Chang Wei-Hsiu, Tien Chih-Liang, Chen Tzu-Jung, Nukina Nobuyuki, Hsieh Mingli
Department of Life Science, Tunghai University, Taichung, Taiwan, ROC.
Neurosci Lett. 2009 Apr 24;454(2):152-6. doi: 10.1016/j.neulet.2009.03.004. Epub 2009 Mar 5.
Machado-Joseph disease is an autosomal dominant spinocerebellar degeneration caused by the expansion of a polyglutamine tract within the gene product, ataxin-3. We have previously shown that increased oxidative stress and decreased expression of Hsp27 may be contributory factors to the disease progression. In this study, we utilized neuroblastoma SK-N-SH cells stably transfected with full-length expanded ataxin-3 to further investigate the mechanism(s) resulting in the decreased expression of Hsp27. Results from 35S-methionine pulse-chase labeling and protein degradation assays revealed that decreased Hsp27 in mutant MJD cells is due to defects in protein synthesis. Our results further demonstrated that Hsp27 degradation is independent of the proteasome degradation pathway. In addition, we showed that overexpression of Hsp27 desensitizes mutant MJD cells to apoptotic stress. Taken together, these findings provide the first evidence that expanded ataxin-3 interferes with Hsp27 synthesis, which may contribute to the impairment of the cells' ability to respond to stresses and trigger the progression of this late-onset disease.
马查多-约瑟夫病是一种常染色体显性遗传性脊髓小脑变性疾病，由基因产物ataxin-3内的多聚谷氨酰胺序列扩增所致。我们之前已经表明，氧化应激增加和Hsp27表达降低可能是疾病进展的促成因素。在本研究中，我们利用稳定转染全长扩增ataxin-3的神经母细胞瘤SK-N-SH细胞，进一步研究导致Hsp27表达降低的机制。35S-甲硫氨酸脉冲追踪标记和蛋白质降解试验结果表明，突变型马查多-约瑟夫病（MJD）细胞中Hsp27降低是由于蛋白质合成缺陷所致。我们的结果进一步证明，Hsp27降解与蛋白酶体降解途径无关。此外，我们还表明，Hsp27的过表达使突变型MJD细胞对凋亡应激不敏感。综上所述，这些发现首次证明扩增的ataxin-3会干扰Hsp27的合成，这可能导致细胞应对应激能力受损，并引发这种迟发性疾病的进展。
