Anti-apoptotic effects of dexamethasone and phosphoinositide 3-kinase inhibitors on PUMA-mediated apoptosis of lovastatin-treated cells

[Speaker] Jae Won Choi:1
[Co-author] Jichang Seong:1, Junghan Yoon:2, Hyoshik Shin:1
1:Department of Pharmacology, Yonsei University Wonju College of Medicine, Korea, 2:Department of Internal Medicine, Yonsei University Wonju College of Medicine, Korea

Lovastatin belongs to the statin family of drugs used to treat hypercholesterolemia. Statins inhibit 3-hydroxy-3-methyl glutaryl-coenzyme A reductase, the rate-limiting enzyme of cholesterol biosynthesis, to block mevalonate biosynthesis. Mevalonate is a precursor of various metabolic intermediates such as isopentenyl pyrophosphate, geranyl pyrophosphate, farnesyl pyrophosphate, geranylgeranyl pyrophosphate, squalene, lanosterol, dolichol, and ubiquinon, which are responsible for maintaining normal cellular functions. In our previous study, we have reported that lovastatin induces PUMA-dependent apoptosis in C6 glioma cells. In this study, we examined the effects of glucocorticoid and/or phosphoinosidte (PI)-3-kinase inhibitor in lovastatin-induced apoptosis in C6 glioma cells. Trypan blue exclusion assay showed that lovastatin induced cell death in approximately 40% and 70% of cells at 36 and 48 hours, respectively. Lactate dehydrogenase assay showed that dexamethasone, wortmannin, or LY294002 significantly attenuated lovastatin-induced apoptosis in a dose-dependent manner until 48 hours after lovastatin treatment. When cells were co-treated with both dexamethasone and PI3-kinase inhibitor, lovastatin-induced apoptosis was further attenuated. In fact, lovastatin-induced apoptosis was almost completely suppressed in the presence of dexamethasone (100 nM) and wortmannin (30 uM) 48 hours after treatment. Serum deprivation, which is similar to lovastatin treatment, has also been reported to induce PUMA-mediated apoptosis in C6 cells. In our study, we found that serum deprivation-induced cell death was suppressed by dexamethasone, but not by wortmannin. Interestingly, qPCR data showed that the lovastatin-induced increase of PUMA mRNA levels was further enhanced by either wortmannin or LY294002 treatment; however, it was not affected by dexamethasone treatment. As wortmannin or LY294002 alone increased the levels of PUMA mRNA significantly, it appeared that lovastatin and the PI-3 kinase inhibitor induced PUMA expression in a summative manner via different mechanisms. Our data suggest that dexamethasone and PI-3 kinase inhibitors could prevent lovastatin-induced apoptosis not by suppressing the increase of PUMA expression, but by activating unique anti-apoptotic pathways.
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