EGFR inhibits DNA mismatch repair.
EGFR inhibits DNA mismatch repair.
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EGFR 抑制 DNA 错配修复。
DOI：
10.1073/pnas.1505168112
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发表时间：
2015
影响因子：
11.1
通讯作者：
Pearlman,AlexanderH
中科院分区：
文献类型：
--
作者：
Hsieh,Peggy;Pearlman,AlexanderH
保护基因组的完整性不应心存侥幸。事实上，所有生物体都有高效的机制来检测和消除 DNA 中的错误和损伤。 DNA错配修复（MMR）是确保从细菌到人类的DNA复制保真度的最终保障，并支持复制聚合酶的核苷酸选择和核酸外切酶校对活动（图1）（1-3）。 MMR 的缺失导致自发突变率大大升高，是林奇综合征结肠癌的根本原因，并且与散发性肿瘤的子集有关。在其复制后能力中，MMR 在 S 期发挥作用，与复制叉密切相关。该过程由增殖细胞核抗原蛋白 (PCNA) 介导，PCNA 是调节 DNA 聚合酶和参与复制、修复和重组的其他蛋白质的进入和活性的关键 (4)。 EGFR 是跨越质膜的受体酪氨酸激酶 (RTK) HER 家族的成员，可响应细胞外配体（例如 EGF）调节细胞增殖、分化和运动(5, 6)。配体结合促进细胞质激酶结构域的二聚化和变构激活。自磷酸化启动涉及 RAS/MAPK、PI (3) K/Akt、Jak/STAT 等的信号级联。 EGFR 还会易位到细胞核，影响复制、修复和转录，并与多种恶性肿瘤的不良预后相关，但分子机制很大程度上未知 (7, 8)。在细胞核中，EGFR 使 PCNA 磷酸化，从而提高其稳定性 (9)。预计这会产生重要的后果，但迄今为止其功能意义尚不清楚。在 PNAS 中，奥尔特加等人。揭示 EGFR 对 PCNA 的磷酸化会抑制细胞中的 MMR，并将体外 DNA 合成从高保真度转变为容易出错的状态（图 2）(10)。 MMR 和 EGFR 之间的这种交叉强调了了解 EGFR 和其他 RTK 的核作用的重要性，并强调了细胞增殖的控制和基因组稳定性的维持（肿瘤发生的两个核心方面）之间的关系。尽管复制非常忠实，但复制聚合酶大约每 104 至 105 次掺入一个不正确的核苷酸，导致产生诱变前的非沃森-克里克碱基对，例如 G: T。此外，在通过单核苷酸和二核苷酸重复进行复制的过程中，模板链可能会错位，形成插入/删除环（IDL），从而产生插入或删除突变。细胞如何减少复制错误？校对核酸外切酶活性是复制聚合酶不可或缺的组成部分，可以去除错误掺入的核苷酸，但它并不是铁定的。问题更大的是 IDL 很可能完全逃脱校对。 MMR 充当最后的看门人，切除新子链中的错误，并在间隙填充步骤中为复制聚合酶提供第二次机会。突变或表观遗传沉默导致 MMR 丧失，使自发突变增加 50 至 1,000 倍，是林奇综合征结肠癌和散发性癌症亚型的恶性肿瘤的驱动因素 (11, 12)。 PCNA 是聚合酶的持续合成因子，可能在错配识别、新合成链切除以及复制聚合酶 DNA 合成等 MMR 中发挥作用 (1, 3)。在真核生物中，错配修复是由与细菌 MutS 相关的保守错配结合蛋白启动的：MutSα（MSH2-MSH6 的异二聚体）和 MutSβ（MSH2-MSH3 的异二聚体）。 MutSα 针对碱基错配和 1-2 个核苷酸的 IDL，而 MutSβ 优先针对 IDL……
Safeguarding the integrity of the genome should not be left to chance. Indeed, all organisms have highly effective mechanisms to detect and remove errors and lesions in DNA. DNA mismatch repair (MMR) serves as the final safeguard in assuring the fidelity of DNA replication from bacteria to humans and backstops the nucleotide selection and exonuclease proofreading activities of replicative polymerases (Fig. 1)(1–3). The loss of MMR results in greatly elevated rates of spontaneous mutation, is the underlying cause of Lynch syndrome colon cancer, and is implicated in a subset of sporadic tumors. In its postreplication capacity, MMR functions during S phase in close association with the replication fork. This process is mediated by proliferating cell nuclear antigen protein (PCNA), a lynchpin in regulating access and activity of DNA polymerases and other proteins involved in replication, repair, and recombination (4). EGFR, a member of the HER family of receptor tyrosine kinases (RTKs) that span the plasma membrane, regulates cell proliferation, differentiation, and motility in response to extracellular ligands (eg, EGF)(5, 6). Ligand binding promotes dimerization and allosteric activation of cytoplasmic kinase domains. Autophosphorylation initiates signaling cascades involving RAS/MAPK, PI (3) K/Akt, Jak/STAT, and others. EGFR also translocates to the nucleus where it influences replication, repair, and transcription and is linked to poor prognoses in several malignancies, but molecular mechanisms are largely unknown (7, 8). In the nucleus, EGFR phosphorylates PCNA, increasing its stability (9). This would be expected to have important consequences, but the functional significance was unclear until now. In PNAS, Ortega et al. reveal that phosphorylation of PCNA by EGFR inhibits MMR in cells and switches DNA synthesis in vitro from highfidelity to error-prone (Fig. 2)(10). This intersection between MMR and EGFR underscores the importance of understanding the nuclear roles of EGFR and other RTKs, and highlights the relationship between the control of cell proliferation and the maintenance of genome stability, two central aspects of tumorigenesis. Although replication is remarkably faithful, replicative polymerases incorporate an incorrect nucleotide leading to premutagenic, non-Watson–Crick base pairs, such as G: T, about once every 104 to 105 times. In addition, during replication through mono-and dinucleotide repeats, the template strand can misalign, forming insertion/deletion loops (IDLs) that yield insertion or deletion mutations. How do cells mitigate replication errors? A proofreading exonuclease activity that is an integral component of replicative polymerases removes misincorporated nucleotides, but it’s not ironclad. More problematic are IDLs that are likely to escape proofreading altogether. MMR serves as the final gatekeeper, excising errors in new daughter strands and giving replicative polymerases a second chance in a gap-filling step. The loss of MMR by mutation or epigenetic silencing increases spontaneous mutation by 50-to 1,000-fold and is a driver of malignancy in Lynch syndrome colon cancer and a subset of sporadic cancers (11, 12). PCNA is a processivity factor for polymerases and likely functions in MMR at mismatch recognition, excision on the newly synthesized strand, and DNA synthesis by replicative polymerases (1, 3). In eukaryotes, mismatch repair is initiated by conserved mismatch binding proteins related to bacterial MutS: MutSα, a heterodimer of MSH2-MSH6, and MutSβ, a heterodimer of MSH2-MSH3. MutSα targets base-base mispairs andIDLs of 1–2 nucleotides, whereas MutSβ preferentially targets IDLs …