Only on Jurkat cell line it was observed, after 72 h of culture, a mild, not significant, dose-dependent increase of cells in G0 phase associated with a decrease of G1 and S compartment and with a nonsignificant increase of sub-G0/1 (Figure 2).
Data presented in our study demonstrated that TR causes in leukemia models a dose-dependent increase of cells in G0 phase and a decrease in both G1 and S phases.
Among them CDK4 and CDK6 are responsible for helping cells getting out from
G0 phase and into G1 phase [56, 57]; meanwhile CDK2 plays its role in G1 phase [58].
The nuclear antigen AgKi67 (MiB-1) is a protein in all phases of the cell cycle except the
G0 phase, and has a direct relationship with the growth rate of a cell population.
In the above equations, [beta](N) (equation (3)) measures the rate of cell re-entry into proliferation, [[beta].sub.0] in is the maximal rate of cell transit from resting phase to S phase, n measures the sensitivity of the rate of cell transit from
G0 phase to S phase, and [theta] is the G0 stem cell population at which the rate of cell movement from G0 into proliferation is one-half of its maximal value.
Also, PBMCs were evaluated for cell cycle distribution after exposure to Pd-NP and Pd(IV), in absence of PHA stimulation; in no case were these compounds found to induce cell cycle initiation and all cells remained in the
G0 phase (data not shown).
Prior to differentiation, cells are arrested at the G1/S phase and enter the
G0 phase without passing the cell cycle restriction point.
Although malignant gliomas grow rapidly, more than 90% of the malignant cells in a GBM are in
G0 phase, or resting (Salcman, 1990), so that only a small portion of cells are susceptible to cell cycle-specific agents.
It is believed that adult stem cells mainly exist in a state of nonproliferation, reversible cell cycle-arrest, known as quiescence (
G0 phase) [25].
