Effect of camptothecin on mitogenic stimulation of human lymphocytes: Involvement of DNA topoisomerase I in cell transition from G0 to G1 phase of the cell cycle and in DNA replication
✍ Scribed by Silvia Bruno; Walter Giaretti; Zbigniew Darzynkiewicz
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 929 KB
- Volume
- 151
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
The possible involvement of DNA topoisomerase I in cell transition from C , to G , and in progression through the cell cycle was studied by estimating the ability of human peripheral blood lymphocytes to undergo mitogenic stimulation in the presence of the topoisomerase I inhibitor camptothecin (CAM). Exposure of quiescent Go lymphocytes to up to 3 pM CAM for 24 h had no significant effect o n their ability to subsequently undergo mitogenic stimulation in the presence of phytohemagglutinin (PHA); higher doses of CAM, although not immediately cytotoxic, impaired the mitogenic response. Stimulation of lymphocytes with PHA in the presence of s 1.5 pM CAM resulted in unperturbed transition of these cells from G , to G, characterized as an increase in cellular rKNA content, appearance of interleukin-2 receptor, and, after removal of CAM, response to interleukin-2 by entering S phase of the cell cycle. However, lymphocytes were prevented from entering S phase in the presence of CAM at a concentration of 30 nM, and their rate of progression through S was minimal even at CAM concentration as low as 3 nM. When cycling lymphocytes (48 h after stimulation by PHA) were treated with CAM, the cell progression through S and C, was also very sensitive to the inhibitor: the cells were "frozen" in Sand G, at 3 6 n M CAM. These cells died within 24 h; their selective loss from the cultures (with only G,/G, cells remaining