Figure 1. Cyclin E1 and E2 have discordant cell cycle expression in cancer cells. (A) Breast cancer and normal/immortalized cell line lysates were immunoblotted for cyclins E1 and E2, p21^Waf1/Cip1, p27^Kip1 and GAPDH. (B) Densitometry was performed on the levels of cyclins E1 and E2, and normalized to expression of GAPDH. (C) Linear regression identified a negative correlation between the expression of cyclin E1 and cyclin E2 (y = -1.0426x + 22.999, R² = 0.4591; p < 0.0648). (D) T-47D cells were synchronized with HU, released into the cell cycle, and matched lysates and flow cytometry samples collected 0–15h post release. Lysates were immunoblotted as indicated, and densitometry performed on cyclin E1 and E2 expression normalized to GAPDH expression. Cell cycle distribution was analyzed by propidium iodide staining. Data are from duplicate experiments and error bars represent range between replicates. (E) MCF-7 cells in G₀/G₁ phase (ICI 182780 arrest) and early S phase (estrogen stimulated) were analyzed for DNA content by propidium iodide staining (PI) and expression of cyclins E1 and E2 by flow cytometry.