Institut de Recherche en Cancérologie de Montpellier (INSERM-Université de Montpellier I U896), CRLC Val d'Aurelle-Paul Lamarque, 34298 Montpellier-Cedex 5, France.
Biochem Biophys Res Commun. 2010 Feb 5;392(2):129-34. doi: 10.1016/j.bbrc.2009.12.159. Epub 2010 Jan 4.
The INK4B-ARF-INK4A (INK/ARF) locus is composed of three tumor suppressor genes, which are kept silenced by DNA methylation in different cancer types. In addition, a non-coding RNA (ANRIL) is transcribed in the anti-sense orientation upstream of the ARF gene. The resulting divergent promoter region is bound by the chromatin insulator protein CTCF in association with histone H3 tri-methylated on lysine 4, irrespective of transcription of ANRIL and ARF. Methylation of the overlapping CpG island abolishes CTCF binding and the associated modification, which can be restored by 5-Aza-2'-deoxycytidine (5-Aza-dC) treatment. shRNA knock down of CTCF expression dramatically reduces the induction of ANRIL and ARF, but also that of INK4A and INK4B expression by 5-Aza-dC. We propose that CTCF is an essential factor for transcription of the INK/ARF locus and that abrogation of its binding by DNA methylation contributes to the permanent silencing of several genes of the locus in tumors.
INK4B-ARF-INK4A（INK/ARF）基因座由三个肿瘤抑制基因组成，在不同的癌症类型中，这些基因通过 DNA 甲基化而保持沉默。此外，在 ARF 基因的上游反义方向转录一种非编码 RNA（ANRIL）。由此产生的发散启动子区域由染色质绝缘子蛋白 CTCF 与组蛋白 H3 赖氨酸 4 上的三甲基化结合，而与 ANRIL 和 ARF 的转录无关。重叠的 CpG 岛的甲基化会破坏 CTCF 结合及其相关修饰，5-Aza-2'-脱氧胞苷（5-Aza-dC）处理可以恢复这种结合及其相关修饰。shRNA 敲低 CTCF 表达会显著降低 5-Aza-dC 诱导的 ANRIL 和 ARF 的表达，也会降低 INK4A 和 INK4B 的表达。我们提出 CTCF 是 INK/ARF 基因座转录的必需因子，其通过 DNA 甲基化而结合的缺失导致该基因座的几个基因在肿瘤中永久沉默。
