Zhitkovich A, Voitkun V, Costa M
Nelson Institute of Environmental Medicine, New York University Medical Center, NY 10016, USA.
Carcinogenesis. 1995 Apr;16(4):907-13. doi: 10.1093/carcin/16.4.907.
Exposure of cells to carcinogenic Cr(VI) compounds results in the formation of several types of DNA lesions such as strand breaks, DNA-protein crosslinks and uncharacterized DNA-Cr adducts. Hexavalent chromium compounds are positive in most bacterial and eukaryotic mutagenic systems, although the nature of DNA modifications underlying the chromium-induced mutagenesis is not known. Hexavalent chromate(VI) is very active in cellular systems because it is actively transported into cells, but intracellularly it is ultimately reduced to Cr(III). Here we show that exposure of Chinese hamster ovary (CHO) cells to potassium chromate(VI) leads to the formation of stable complexes between DNA and amino acids or glutathione. Cysteine, glutamic acid and histidine were the major amino acids crosslinked to DNA in chromate-treated cells. Incubation of purified DNA in the presence of EDTA dissociated SDS stable amino acid-DNA complexes, which indicates that these DNA adducts are most likely to represent ternary coordination complexes mediated by Cr(III) rather than covalent linkage between amino acids/glutathione and DNA. The amino acids that were found complexed with DNA purified from chromate-exposed cells did not orginate from previously crosslinked proteins during DNA isolation, but represented authentic reactions of free amino acids and glutathione with chromium and DNA in cells. Ternary complexes of glutathione or amino acids with Cr(III) and DNA were estimated to account for as much as 50% of DNA-bound chromium following exposure to < or = 25 microM chromate.
细胞暴露于致癌性六价铬化合物会导致形成多种类型的DNA损伤，如链断裂、DNA-蛋白质交联以及未明确特征的DNA-铬加合物。六价铬化合物在大多数细菌和真核生物诱变系统中呈阳性，尽管铬诱导诱变作用背后的DNA修饰本质尚不清楚。六价铬酸盐（VI）在细胞系统中非常活跃，因为它能被主动转运到细胞内，但在细胞内最终会被还原为三价铬（III）。在此我们表明，中国仓鼠卵巢（CHO）细胞暴露于铬酸钾（VI）会导致DNA与氨基酸或谷胱甘肽之间形成稳定复合物。半胱氨酸、谷氨酸和组氨酸是铬酸盐处理细胞中与DNA交联的主要氨基酸。在EDTA存在下孵育纯化的DNA会使SDS稳定的氨基酸-DNA复合物解离，这表明这些DNA加合物很可能代表由三价铬（III）介导的三元配位复合物，而非氨基酸/谷胱甘肽与DNA之间的共价连接。从铬酸盐暴露细胞中纯化出的与DNA复合的氨基酸并非来自DNA分离过程中先前交联的蛋白质，而是代表细胞中游离氨基酸和谷胱甘肽与铬和DNA的真实反应。在暴露于≤25微摩尔铬酸盐后，谷胱甘肽或氨基酸与三价铬（III）和DNA的三元复合物估计占结合到DNA上的铬的50%之多。
