Proliferation of the growth factor-dependent human hematopoietic cell lines UT7/Epo and M-07e rely upon the stimulation of the cell cycle by cytokines. When these cells are starved of their dependent growth cytokine, they are held up at one of the checkpoints within the cell cycle. These specific checkpoints can be identified using propidium iodide and flow . cytometry. UT7/Epo cells starved of Epo are growth arrested and accumulate in S-phase suggesting that the S to O2+M checkpoint is the site of Epo action. On the other hand, M07e cells starved of GM-CSF accumulate in GO/G1 and up to 65 % of the cells are apoptotic at 24hrs. The number of UT7/Epo cells undergoing apoptosis increases to 75 % at 48 hours, while no apoptotic UTTVEpo cells are observed at 24 hours and only 32% at 48 hours. Approximately 24 hours after readdition of Epo to starved cells, UT7/Epo cells enter G2+M and their cycle normalizes by 48 hours. The same kinetics of response occur when GM-CSF is added to starved M-07e. Within 24 hrs the cells progress into S-phase arid through to G2+M. When other cytokines, such as IL-3, SCF and Tpo, which stimulate M-07e to proliferate, are added to starved M07e, the cells enter S-phase and progress through to G2+M in the same time frame as they do with GM-CSF. However, Tpo, which is a weak inducer of proliferation, did not decrease the percentage of apoptotic cells to the same degree as the other cytokines. SCF will also induce proliferation of UT7/Epo cells and addition to Epostarved cells has the same affect as adding Epo, i. e. , the cells progress into G2+M. Protein expression of cyclin B, cyclin D3, cdk , cdk 4 and cdc2 detected by Western blots in lysates of UT7/Epo and M-07e starved of cytokines showed that except for cdk , the amount of protein decreased between 0 and 24 hours of cytokine starvation. Further experiments are required to determine if it is the activation state of these cyclins that is responsible for the cytokine starvation results. In conclusion, intrinsic properties unique to each cell line rather than growth factors determine the regulatory criteria for cell cycle progression.
|Original language||English (US)|
|Number of pages||1|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology
- Cancer Research