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002166:Camptothecin / Q000494:pharmacology*; D002474:Cell-Free System; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D053938:DNA Fragmentation / Q000187:drug effects*; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute; D009842:Oligopeptides / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D014108:Tosylphenylalanyl Chloromethyl Ketone / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D051020:bcl-X Protein
D000972:Antineoplastic Agents, Phytogenic; C494811:BCL2L1 protein, human; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; D019253:Proto-Oncogene Proteins c-bcl-2; D015842:Serine Proteinase Inhibitors; C099158:acetyl-aspartyl-glutamyl-valyl-aspartal; D051020:bcl-X Protein; C096429:L 709049; D014108:Tosylphenylalanyl Chloromethyl Ketone; D010450:Endopeptidases; D010447:Peptide Hydrolases; C108711:DEVDase; D002166:Camptothecin