Figure 4. Effects of glucosamine (GlcN) on epidermal growth factor (EGF)-induced cell-cycle progression in human retinal pigment epithelial cell line (ARPE-19) cells. A: ARPE-19 cells were deprived of serum for 24 h and then harvested at the indicated times after stimulation with 10 ng/ml EGF with or without the addition of GlcN. B: ARPE-19 cells were synchronized in early S phase by serum deprivation and aphidicolin treatment and harvested at the indicated times after release from the aphidicolin block by stimulation with 10 ng/ml EGF with or without the addition of GlcN. The percentages of cells in the G₀–G₁, S, and G₂–M phases were determined. The data are the means±SD of three independent experiments.