Ornatsky O I, Connor M K, Hood D A
Department of Biology, York University, North York, Ontario, Canada.
Biochem J. 1995 Oct 1;311 ( Pt 1)(Pt 1):119-23. doi: 10.1042/bj3110119.
Molecular chaperones and cytosolic stress proteins are actively involved in the stabilization, import and refolding of precursor proteins into mitochondria. The purpose of the present study was to evaluate the relationship between mitochondrial content under steady-state conditions, and during the induction of organelle biogenesis, with the expression of stress proteins and mitochondrial chaperonins. A comparison of steady-state levels of mitochondrial enzyme activity [cytochrome c oxidase (CYTOX)] with chaperonin levels [the heat-shock protein HSP60, the glucose-regulated protein GRP75 (mtHSP70)] in striated muscles possessing a wide range of oxidative capacities revealed a proportional expression between the two. This relationship was disrupted by chronic contractile activity brought about by 10 days of 10 Hz stimulation of the tibialis anterior (TA) muscle, which induced 2.4-fold increases in CYTOX activity, but 3.2- and 9.3-fold increases in HSP60 and GRP75 respectively. The inducible stress protein HSP70i was detected at low levels in control TA muscle, and was increased 9.6-fold by chronic contractile activity, to values comparable with those found in the unstressed soleus muscle. This increase occurred in the absence of changes in type I MHC levels, indicating independent regulation of these genes. Despite the increases in HSP60 and HSP70i proteins, contractile activity did not alter their respective mRNA levels, illustrating post-transcriptional mechanisms of gene regulation during contractile activity. In contrast, the mRNA levels encoding the co-chaperonin CPN10 were increased 3.3-fold by contractile activity. Thus, the expression of individual mitochondrial chaperonins is independently regulated and uncoordinated. The extent of the induction of these stress proteins and chaperonins by contractile activity exceeded that of membrane enzymes (e.g. CYTOX). It remains to be determined whether this marked induction of proteins comprising part of the protein import machinery is beneficial for the translocation of enzyme precursors into the mitochondria during conditions of accelerated biogenesis.
分子伴侣和胞质应激蛋白积极参与前体蛋白在线粒体内的稳定、导入和重折叠过程。本研究的目的是评估稳态条件下以及细胞器生物发生诱导过程中线粒体含量与应激蛋白和线粒体伴侣蛋白表达之间的关系。对具有广泛氧化能力的横纹肌中线粒体酶活性[细胞色素c氧化酶（CYTOX）]的稳态水平与伴侣蛋白水平[热休克蛋白HSP60、葡萄糖调节蛋白GRP75（mtHSP70）]进行比较，结果显示二者呈比例表达。这种关系被胫骨前肌（TA）肌肉10天10赫兹刺激所引发的慢性收缩活动破坏，该刺激使CYTOX活性增加了2.4倍，但HSP60和GRP75分别增加了3.2倍和9.3倍。在对照TA肌肉中可检测到低水平的诱导型应激蛋白HSP70i，慢性收缩活动使其增加了9.6倍，达到与未受应激的比目鱼肌相当的值。这种增加发生在I型肌球蛋白重链水平未发生变化的情况下，表明这些基因受到独立调控。尽管HSP60和HSP70i蛋白增加，但收缩活动并未改变它们各自的mRNA水平，这说明收缩活动期间基因调控存在转录后机制。相反，编码共伴侣蛋白CPN10的mRNA水平因收缩活动而增加了3.3倍。因此，单个线粒体伴侣蛋白的表达受到独立调控且不协调。收缩活动对这些应激蛋白和伴侣蛋白的诱导程度超过了膜酶（如CYTOX）。在生物发生加速的情况下，构成蛋白质导入机制一部分的这些蛋白的显著诱导是否有利于酶前体转运到线粒体中，仍有待确定。
