Zhou Yunli, Zhong Ying, Wang Yingying, Zhang Xun, Batista Dalia L, Gejman Roger, Ansell Peter J, Zhao Jing, Weng Catherine, Klibanski Anne
Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
J Biol Chem. 2007 Aug 24;282(34):24731-42. doi: 10.1074/jbc.M702029200. Epub 2007 Jun 13.
MEG3 is a maternally expressed imprinted gene suggested to function as a non-coding RNA. Our previous studies suggest that MEG3 has a function of tumor suppression. The tumor suppressor p53 plays a central role in tumor suppression and mediates the functions of many other tumor suppressors. Therefore, we hypothesized that MEG3 functions through activation of p53. We found that transfection of expression constructs for MEG3 and its isoforms results in a significant increase in p53 protein levels and dramatically stimulates p53-dependent transcription from a p53-responsive promoter. Using this as the functional assay, we demonstrated that the open reading frames encoded by MEG3 transcripts are not required for MEG3 function, and the folding of MEG3 RNA is critical to its function, supporting the concept that MEG3 functions as a non-coding RNA. We further found that MEG3 stimulates expression of the growth differentiation factor 15 (GDF15) by enhancing p53 binding to the GDF15 gene promoter. Interestingly, MEG3 does not stimulate p21(CIP1) expression, suggesting that MEG3 can regulate the specificity of p53 transcriptional activation. p53 degradation is mainly mediated by the mouse double minute 2 homolog (MDM2). We found that MDM2 levels were down-regulated in cells transfected with MEG3, suggesting that MDM2 suppression contributes at least in part to p53 accumulation induced by MEG3. Finally, we found that MEG3 is able to inhibit cell proliferation in the absence of p53. These data suggest that MEG3 non-coding RNA may function as a tumor suppressor, whose action is mediated by both p53-dependent and p53-independent pathways.
MEG3是一个母系表达的印记基因，被认为作为一种非编码RNA发挥作用。我们之前的研究表明MEG3具有肿瘤抑制功能。肿瘤抑制因子p53在肿瘤抑制中起核心作用，并介导许多其他肿瘤抑制因子的功能。因此，我们推测MEG3通过激活p53发挥作用。我们发现转染MEG3及其异构体的表达构建体会导致p53蛋白水平显著增加，并显著刺激来自p53反应性启动子的p53依赖性转录。以此作为功能测定，我们证明MEG3功能不需要MEG3转录本编码的开放阅读框，并且MEG3 RNA的折叠对其功能至关重要，这支持了MEG3作为非编码RNA发挥作用的概念。我们进一步发现MEG3通过增强p53与生长分化因子15（GDF15）基因启动子的结合来刺激GDF15的表达。有趣的是，MEG3不刺激p21（CIP1）的表达，这表明MEG3可以调节p53转录激活的特异性。p�3的降解主要由小鼠双微体2同源物（MDM2）介导。我们发现用MEG3转染的细胞中MDM2水平下调，这表明MDM2的抑制至少部分促成了MEG3诱导的p53积累。最后，我们发现MEG3在没有p53的情况下能够抑制细胞增殖。这些数据表明MEG3非编码RNA可能作为一种肿瘤抑制因子发挥作用，其作用由p53依赖性和p53非依赖性途径介导。
