Effect of GM-CSF on Stat 1, Stat 5, phosphorylated Stat 5, and cyclin D2 protein levels and on the progression of OCIM2 cells through the cell cycle. Stat 1, Stat 5, and phosphorylated Stat 5 (A) and cyclin D2 (B) proteins were detected by Western immunoblotting before and after OCIM2 cells were incubated with 0.025 μg/mL GM-CSF for 5, 10, 15, 20, and 30 minutes. Levels of procaspase 3 were measured to verify that procaspase 3 levels were up-regulated under the same conditions. A band of β-actin, demonstrating equal protein loading, is presented as a loading control. (C) Growth factor–deprived OCIM2 cells were incubated with 0.025 μg/mL GM-CSF for 8 hours and the cell cycle status of cell samples was analyzed at different time points. As shown, the fractions of cells entering S and G₂M phases increase over time; then they decrease and the fraction of cells in G₀/G₁ phase of the cell cycle increases again. Representative data from 3 different experiments are shown.