Schröder H C, Messer R, Bachmann M, Bernd A, Müller W E
Institut für Physiologische Chemie, Universität, Mainz, F.R.G.
Mech Ageing Dev. 1987 Dec;41(3):251-66. doi: 10.1016/0047-6374(87)90045-5.
In eucaryotic cells, immature mRNA is normally restricted to the nucleus, where it is posttranscriptionally processed to mature mRNA. The intranuclear binding site for both the immature and mature mRNA is thought to be the nuclear matrix which serves as a platform for posttranscriptional RNA maturation and transport. The selectivity of nucleocytoplasmic transport for mature mRNA species seems to be due to the selectivity of the ATP-caused release of mature mRNA from the nuclear matrix; the attachment of immature mRNA to the matrix is not altered in the presence of this nucleotide. Here we show that in the presence of superoxide radical anions (O2-), which are very likely one of the causative factors in ageing, the selection mechanism for mature mRNA at the level of nuclear matrix attachment is disturbed. In the presence of a superoxide radical-generating system (xanthine/xanthine oxidase), both the mature ovalbumin mRNA and the immature ovalbumin mRNA precursors were found to be released from the nuclear matrix of hen oviduct cells, in the absence as well as in the presence of ATP. This result was also obtained when whole, isolated nuclei preincubated with xanthine/xanthine oxidase were used. The superoxide radical-caused effect could be partially prevented by co-addition of superoxide dismutase (SOD) which dismutates O2- to H2O2 and O2. On the other hand, in the presence of antibodies against the SOD, the effect of superoxide anions on RNA-matrix attachment was enhanced and its inhibition by SOD was abolished. Our results suggest that cellular ageing may be partially caused by superoxide radical-induced release of immature mRNA from its intranuclear binding site resulting in the appearance of immature messengers in the cytoplasm. This may cause both qualitative and quantitative changes in protein synthesis. Thus, ageing may be associated not only with the expression of genes coding for proteins not characteristic for the proper state of differentiation of a given cell (as suggested by the dysdifferentiative hypothesis of ageing) but also with impaired maturation of the primary gene transcripts due to the interference of superoxide radicals, not sufficiently eliminated by antioxidant mechanisms with age, with RNA-matrix attachment.
在真核细胞中，未成熟的mRNA通常局限于细胞核内，在那里它经过转录后加工成为成熟的mRNA。未成熟和成熟mRNA的核内结合位点被认为是核基质，它作为转录后RNA成熟和运输的平台。成熟mRNA物种核质运输的选择性似乎是由于ATP导致成熟mRNA从核基质释放的选择性；在这种核苷酸存在的情况下，未成熟mRNA与基质的附着不会改变。在这里，我们表明，在超氧阴离子（O2-）存在的情况下，超氧阴离子很可能是衰老的致病因素之一，在核基质附着水平上成熟mRNA的选择机制受到干扰。在超氧阴离子生成系统（黄嘌呤/黄嘌呤氧化酶）存在的情况下，无论是在有无ATP的情况下，成熟的卵清蛋白mRNA和未成熟的卵清蛋白mRNA前体都从母鸡输卵管细胞的核基质中释放出来。当使用预先与黄嘌呤/黄嘌呤氧化酶孵育的完整分离细胞核时，也得到了这一结果。超氧阴离子引起的效应可以通过共添加超氧化物歧化酶（SOD）来部分预防，SOD将O2-歧化为H2O2和O2。另一方面，在存在抗SOD抗体的情况下，超氧阴离子对RNA-基质附着的影响增强，并且其被SOD的抑制作用被消除。我们的结果表明，细胞衰老可能部分是由于超氧阴离子诱导未成熟mRNA从其核内结合位点释放，导致未成熟信使出现在细胞质中。这可能会导致蛋白质合成在质量和数量上的变化。因此，衰老不仅可能与编码给定细胞正常分化状态不典型蛋白质的基因表达有关（如衰老的分化异常假说所暗示的），还可能与由于超氧阴离子的干扰导致的初级基因转录本成熟受损有关，随着年龄的增长，抗氧化机制不能充分消除超氧阴离子，超氧阴离子会干扰RNA-基质的附着。
