Centre de recherche du Centre hospitalier de l'Université de Montréal and Institut du cancer de Montréal, Montréal, Québec, Canada.
PLoS One. 2012;7(2):e31916. doi: 10.1371/journal.pone.0031916. Epub 2012 Feb 15.
In vitro, cellular immortalization and transformation define a model for multistep carcinogenesis and current ongoing challenges include the identification of specific molecular events associated with steps along this oncogenic pathway. Here, using NIH3T3 cells, we identified transcriptionally related events associated with the expression of Polyomavirus Large-T antigen (PyLT), a potent viral oncogene. We propose that a subset of these alterations in gene expression may be related to the early events that contribute to carcinogenesis. The proposed tumor suppressor Necdin, known to be regulated by p53, was within a group of genes that was consistently upregulated in the presence of PyLT. While Necdin is induced following p53 activation with different genotoxic stresses, Necdin induction by PyLT did not involve p53 activation or the Rb-binding site of PyLT. Necdin depletion by shRNA conferred a proliferative advantage to NIH3T3 and PyLT-expressing NIH3T3 (NIHLT) cells. In contrast, our results demonstrate that although overexpression of Necdin induced a growth arrest in NIH3T3 and NIHLT cells, a growing population rapidly emerged from these arrested cells. This population no longer showed significant proliferation defects despite high Necdin expression. Moreover, we established that Necdin is a negative regulator of p53-mediated growth arrest induced by nutlin-3, suggesting that Necdin upregulation could contribute to the bypass of a p53-response in p53 wild type tumors. To support this, we characterized Necdin expression in low malignant potential ovarian cancer (LMP) where p53 mutations rarely occur. Elevated levels of Necdin expression were observed in LMP when compared to aggressive serous ovarian cancers. We propose that in some contexts, the constitutive expression of Necdin could contribute to cancer promotion by delaying appropriate p53 responses and potentially promote genomic instability.
在体外，细胞永生化和转化定义了多步骤致癌的模型，当前正在进行的挑战包括确定与致癌途径中这一步骤相关的特定分子事件。在这里，我们使用 NIH3T3 细胞，鉴定了与 Polyomavirus Large-T 抗原（PyLT）表达相关的转录相关事件，PyLT 是一种有效的病毒癌基因。我们提出，这些基因表达的改变中的一部分可能与导致癌变的早期事件有关。已知受 p53 调控的肿瘤抑制因子 Necdin，是一组在存在 PyLT 时持续上调的基因之一。虽然 Necdin 在不同的遗传毒性应激下被 p53 激活诱导，但 PyLT 诱导 Necdin 不涉及 p53 激活或 PyLT 的 Rb 结合位点。通过 shRNA 耗尽 Necdin 赋予 NIH3T3 和表达 PyLT 的 NIH3T3（NIHLT）细胞增殖优势。相比之下，我们的结果表明，尽管 Necdin 的过表达诱导 NIH3T3 和 NIHLT 细胞生长停滞，但这些停滞的细胞中迅速出现了一个生长的群体。尽管 Necdin 表达很高，但该群体不再表现出明显的增殖缺陷。此外，我们确定 Necdin 是 Nutlin-3 诱导的 p53 介导的生长停滞的负调节剂，表明 Necdin 的上调可能有助于绕过 p53 野生型肿瘤中的 p53 反应。为了支持这一点，我们在低恶性潜能卵巢癌（LMP）中对 Necdin 表达进行了特征分析，其中 p53 突变很少发生。与侵袭性浆液性卵巢癌相比，LMP 中观察到 Necdin 表达水平升高。我们提出，在某些情况下，Necdin 的组成型表达可能通过延迟适当的 p53 反应来促进癌症的发生，并可能促进基因组不稳定性。
