p21^CIP1/WAF1 degradation is via the proteasomal pathway. (A-H) The effect of 311 on p21^CIP1/WAF1 expression in MCF-7 cells in the presence or absence of the proteasomal inhibitor MG132 and the protein synthesis inhibitor cycloheximide (CHX). MCF-7 cells were incubated for 0.5 to 24 hours at 37°C with: (A) control medium (Con); (B) 311 (25 μM); (C) CHX (10 μg/mL); (D) 311 (25 μM) and CHX (10 μg/mL); (E) MG132 (20 μM); (F) 311 (25 μM) and MG132 (20 μM); (G) MG132 (20 μM) and CHX (10 μg/mL); or (H) 311 (25 μM), MG132 (20 μM), and CHX (10 μg/mL). (I) Densitometric analysis of the results in panels A-H. Cells were harvested and Western blot analysis was performed. Results shown are from a representative experiment of 3 performed.