Figure 6
The hyperactive PI3K/Akt signaling is responsible for the resistance of MPM cells to MG132-induced apoptosis. (A) TRAIL and MG132 combination does not affect mRNA expression of the Akt gene in NCI-H28 cells, as indicated by a semi-quantitative RT-PCR at 36 h after treatment with 1 μM MG132, 10 ng/ml TRAIL or MG132 plus TRAIL. Expression of GAPDH is used as an internal control. (B) Simultaneous reduction of both P-Akt and Mcl-1 sensitizes NCI-H28 cells to MG132-induced apoptosis: Western blotting demonstrates that simultaneous reduction of P-Akt by 15 μM LY294002 and Mcl-1 by Mcl-1 siRNA, which results in approximately 50% reduction of Mcl-1 protein expression as determined by quantitative analysis using the online software Image J (B-1), can induce protein cleavages for caspase 3 and PARP in 1 μM MG132-treated NCI-H28 cells, whereas reduction of either P-Akt or Mcl-1 is not effective. Protein cleavage fragments in Western blots are indicated by arrows (B-2).