Inhibitor of Normal Growth (ING)

小鼠双分钟2(MDM2)的抑制剂Nutlin-3a能够激活P53，导致P53调控的过程，如细胞凋亡和细胞生长停滞。我们发现，在正常人成纤维细胞中，细胞过早衰老是由Nutlin-3a介导的内源性P53功能激活引起的一种表型。在Nutlin-3a诱导的细胞衰老过程中，miR-34家族(miR-34a、miR-34b和miR-34c)以p53依赖的方式上调，提示内源性表达的miR-34家族在细胞衰老调控中具有重要的生理意义。在Nutlin-3a改变表达的蛋白编码基因中，我们选择了ING2作为进一步研究的基因；这是我们以前研究过的基因。P53直接与ING2基因启动子结合，在转录上抑制ING2基因启动子。在人成纤维细胞中，ING2的siRNA敲除与Nutlin-3a治疗一样有效地诱导细胞衰老。虽然Nutlin-3a诱导的衰老依赖于P53，但ING2基因敲除甚至在P53缺失的情况下也会导致衰老，这表明ING2是Nutin-3a诱导的、P53介导的细胞衰老信号的下游效应器。我们的研究表明，P53和ING2在衰老调节中的功能相互作用有两个不同的方面：(A)ING2活性的增强通过翻译后激活P53来诱导衰老；(B)在非应激条件下，ING2的内源水平限制了P53的激活，而不是P53的激活。

Nutlin-3a, an inhibitor of murine double minute 2(MDM2), has the ability to activate p53, leading to p53-regulated processes such as apoptosis and cell growth arrest. We found that premature cellular senescence was a phenotype induced by Nutlin-3a-mediated activation of endogenouse p53 functions in normal human fibroblasts. The miR-34 families of microRNAs (miR-34a, miR-34b and miR-34c) were upregulated with the Nutlin-3a-induced senescence in a p53-dependent manner, suggesting the physiological importance of the endogenously expressed miR-34 family in the regulation of cellular senescence. Among the protein-coding genes which were altered in expression by Nutlin-3a, we selected ING2 for further study; a gene we studied previously. p53 directly bound to the ING2 gene promoter to transcriptionally repress it. The siRNA knockdown of ING2 induced cellular senescence as effectively as Nutlin-3a treatment in human fibroblasts. While the Nutlin-3a-induced senescence was p53-dependent, the ING2 knockdown caused senescence even in the abscence of p53, suggesting that ING2 is a downstream effector of Nutlin-3a-induced, p53-mediated signaling to cellular senescence. Two different facets of the functional interplay between p53 and ING2 in the regulation of senescence are suggested by our studies: (a) the enhanced activity of ING2 induces senescence by post-translationally activating p53; and (b) the endogenous levels of ING2 restricts senescence under non-stressed conditions without p53 activation.