Center for Biomolecular Sciences, School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
Proc Natl Acad Sci U S A. 2010 Mar 23;107(12):5375-80. doi: 10.1073/pnas.0910015107. Epub 2010 Mar 8.
The DNA damage response activates several pathways that stall the cell cycle and allow DNA repair. These consist of the well-characterized ATR (Ataxia telangiectasia and Rad-3 related)/CHK1 and ATM (Ataxia telangiectasia mutated)/CHK2 pathways in addition to a newly identified ATM/ATR/p38MAPK/MK2 checkpoint. Crucial to maintaining the integrity of the genome is the S-phase checkpoint that functions to prevent DNA replication until damaged DNA is repaired. Inappropriate expression of the proto-oncogene c-Myc is known to cause DNA damage. One mechanism by which c-Myc induces DNA damage is through binding directly to components of the prereplicative complex thereby promoting DNA synthesis, resulting in replication-associated DNA damage and checkpoint activation due to inappropriate origin firing. Here we show that following etoposide-induced DNA damage translation of c-Myc is repressed by miR-34c via a highly conserved target-site within the 3(') UTR. While miR-34c is induced by p53 following DNA damage, we show that in cells lacking p53 this is achieved by an alternative pathway which involves p38 MAPK signalling to MK2. The data presented here suggest that a major physiological target of miR-34c is c-Myc. Inhibition of miR-34c activity prevents S-phase arrest in response to DNA damage leading to increased DNA synthesis, DNA damage, and checkpoint activation in addition to that induced by etoposide alone, which are all reversed by subsequent c-Myc depletion. These data demonstrate that miR-34c is a critical regulator of the c-Myc expression following DNA damage acting downstream of p38 MAPK/MK2 and suggest that miR-34c serves to remove c-Myc to prevent inappropriate replication which may otherwise lead to genomic instability.
DNA 损伤反应激活了几种途径，这些途径使细胞周期停滞并允许 DNA 修复。这些途径除了新发现的 ATM/ATR/p38MAPK/MK2 检查点外，还包括了特征明确的 ATR（共济失调毛细血管扩张症和 Rad-3 相关）/CHK1 和 ATM（共济失调毛细血管扩张症突变）/CHK2 途径。为了维护基因组的完整性，S 期检查点至关重要，它的功能是防止 DNA 复制，直到受损的 DNA 得到修复。众所周知，原癌基因 c-Myc 的异常表达会导致 DNA 损伤。c-Myc 诱导 DNA 损伤的一种机制是通过直接与前复制复合物的成分结合，从而促进 DNA 合成，导致复制相关的 DNA 损伤和由于不合适的起始点引发的检查点激活。在这里，我们发现，在依托泊苷诱导的 DNA 损伤后，c-Myc 的翻译通过 3'UTR 内高度保守的靶位被 miR-34c 抑制。虽然 miR-34c 是在 DNA 损伤后由 p53 诱导的，但我们发现，在缺乏 p53 的细胞中，这是通过涉及 p38MAPK 信号向 MK2 的替代途径实现的。这里呈现的数据表明，miR-34c 的一个主要生理靶标是 c-Myc。抑制 miR-34c 活性可防止 DNA 损伤引起的 S 期停滞，导致 DNA 合成增加、DNA 损伤和检查点激活，这与依托泊苷单独诱导的激活相当，而这些激活都可以被随后的 c-Myc 耗竭所逆转。这些数据表明，miR-34c 是 DNA 损伤后 c-Myc 表达的关键调节因子，它作用于 p38MAPK/MK2 的下游，并表明 miR-34c 用于去除 c-Myc，以防止不适当的复制，否则可能导致基因组不稳定。
