Figure 4.

The DNA synthesis inhibitor aphidicolin prevents the 5-aza-dC induced degradation of DNMT1. Western blots of DNMT1 and GAPDH (loading control) in 5-aza-dC treated HCT116 cells (A) and SW620 cells (B) to show the effects of 5-aza-dC on its own (top panels) as compared with cells that had been treated with the DNA synthesis inhibitor aphidicolin 20 μg/ml for 24 h prior to treatment with 5-aza-dC (bottom panels). (C) Western blot and (D) cell-cycle analysis to show DNMT1 levels at various stages after synchronization and release from an aphidicolin block. DNMT1 protein levels are prominent in synthesis, and markedly reduced in G1 and G2 phases of the cell cycle. (E) Cell-cycle analysis of HCT116 cells exposed to the indicated concentrations of 5-aza-dC for 24 h.