Effects of SAHA or SB and bortezomib on cell cycle and signaling protein K562 cells. (A) K562 cells were exposed to 1.5 μM SAHA ± 4.5 nM bortezomib for 24 hours, after which the expression of p21^CIP1, cyclin D₁, total pRb, and underphosphorylated pRb were examined by Western blot as described in “Materials and methods.” CF indicates cleavage fragment. Each lane contained 25 μg protein. (B) Following treatment with SAHA ± bortezomib as shown in panel A, expression of Raf, phospho-MEK1/2 and phospho-ERK1/2, phospho-JNK, total JNK, phospho-p38 MAPK, and total p38 was monitored as in panel A. Each lane contained 25 μg protein; blots were stripped and reprobed for tubulin to ensure equivalent loading and transfer. An additional 2 studies yielded equivalent results.