Key Laboratory of Molecular Epigenetics of Ministry of Education, Institute of Cytology and Genetics, Northeast Normal University, Changchun, China.
PLoS One. 2012;7(5):e38074. doi: 10.1371/journal.pone.0038074. Epub 2012 May 29.
Dependence receptors have been proved to act as tumor suppressors in tumorigenesis. Neogenin, a DCC homologue, well known for its fundamental role in axon guidance and cellular differentiation, is also a dependence receptor functioning to control apoptosis. However, loss of neogenin has been reported in several kinds of cancers, but its role in glioma remains to be further investigated.
METHODOLOGY/PRINCIPAL FINDINGS: Western blot analysis showed that neogenin level was lower in glioma tissues than in their matching surrounding non-neoplastic tissues (n = 13, p<0.01). By immunohistochemical analysis of 69 primary and 16 paired initial and recurrent glioma sections, we found that the loss of neogenin did not only correlate negatively with glioma malignancy (n = 69, p<0.01), but also glioma recurrence (n = 16, p<0.05). Kaplan-Meier plot and Cox proportional hazards modelling showed that over-expressive neogenin could prolong the tumor latency (n = 69, p<0.001, 1187.6 ± 162.6 days versus 687.4 ± 254.2 days) and restrain high-grade glioma development (n = 69, p<0.01, HR: 0.264, 95% CI: 0.102 to 0.687). By Methylation specific polymerase chain reaction (MSP), we reported that neogenin promoter was methylated in 31.0% (9/29) gliomas, but absent in 3 kinds of glioma cell lines. Interestingly, the prevalence of methylation in high-grade gliomas was higher than low-grade gliomas and non-neoplastic brain tissues (n = 33, p<0.05) and overall methylation rate increased as glioma malignancy advanced. Furthermore, when cells were over-expressed by neogenin, the apoptotic rate in SHG-44 was increased to 39.7% compared with 8.1% in the blank control (p<0.01) and 9.3% in the negative control (p<0.01).
CONCLUSIONS/SIGNIFICANCE: These observations recapitulated the proposed role of neogenin as a tumor suppressor in gliomas and we suggest its down-regulation owing to promoter methylation is a selective advantage for glioma genesis, progression and recurrence. Furthermore, the induction of apoptosis in SHG-44 cells after overexpression of neogenin, indicated that neogenin could be a novel target for glioma therapy.
依赖性受体已被证明在肿瘤发生中起肿瘤抑制作用。Neogenin 是 DCC 的同源物，因其在轴突导向和细胞分化中的基本作用而闻名，也是一种控制细胞凋亡的依赖性受体。然而，已经报道 Neogenin 在几种癌症中丢失，但它在神经胶质瘤中的作用仍有待进一步研究。
方法/主要发现：Western blot 分析显示，神经胶质瘤组织中的 Neogenin 水平低于其配对的非肿瘤周围组织（n=13，p<0.01）。通过对 69 例原发性和 16 对初始和复发性神经胶质瘤切片的免疫组织化学分析，我们发现 Neogenin 的缺失不仅与神经胶质瘤的恶性程度呈负相关（n=69，p<0.01），而且与神经胶质瘤的复发也呈负相关（n=16，p<0.05）。Kaplan-Meier 图和 Cox 比例风险模型显示，过表达 Neogenin 可以延长肿瘤潜伏期（n=69，p<0.001，1187.6±162.6 天 vs. 687.4±254.2 天）和抑制高级别神经胶质瘤的发展（n=69，p<0.01，HR：0.264，95%CI：0.102-0.687）。通过甲基化特异性聚合酶链反应（MSP），我们报告说，Neogenin 启动子在 31.0%（9/29）的神经胶质瘤中被甲基化，但在 3 种神经胶质瘤细胞系中不存在。有趣的是，高级别神经胶质瘤中的甲基化发生率高于低级别神经胶质瘤和非肿瘤性脑组织（n=33，p<0.05），并且随着神经胶质瘤恶性程度的升高，总体甲基化率增加。此外，当细胞通过 Neogenin 过表达时，SHG-44 中的细胞凋亡率增加到 39.7%，而空白对照组为 8.1%（p<0.01），阴性对照组为 9.3%（p<0.01）。
结论/意义：这些观察结果再现了 Neogenin 作为神经胶质瘤肿瘤抑制因子的作用，我们认为其启动子甲基化导致的下调是神经胶质瘤发生、进展和复发的选择性优势。此外，过表达 Neogenin 后 SHG-44 细胞的凋亡诱导表明 Neogenin 可能成为神经胶质瘤治疗的新靶点。
