INSERM U892, Equipe Apoptose et progression tumorale, Equipe labellisée Ligue Nationale Contre le Cancer, Nantes, France.
Epigenetics. 2009 Oct 1;4(7):487-99. doi: 10.4161/epi.4.7.9883. Epub 2009 Oct 21.
Epigenetic gene inactivation in mammalian cells involves many silencing mechanisms. One of these mechanisms is the transcriptional repression by targeted promoter hypermethylation. However, the molecular mechanisms involved in the site-specific DNA (hyper)methylation are not fully elucidate. By using the Dnmt3a/c-myc interaction as an example, we here showed that this interaction promotes the site-specific methylation of CG dinucleotides localized in c-myc boxes of promoter regions of CDKN2a, CCND1 and TIMP2 genes. Indeed, the invalidation of c-myc reveals that c-myc allows the Dnmt3a recruitment on c-myc box of c-myc-regulated genes. Acellular experiments corroborated and complemented these results by revealing that the specificity of consensus sequence for DNA methylation of Dnmt3a is increased in presence of c-myc. Indeed, our work indicates that Dnmt3a and Dnmt3b have consensus sequences to methylate DNA (T/A/C)(A/T)(T/G/A)CG(T/G/C)G(G/C/A) and (A/C)(C/G/A)(A/G)CGT(C/G)(A/G). Thus, the low specificity of these sequences (consensual for 162 and 48 possibilities, respectively) does not support the idea of targeted DNA methylation. By monitoring transcription factor arrays spotted with 103 transcription factors, we next identified 42 transcription factors interacting with Dnmt3a and Dnmt3b (such as CREB and FOS), 27 transcription factors interacting with Dnmt3a (such as AP2alpha and p53), 10 transcription factors interacting with Dnmt3b (such as SP1 and SP4) and 24 transcription factors devoid of direct interaction with Dnm3a and Dnmt3b (such as C/EBPalpha and NFkappaB-p65). Thus, The description of direct interaction between Dnmt3a and/or Dnmt3b and transcription factors provides rational molecular explanation to the mechanisms of targeted DNA (hyper)methylation, and to the mechanisms by which transcription factors repress genes expression.
哺乳动物细胞中的表观遗传基因失活涉及许多沉默机制。其中一种机制是靶向启动子超甲基化的转录抑制。然而，涉及特定于位点的 DNA（超）甲基化的分子机制尚未完全阐明。通过以 Dnmt3a/c-myc 相互作用为例，我们在这里表明，这种相互作用促进了位于 CDKN2a、CCND1 和 TIMP2 基因启动子区域的 c-myc 盒中 CG 二核苷酸的特异性甲基化。事实上，c-myc 的无效性表明，c-myc 允许 Dnmt3a 募集到 c-myc 调节基因的 c-myc 盒上。细胞外实验通过揭示在存在 c-myc 的情况下 Dnmt3a 对 DNA 甲基化的共有序列特异性增加，证实和补充了这些结果。事实上，我们的工作表明，Dnmt3a 和 Dnmt3b 具有甲基化 DNA 的共有序列（T/A/C）（A/T）（T/G/A）CG（T/G/C）G（G/C/A）和（A/C）（C/G/A）（A/G）CGT（C/G）（A/G）。因此，这些序列的低特异性（分别一致 162 和 48 种可能性）不支持靶向 DNA 甲基化的想法。通过监测用 103 种转录因子点样的转录因子阵列，我们接下来鉴定了 42 种与 Dnmt3a 和 Dnmt3b 相互作用的转录因子（如 CREB 和 FOS），27 种与 Dnmt3a 相互作用的转录因子（如 AP2alpha 和 p53），10 种与 Dnmt3b 相互作用的转录因子（如 SP1 和 SP4）和 24 种与 Dnm3a 和 Dnmt3b 没有直接相互作用的转录因子（如 C/EBPalpha 和 NFkappaB-p65）。因此，Dnmt3a 和/或 Dnmt3b 与转录因子之间的直接相互作用的描述为靶向 DNA（超）甲基化的机制以及转录因子抑制基因表达的机制提供了合理的分子解释。
