Figure 5

Inhibition of MEK signaling alleviates the inhibitory effect of cAMP on IR-induced cell death. (A) Cells were cultured in the absence or presence of 50 μM PD 98059 alone (Reh and TK6) or together with 400 μM IBMX (EU-3) for 45 min before treatment with or without 80 μM forskolin (Reh), 200 μM 8-CPT-cAMP (TK6) or 100 μM forskolin (EU-3) for 30 min. Cells were then exposed to 10 Gy IR, harvested after 12 h (EU-3) or 20 h (Reh and TK6) and analyzed for PI uptake by FACS (n = 4). The p values were calculated relative to cells treated with IR only: Reh, *p < .02. TK6, *p < .01, **p < .03. EU-3, *p < .01, **p < .04. The histograms in the right panel depict percent inhibition of IR-induced cell death by forskolin, 8-CPT-cAMP or forskolin and IBMX in the presence or absence of PD 98059. (B) Reh cells were transfected with control siRNA or siRNAs against MEK1 and MEK2. Cells were then treated with or without forskolin (80 μM) for 30 min before exposure to IR (10 Gy). After 20 h, cells were analyzed for PI uptake by FACS (n = 4). *p < .01, **P < .03 relative to cells treated with IR only. The histogram in the right panel depicts percent inhibition of IR-induced cell death by forskolin in cells transfected with control siRNA or MEK1 and MEK2 siRNAs.