The Function of Werner Syndrome Protein

Werner综合征（WS）是一种纯合子隐性疾病，其特征在于早期发作的许多正常衰老特征，如皮肤变白、头发变灰、白内障、糖尿病和骨质疏松症。由于WS的衰老加速，对这种疾病的研究将有望揭示正常衰老中发生的退行性过程。来自WS患者的细胞比年龄匹配的正常细胞生长得更慢，并且在更早的群体倍增时衰老，这可能是因为这些细胞似乎以加速的速度失去了染色体的端粒末端。一般来说，WS细胞具有高水平的基因组不稳定性，DNA缺失、插入和重排的量增加。这些影响可能是DNA修复、复制和/或重组缺陷的结果，尽管实际的生化缺陷仍然未知。WS中有缺陷的基因WRN基因已被鉴定和表征。我们已经制备了纯化的WRN蛋白，用于许多基本和复杂的生化测定。我们正在寻求几种途径来识别和表征WS细胞中的生化缺陷。WRN蛋白具有解旋酶活性，并且将解旋小的和大的DNA双链体构建体。它还将解开不寻常的DNA结构，如三螺旋和DNA叉。我们将Werner解旋酶活性与RecQ解旋酶家族中的另一种解旋酶活性进行比较，RecQ解旋酶家族都参与基因组稳定性的维持。WRNp具有另一种酶活性，即3-5'核酸外切酶功能。我们正在寻找WRN参与的途径，并发现了许多新的功能和物理蛋白质与Werner蛋白的相互作用。 我们的数据有力地表明，WRN参与了两个主要的DNA修复途径：碱基切除修复和重组。 这一结论得到了蛋白质功能相互作用的生物化学研究和细胞生物学数据的支持。 此外，我们的观察和其他工作的结果表明，WRN的主要功能是在端粒末端。 WRN与关键的端粒蛋白如TRF 1和2以及POT 1相互作用。 这些功能性蛋白质相互作用的观察证实了细胞生物学观察表明，WRN蛋白参与DNA修复过程和端粒末端的维护。WRN也参与DNA修复过程。具体而言，我们发现在体外和体内的证据WRN的氧化DNA碱基损伤的DNA修复和双链断裂的DNA修复中的作用。此外，WRN蛋白的翻译后修饰可以改变其在DNA修复过程中的活性，从而可能参与这些过程的调节。例如，WRN的乙酰化增强了其在DNA修复中的活性，并且可能是DNA损伤信号传导中的重要步骤。我们还表征了在简单生物体线虫中发现的WRNp同源物的功能。 有趣的是，线虫WRN蛋白具有与人类WRNp相似的生化特征。

Werner's syndrome (WS) is a homozygous recessive disease characterized by early onset of many characteristics of normal aging, such as wrinkling of the skin, graying of the hair, cataracts, diabetes, and osteoporosis. Because of the acceleration of aging in WS, the study of this disease will hopefully shed light on the degenerative processes that occur in normal aging. Cells from WS patients grow more slowly and senescence at an earlier population doubling than age-matched normal cells, possibly because these cells appear to lose the telomeric ends of their chromosomes at an accelerated rate. In general, WS cells have a high level of genomic instability, with increased amounts of DNA deletions, insertions, and rearrangements. These effects could potentially be the result of defects in DNA repair, replication, and/or recombination, although the actual biochemical defect remains unknown. The gene that is defective in WS, the WRN gene, has been identified and characterized. We have made purified WRN protein for use in a number of basic and complex biochemical assays. We are pursuing several avenues to identify and characterize the biochemical defect in WS cells. WRN protein has helicase activity and will unwind small and large DNA duplex constructs. It will also unwind unusual DNA structures such as triple helices and DNA forks. We are comparing the Werner helicase activity to that of another helicases in the family of RecQ helicases that are all involved in the maintenace of genome stability. WRNp has another enzymatic activity, a 3-5' exonuclease function. We are searching for pathways in which WRN participates and have discovered a number of new functional and physical protein interactions with Werner protein. Our data strongly suggest that WRN is involved in two of the major DNA repair pathways: base excision repair and recombination. This conclusion is supported by biochemical studies of protein functional interaction and by cell biological data. Further, our observations and results from other work suggest that a major function of WRN is at the telomere end. WRN interacts with key telomeric proteins such as TRF1 and 2 and POT1. These observations of functional protein interactions corroborated by cell biological observations suggest that WRN protein is involved in DNA repair processes and maintenance at the telomere end. WRN is also involved in the DNA repair process. Specifically, we find in vitro and in vivo evidence for a role of WRN in the DNA repair of oxidative DNA base lesions and in the DNA repair of double strand breaks. Further, post-translational modification of WRN protein can changes its activities in the DNA repair process and thus might be involved in the regulation of these processes. For example, the acetylation of WRN enhances its activities in DNA repair and is likely a significant step in DNA damage signaling. We have also characterized the function of the homolog of WRNp found in the simple organism, the nematode. Interestingly, the nematode WRN protein has similar biochemical characteristics to the human WRNp.