Cheng Wen-Hsing, Sakamoto Shuichi, Fox Jennifer T, Komatsu Kenshi, Carney James, Bohr Vilhelm A
Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
FEBS Lett. 2005 Feb 28;579(6):1350-6. doi: 10.1016/j.febslet.2005.01.028. Epub 2005 Jan 28.
The WRN protein is mutated in the chromosomally unstable Werner syndrome (WS) and the Nbs1 protein is mutated in Nijmegen breakage syndrome (NBS). The Nbs1 protein is an integral component of the M/R/N complex. Although WRN is known to interact with this complex in response to gamma-irradiation, the mechanism of action is unclear. Here, we show that WRN co-localizes and associates with gamma H2AX, a marker protein of DNA double strand breaks (DSBs), after cellular exposure to gamma-irradiation. While the DNA damage-inducible Nbs1 foci formation is normal in WS cells, WRN focus formation is defective in NBS cells. Consistent with this, gamma H2AX colocalizes with Nbs1 in WS cells but not with WRN in NBS cells. The defective WRN-gamma H2AX association in NBS cells can be complemented with wild-type Nbs1, but not with an Nbs1 S343A point mutant that lacks an ATM phosphorylation site. WRN associates with H2AX in a manner dependent upon the M/R/N complex. Our results suggest a novel pathway in which Nbs1 may recruit WRN to the site of DNA DSBs in an ATM-dependent manner.
WRN蛋白在染色体不稳定的沃纳综合征（WS）中发生突变，而Nbs1蛋白在尼杰梅根断裂综合征（NBS）中发生突变。Nbs1蛋白是M/R/N复合物的一个组成部分。虽然已知WRN在γ射线照射后与该复合物相互作用，但其作用机制尚不清楚。在此，我们表明，细胞暴露于γ射线照射后，WRN与γH2AX共定位并结合，γH2AX是DNA双链断裂（DSB）的标记蛋白。虽然DNA损伤诱导的Nbs1焦点形成在WS细胞中是正常的，但WRN焦点形成在NBS细胞中存在缺陷。与此一致的是，γH2AX在WS细胞中与Nbs1共定位，但在NBS细胞中不与WRN共定位。NBS细胞中WRN与γH2AX的缺陷结合可以用野生型Nbs1来补充，但不能用缺乏ATM磷酸化位点的Nbs1 S343A点突变体来补充。WRN以依赖于M/R/N复合物的方式与H2AX结合。我们的结果提示了一条新的途径，其中Nbs1可能以ATM依赖的方式将WRN募集到DNA DSB位点。
