Department of Medical Biology, Medical School, University of Pécs, Pécs, Hungary H-7643, Pécs, Szigeti út 12., Hungary.
Brain Res. 2013 Jul 3;1520:70-9. doi: 10.1016/j.brainres.2013.05.015. Epub 2013 May 20.
In this work we tried to identify mechanisms that could explain how chemical inhibition of heat-shock protein 90 reduces nerve growth factor signaling in rat pheochromocytoma PC12 cells. Geldanamycin is an antibiotic originally discovered based on its ability to bind heat-shock protein 90. This interaction can lead to the disruption of heat-shock protein 90-containing multimolecular complexes. It can also induce the inhibition or even degradation of partner proteins dissociated from the 90 kDa chaperone and, eventually, can cause apoptosis, for instance, in PC12 cells. Before the onset of initial apoptotic events, however, a marked decrease in the activity of extracellular signal-regulated kinases ERK 1/2 and protein kinase B/Akt can be observed together with reduced expression of the high affinity nerve growth factor receptor, tropomyosine-related kinase, TrkA, in this cell type. The proteasome inhibitor MG-132 can effectively counteract the geldanamycin-induced reduction of TrkA expression and it can render TrkA and ERK1/2 phosphorylation but not that of protein kinase B/Akt by nerve growth factor again inducible. We have found altered intracellular distribution of TrkA in geldanamycin-treated and proteasome-inhibited PC12 cells that may, at least from the viewpoint of protein localization explain why nerve growth factor remains without effect on protein kinase B/Akt. The lack of protein kinase B/Akt stimulation by nerve growth factor in turn reveals why nerve growth factor treatment cannot save PC12 cells from geldanamycin-induced programmed cell death. Our observations can help to better understand the mechanism of action of geldanamycin, a compound with strong human therapeutical potential.
在这项工作中，我们试图确定能够解释化学抑制热休克蛋白 90 如何降低大鼠嗜铬细胞瘤 PC12 细胞中神经生长因子信号的机制。格尔德霉素是一种最初基于其结合热休克蛋白 90 的能力而被发现的抗生素。这种相互作用可以导致热休克蛋白 90 包含的多分子复合物的破坏。它还可以诱导与 90 kDa 伴侣蛋白解离的伴侣蛋白的抑制甚至降解，最终，例如，在 PC12 细胞中导致细胞凋亡。然而，在初始凋亡事件发生之前，可以观察到细胞外信号调节激酶 ERK 1/2 和蛋白激酶 B/Akt 的活性明显降低，并且在这种细胞类型中高亲和力神经生长因子受体，原肌球蛋白相关激酶 TrkA 的表达降低。蛋白酶体抑制剂 MG-132 可以有效地抵消格尔德霉素诱导的 TrkA 表达降低，并且可以使 TrkA 和 ERK1/2 磷酸化，但不能使蛋白激酶 B/Akt 再次被神经生长因子诱导磷酸化。我们发现，在格尔德霉素处理和蛋白酶体抑制的 PC12 细胞中，TrkA 的细胞内分布发生改变，这至少从蛋白质定位的角度解释了为什么神经生长因子对蛋白激酶 B/Akt 仍然没有作用。反过来，神经生长因子缺乏对蛋白激酶 B/Akt 的刺激揭示了为什么神经生长因子处理不能使 PC12 细胞免受格尔德霉素诱导的程序性细胞死亡。我们的观察结果可以帮助更好地理解格尔德霉素的作用机制，格尔德霉素是一种具有强大人类治疗潜力的化合物。
