An array of cyclins, cyclin dependent kinases (cdk), and cdk inhibitors synthesized at different transitional stages of the cell cycle, operate in concert to propel cells through regulatory checkpoints during cell division. Cells exhibiting unscheduled expression of these molecules either fail to progress through cell cycle and undergo apoptosis, or lose cell cycle control and proliferate indefinitely as in many tumor cells. Initial stimulation of bone marrow CD34+ cells residing in G0 (G0CD34+ cells) with IL3 only induces growth arrest in a fraction of these cells, most likely via disruption of cell cycle regulatory processes (Ladd et al. Blood 90:658, 1997). In order to examine the role of cyclins, cdk, and cdk inhibitors in cell cycle regulation of primitive hematppoietic progenitor cells (HPC) proliferating in response to different cytokine stimuli, cultured GoCD34+ cells were monitored for expression of a panel of cell cycle regulatory proteins. A fraction of freshly isolated GrjCD34+ cells were stained at time zero with 7AAD and a panel of monoclonal antibodies against cyclins, cdk, and cdk inhibitors. The remaining cells were maintained in short-term cultures in the presence of either SCF, FL and TPO, or IL3 and GM-CSF. On day 4, cells were harvested, stained with the same panel of monoclonal antibodies and 7AAD and analyzed. The only regulatory molecule expressed by a high percentage of freshly isolated GoCD34+ cells was p27kiP1, suggesting possibly the role of this inhibitor in maintaining primitive HPC in mitotic quiescence. The exit from GO into active phases of cell cycle in the presence of SCF, FL, and TPO was associated with an increase in the percentage of cells expressing cyclins D, E and A along with cdk2 and 3, while the percentage of p27kiP1 positive cells decreased. Expression of p21 on d4 was not appreciably different in these cultures than that observed on dO. However, cells maintained in IL3 and GM-CSF displayed a sharp rise in the percentage of cells expressing p21 concomitant with maintenance or an increase in cells expressing p27kiP1. In addition, the increase in cells expressing cyclin D was mostly restricted to those in GQ/GI phases of cell cycle, suggesting possible growth arrest of these cells in GV These preliminary results shed some light on operative cell cycle regulation proteins in primitive HPC and mechanisms of cell cycle progression following cytokine stimulation.
|Original language||English (US)|
|Number of pages||1|
|State||Published - Dec 1 1998|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology
- Cancer Research