Quadruplex formation by both G-rich and C-rich DNA strands of the C9orf72 (GGGGCC)8•(GGCCCC)8 repeat: effect of CpG methylation.
Quadruplex formation by both G-rich and C-rich DNA strands of the C9orf72 (GGGGCC)8•(GGCCCC)8 repeat: effect of CpG methylation.
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DOI：
10.1093/nar/gkv1008
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发表时间：
2015-11-16
影响因子：
14.9
通讯作者：
Pearson CE
中科院分区：
文献类型：
--
作者：
Zamiri B;Mirceta M;Bomsztyk K;Macgregor RB Jr;Pearson CE
C9orf72重复序列的异常DNA/RNA结构可能参与肌萎缩侧索硬化症和额颞叶痴呆的重复扩增或发病机制。扩增重复序列被CpG甲基化，后果未知。通常，四重结构是由富g链而不是互补的富c链形成的。利用CD、UV和电泳对（GGGGCC）8和（GGCCCC）8链在5-甲基胞嘧啶（5mCpG）或5-羟甲基胞嘧啶（5hmCpG）甲基化和未甲基化时形成的结构进行了表征。所有链都形成了异质的结构混合物，具有四重结构的特征（在pH 7.5下，在K+， Na+或Li+中），但没有典型的i基序特征。富含C的链形成四联体，可能被G•C•G•C-四联体和C•C•C•C-四联体稳定。与G•G•G•G四元构象不同，一些G•C•G•C四元构象不需要n7 -鸟嘌呤的位置，因此当n7 -去氮鸟嘌呤取代所有鸟嘌呤时仍然形成C9orf72四元构象。5mCpG和5hmCpG增加和降低了这些结构的热稳定性。通过带移分析，hnRNPK结合了富含c而不是富含g的链，结合偏好为未甲基化的> 5hmCpG > 5mCpG，其中甲基化的dna -蛋白复合物保留在孔中，与未甲基化的复合物不同。我们的研究结果表明，对于点缀着g残基的富c序列，必须考虑四重体的形成，四重体的甲基化可能影响表观遗传过程。
Unusual DNA/RNA structures of the C9orf72 repeat may participate in repeat expansions or pathogenesis of amyotrophic lateral sclerosis and frontotemporal dementia. Expanded repeats are CpG methylated with unknown consequences. Typically, quadruplex structures form by G-rich but not complementary C-rich strands. Using CD, UV and electrophoresis, we characterized the structures formed by (GGGGCC)8 and (GGCCCC)8 strands with and without 5-methylcytosine (5mCpG) or 5-hydroxymethylcytosine (5hmCpG) methylation. All strands formed heterogenous mixtures of structures, with features of quadruplexes (at pH 7.5, in K+, Na+ or Li+), but no feature typical of i-motifs. C-rich strands formed quadruplexes, likely stabilized by G•C•G•C-tetrads and C•C•C•C-tetrads. Unlike G•G•G•G-tetrads, some G•C•G•C-tetrad conformations do not require the N7-Guanine position, hence C9orf72 quadruplexes still formed when N7-deazaGuanine replace all Guanines. 5mCpG and 5hmCpG increased and decreased the thermal stability of these structures. hnRNPK, through band-shift analysis, bound C-rich but not G-rich strands, with a binding preference of unmethylated > 5hmCpG > 5mCpG, where methylated DNA-protein complexes were retained in the wells, distinct from unmethylated complexes. Our findings suggest that for C-rich sequences interspersed with G-residues, one must consider quadruplex formation and that methylation of quadruplexes may affect epigenetic processes.