Grand Cory L, Powell Tiffanie J, Nagle Raymond B, Bearss David J, Tye Denise, Gleason-Guzman Mary, Hurley Laurence H
Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, AZ 85724, USA.
Proc Natl Acad Sci U S A. 2004 Apr 20;101(16):6140-5. doi: 10.1073/pnas.0400460101. Epub 2004 Apr 12.
We have demonstrated that a parallel G-quadruplex structure in the c-MYC promoter functions as a transcriptional repressor element. Furthermore, a specific G-to-A mutation in this element results in destabilization of the G-quadruplex repressor element and an increase in basal transcriptional activity. To validate this model in an in vivo context, we have examined the sequence of this region in human colorectal tumors and the surrounding normal tissue. We have found that approximately 30% of tumors contain one of two specific G-to-A mutations, not present in the surrounding normal tissue, that destabilize the parallel G-quadruplex, which would be expected to give rise to abnormally high expression of c-MYC in these cells. In contrast, G-quadruplex-disruptive mutations were absent in 20 colon adenomas, suggesting that these mutations occur late in tumorigenesis. We have also demonstrated that these same mutations are found in established colorectal cell lines. NM23-H2 levels are lower in cancer tissues and cell lines that harbor these mutations. In cells with repressed levels of NM23-H2, the mutated and destabilized G-quadruplex silencer element can be reinstated by the addition of G-quadruplex-stabilizing compounds, providing an opportunity for therapeutic intervention for patients carrying these mutations.
我们已经证明，c-MYC启动子中的平行G-四链体结构作为转录抑制元件发挥作用。此外，该元件中特定的G到A突变导致G-四链体抑制元件不稳定，并增加基础转录活性。为了在体内验证该模型，我们检查了人类结直肠癌肿瘤及周围正常组织中该区域的序列。我们发现，约30%的肿瘤含有两种特定的G到A突变之一，而周围正常组织中不存在这些突变，这些突变会使平行G-四链体不稳定，预计会导致这些细胞中c-MYC异常高表达。相比之下，20例结肠腺瘤中不存在破坏G-四链体的突变，这表明这些突变发生在肿瘤发生的晚期。我们还证明，在已建立的结直肠癌细胞系中也发现了相同的突变。在含有这些突变的癌症组织和细胞系中，NM23-H2水平较低。在NM23-H2水平受到抑制的细胞中，添加G-四链体稳定化合物可恢复突变且不稳定的G-四链体沉默元件，为携带这些突变的患者提供了治疗干预的机会。
