Serum stimulation of stationary human glia and glioma cells in culture

Stationary cell cultures can be stimulated to re-enter the cell cycle by giving medium containing fresh serum. The mechanism for this initiation was studied in normal human glia and neoplastic glioma cells in order to demonstrate any differences between normal and neoplastic cells regarding the kinetics of their march through G 1 into the S phase of the cell cycle. Glia cells were found to demand at least 12 h of serum stimulation to enter the cell cycle and were committed to DNA synthesis about 4 h prior to the actual onset of this synthesis. On the other hand, as little as l h of serum stimulation induced DNA synthesis in a fraction of glioma cells and these malignant cells were committed during the largest part of the prereplicative phase. This difference in commitment kinetics could not be explained by differences in cell cycle parameters or medium deficiencies and is considered to reflect a part of the fundamental difference between normal and neoplastic cells as regards their growth control.