Galvan L, Evans J E, Huang C H, Prestayko A, Wu B, Crooke S T
Cancer Res. 1982 Apr;42(4):1555-61.
A unique DNA-binding protein was detected that inhibited DNA degradation induced by bleomycin and was decreased in sera of cancer patients. The protein from normal human serum was purified to homogeneity by ammonium sulfate precipitation and DEAE-cellulose and DNA-cellulose column chromatography. Two-dimensional isoelectric focusing gel electrophoresis revealed a single protein spot with a molecular weight of 64,000 and a pI at pH 5.9. The NH2 terminus was lysine, and the ratio of acidic to basic residues was 1.2. DNA binding was demonstrated by column chromatography, agarose gel electrophoresis, fluorescence quenching, and circular dichroism. The inhibitory activity was abolished by treatment with Pronase but not by RNase or DNase I. FeCl2 caused a partial loss of inhibitory activity. The inhibition of DNA degradation was more effective for breakage induced by bleomycin than neocarzinostatin, macromomycin, or DNase I. Evidence from DNA-binding studies suggests the inhibition is due to binding of the protein to sites on DNA preferred by bleomycin. Thus, the protein could be useful for studies on the mechanism of action of bleomycin and other antitumor agents, the cytotoxic effects of which are due primarily to damage of cellular DNA. The protein was decreased significantly in sera of cancer patients, and its potential use as a diagnostic tool for neoplasias is being investigated further.
检测到一种独特的DNA结合蛋白，它能抑制博来霉素诱导的DNA降解，且在癌症患者血清中含量降低。通过硫酸铵沉淀、DEAE - 纤维素和DNA - 纤维素柱色谱法，将正常人血清中的该蛋白纯化至同质。二维等电聚焦凝胶电泳显示有一个单一蛋白斑点，分子量为64,000，pI为pH 5.9。其NH2末端为赖氨酸，酸性与碱性残基的比例为1.2。通过柱色谱法、琼脂糖凝胶电泳、荧光猝灭和圆二色性证明了DNA结合。用链霉蛋白酶处理可消除抑制活性，但用核糖核酸酶或脱氧核糖核酸酶I处理则不能。FeCl2导致抑制活性部分丧失。该蛋白对博来霉素诱导的DNA断裂的抑制作用比对新制癌菌素、巨霉素或脱氧核糖核酸酶I更有效。DNA结合研究的证据表明，这种抑制作用是由于该蛋白与博来霉素优先结合的DNA位点结合所致。因此，该蛋白可用于研究博来霉素和其他抗肿瘤药物的作用机制，这些药物的细胞毒性作用主要是由于细胞DNA损伤。该蛋白在癌症患者血清中显著降低，目前正在进一步研究其作为肿瘤诊断工具的潜在用途。
