Qiao F, Moss A, Kupfer G M
Departments of Microbiology and Pediatrics, University of Virginia and the University of Virginia Health System, Charlottesville, Virginia 22908, USA.
J Biol Chem. 2001 Jun 29;276(26):23391-6. doi: 10.1074/jbc.M101855200. Epub 2001 Apr 10.
Fanconi anemia (FA) is a genetic disease characterized by congenital defects, bone marrow failure, and cancer susceptibility. Cells from patients with FA exhibit genomic instability and hypersensitivity to DNA cross linking agents such as mitomycin C. Despite the identification of seven complementation groups and the cloning of six genes, the function of the encoded gene products remains elusive. The FancA (Fanconi anemia complementation group A), FancC, and FancG proteins have been detected within a nuclear complex, but no change in level, binding, or localization has been reported as a result of drug treatment or cell cycle. We show that in immunofluorescence studies, FancA appears as a non-nucleolar nuclear protein that is excluded from condensed, mitotic chromosomes. Biochemical fractionation reveals that the FA proteins are found in nuclear matrix and chromatin and that treatment with mitomycin C results in increase of the FA proteins in nuclear matrix and chromatin fractions. This induction occurs in wild-type cells and mutant FA-D (Fanconi complementation group D) cells but not in mutant FA-A cells. Immunoprecipitation of FancA protein in chromatin demonstrates the coprecipitation of FancA, FancC, and FancG, showing that the FA proteins move together as a complex. Also, fractionation of mitotic cells confirms the lack of FA proteins in chromatin or the nuclear matrix. Furthermore, phosphorylation of FancG was found to be temporally correlated with exit of the FA complex from chromosomes at mitosis. Taken together, these findings suggest a role for FA proteins in chromatin and nuclear matrix.
范可尼贫血（FA）是一种遗传性疾病，其特征为先天性缺陷、骨髓衰竭和癌症易感性。FA患者的细胞表现出基因组不稳定以及对丝裂霉素C等DNA交联剂高度敏感。尽管已鉴定出七个互补组并克隆了六个基因，但编码基因产物的功能仍不清楚。FancA（范可尼贫血互补组A）、FancC和FancG蛋白已在一个核复合物中被检测到，但未报道药物处理或细胞周期导致其水平、结合或定位发生变化。我们发现在免疫荧光研究中，FancA表现为一种非核仁核蛋白，被排除在浓缩的有丝分裂染色体之外。生化分级分离显示，FA蛋白存在于核基质和染色质中，用丝裂霉素C处理会导致核基质和染色质组分中FA蛋白增加。这种诱导在野生型细胞和突变型FA-D（范可尼互补组D）细胞中发生，但在突变型FA-A细胞中不发生。对染色质中FancA蛋白进行免疫沉淀显示FancA、FancC和FancG共沉淀，表明FA蛋白作为一个复合物一起移动。此外，有丝分裂细胞的分级分离证实染色质或核基质中缺乏FA蛋白。此外，发现FancG的磷酸化与有丝分裂时FA复合物从染色体上脱离在时间上相关。综上所述，这些发现表明FA蛋白在染色质和核基质中发挥作用。
