Department of Surgery, Yale Endocrine Neoplasia Laboratory, Yale University School of Medicine, New Haven, CT 06520, USA.
Mol Cancer. 2013 Aug 5;12:87. doi: 10.1186/1476-4598-12-87.
Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with high mutational heterogeneity and a generally poor clinical outcome. Despite implicated roles of deregulated TP53, IGF-2 and Wnt signaling pathways, a clear genetic association or unique mutational link to the disease is still missing. Recent studies suggest a crucial role for epigenetic modifications in the genesis and/or progression of ACC. This study specifically evaluates the potential role of epigenetic silencing of RASSF1A, the most commonly silenced tumor suppressor gene, in adrenocortical malignancy.
Using adrenocortical tumor and normal tissue specimens, we show a significant reduction in expression of RASSF1A mRNA and protein in ACC. Methylation-sensitive and -dependent restriction enzyme based PCR assays revealed significant DNA hypermethylation of the RASSF1A promoter, suggesting an epigenetic mechanism for RASSF1A silencing in ACC. Conversely, the RASSF1A promoter methylation profile in benign adrenocortical adenomas (ACAs) was found to be very similar to that found in normal adrenal cortex. Enforced expression of ectopic RASSF1A in the SW-13 ACC cell line reduced the overall malignant behavior of the cells, which included impairment of invasion through the basement membrane, cell motility, and solitary cell survival and growth. On the other hand, expression of RASSF1A/A133S, a loss-of-function mutant form of RASSF1A, failed to elicit similar malignancy-suppressing responses in ACC cells. Moreover, association of RASSF1A with the cytoskeleton in RASSF1A-expressing ACC cells and normal adrenal cortex suggests a role for RASSF1A in modulating microtubule dynamics in the adrenal cortex, and thereby potentially blocking malignant progression.
Downregulation of RASSF1A via promoter hypermethylation may play a role in the malignant progression of adrenocortical carcinoma possibly by abrogating differentiation-promoting RASSF1A- microtubule interactions.
肾上腺皮质癌（ACC）是一种罕见的内分泌恶性肿瘤，具有高度突变异质性和普遍较差的临床预后。尽管 TP53、IGF-2 和 Wnt 信号通路的失调作用已被证实，但仍缺乏明确的遗传关联或独特的突变联系。最近的研究表明，表观遗传修饰在 ACC 的发生和/或进展中起着至关重要的作用。本研究特别评估了 RASSF1A 表观遗传沉默在肾上腺皮质恶性肿瘤中的潜在作用，RASSF1A 是最常沉默的肿瘤抑制基因。
使用肾上腺皮质肿瘤和正常组织标本，我们显示 RASSF1A mRNA 和蛋白在 ACC 中的表达显著降低。基于甲基化敏感和依赖限制性内切酶的 PCR 检测显示 RASSF1A 启动子的 DNA 超甲基化显著，提示 RASSF1A 沉默在 ACC 中存在表观遗传机制。相反，良性肾上腺皮质腺瘤（ACAs）中的 RASSF1A 启动子甲基化谱与正常肾上腺皮质非常相似。在 SW-13 ACC 细胞系中过表达异位 RASSF1A 降低了细胞的整体恶性行为，包括破坏穿过基底膜的侵袭、细胞迁移以及单细胞存活和生长。另一方面，RASSF1A/A133S 的表达，即 RASSF1A 的一种失活突变形式，未能在 ACC 细胞中引起类似的抑制恶性作用的反应。此外，在表达 RASSF1A 的 ACC 细胞和正常肾上腺皮质中 RASSF1A 与细胞骨架的关联表明 RASSF1A 在调节肾上腺皮质中的微管动力学中发挥作用，从而可能阻止恶性进展。
通过启动子甲基化下调 RASSF1A 可能在肾上腺皮质癌的恶性进展中发挥作用，可能通过阻断促进分化的 RASSF1A-微管相互作用来实现。
