A Mechanosensor Mechanism Controls the G-Quadruplex/i-Motif Molecular Switch in the MYC Promoter NHE III1
A Mechanosensor Mechanism Controls the G-Quadruplex/i-Motif Molecular Switch in the MYC Promoter NHE III1
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DOI：
10.1021/jacs.6b09196
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发表时间：
2016-10-26
影响因子：
15
通讯作者：
Hurley, Laurence H.
中科院分区：
文献类型：
--
作者：
Sutherland, Caleb;Cui, Yunxi;Hurley, Laurence H.
MYC在许多不同的癌症类型中过表达，并且由于其对肿瘤发生的贡献而成为深入研究的癌基因。MYC的调控是复杂的，NHE III 1和FUSE元件依赖于非经典的DNA结构和转录诱导的负超螺旋。在NHE III 1中，只有G-四链体被广泛研究，而在相反的富含C链上形成的i-基序的作用则知之甚少。我们在这里证明，i-基序是在4CT元件内形成的，并被hnRNP K识别，这导致低水平的转录激活。对于最大的hnRNP K转录激活，两个额外的胞嘧啶运行，位于下游的i-基序形成区域的7个碱基，也是必需的。为了获得这些额外的胞嘧啶运行，增加负超螺旋是必要的，这导致hnRNP K和未折叠的i-基序之间的化学稳定的复合物。我们还证明了MYC G-四链体和i-基序之间的互斥性，为SP1诱导的负超螺旋驱动的分子开关机制提供了理论基础，其中相对hnRNP K和核仁素表达将平衡转移到开或关状态。
MYC is overexpressed in many different cancer types and is an intensively studied oncogene because of its contributions to tumorigenesis. The regulation of MYC is complex, and the NHE III1 and FUSE elements rely upon noncanonical DNA structures and transcriptionally induced negative superhelicity. In the NHE III1 only the G-quadruplex has been extensively studied, whereas the role of the i-motif, formed on the opposite C-rich strand, is much less understood. We demonstrate here that the i-motif is formed within the 4CT element and is recognized by hnRNP K, which leads to a low level of transcription activation. For maximal hnRNP K transcription activation, two additional cytosine runs, located seven bases downstream of the i-motif-forming region, are also required. To access these additional runs of cytosine, increased negative superhelicity is necessary, which leads to a thermodynamically stable complex between hnRNP K and the unfolded i-motif. We also demonstrate mutual exclusivity between the MYC G-quadruplex and i-motif, providing a rationale for a molecular switch mechanism driven by SP1-induced negative superhelicity, where relative hnRNP K and nucleolin expression shifts the equilibrium to the on or off state.