FIG. 4.

Proteasome inhibitors block FN-induced down-regulation of p21^CIP1 and p27^KIP1. (A) ECV 304 cells were pretreated with lactacystin, β-lactone, or LLnL or with the dimethyl sulfoxide (DMSO) vehicle as a control and then plated on FN for the indicated times. p21^CIP1, p27 ^KIP1, and actin protein levels were analyzed by Western blotting. (B) ECV 304 cells were allowed to attach to FN or P-L-L, and then the levels of cyclin E and p53 were examined by Western blotting. The levels of p21^CIP1 were used as a comparison and determined with anti-p21^CIP1 MAb SX118.