Hypoxic Cell Cycle Arrest by PHD3 Inhibition Figure 5. PHD3 inhibition causes a block in G1 to S-phase transition in hypoxia. (A) SCC2 cells were transfected with the indicated siRNAs and exposed to normoxia (21% O2) or hypoxia (1% O2) for 24 to 48 hours. Samples were and stained with PI and analyzed with FACS. The data was plotted as cell cycle histograms (FL2-A vs. counts). The cells exposed to PHD3 siRNA showed an increase in the size of G1 population and a decrease in the S and G2+M populations relative to control. The histograms show representative examples. (B) Quantification of cells in G1 phase after exposure to the indicated siRNAs and hypoxic treatments. Data from three independent experiments are shown as fold change vs. control (siScr). Means and SD are shown. (C) Quantification of cells in the S phase after exposure to the indicated siRNAs and hypoxic treatments. Data from three independent experiments are shown as fold change vs. control (siScr). Means and SD are shown. (D) Calculation of the relative sizes of the G1 to S phase from three independent experiments. (E) HeLa cells were treated with the indicated siRNAs followed by synchronization of the cells. After PLoS ONE | www.plosone.org 7 November 2011 | Volume 6 | Issue 11 | e27112