Apoptosis Induced by Serum Deprivation of PC12 Cells Is Not Preceded by Growth Arrest and Can Occur at Each Phase of the Cell Cycle
Previous studies have shown that PC12 cells undergo apoptosis (programmed cell death) when deprived of serum. In the present study, we examined the relationship of this death process to the cell cycle. PC12 cell populations synchronized at different, specific phases of the cell cycle exhibit similar kinetics of cell death following deprivation of serum. Flow cytometry analysis was used to examine the levels of apoptotic death in these cell populations in relationship to their progression in the cell cycle during the course of serum deprivation. Such analysis revealed that the cells die during the G0-G1, S, and perhaps G2-M phases and at the G2 to G1 transition. These results, therefore, suggest that the death of synchronized, serum-deprived PC12 cells occurs throughout the cell cycle and is not dependent on growth arrest. Flow cytometry methodology (acridine orange staining), which determines the RNA content of cells in relationship to their position in the cell cycle, was used to address these questions in nonsynchronized cells. These experiments revealed that, upon serum deprivation, an immediate loss of RNA occurred from cells in G1, S, and G2-M phases. This loss is accompanied by a slower appearance of cells with degraded DNA content. These results show that cells from all phases of the cell cycle are damaged upon serum deprivation and thus suggest that the apoptotic cell death of nonsynchronized PC12 cells may occur from each phase of the cell cycle.