The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun 130024, China.
J Genet Genomics. 2013 Aug 20;40(8):391-8. doi: 10.1016/j.jgg.2013.05.007. Epub 2013 Jun 12.
Cellular senescence is an irreversible form of cell cycle arrest that provides a barrier to neoplastic transformation. The integrity of the Rb (Retinoblastoma) pathway is necessary for the formation of the senescence-associated heterochromatin foci (SAHF) that offers a molecular basis for the stability of the senescent state. Surprisingly, although high mobility group A2 protein (HMGA2) can promote tumorigenesis and inhibit Rb function in tumor cells, high-level expression of HMGA2 is sufficient to induce SAHF formation in primary cells. It therefore becomes significant to determine whether Rb protein is necessary in HMGA2-induced SAHF formation. In this study, we established the cellular senescence and SAHF assembly WI38 cell model by ectopic expression of HMGA2, in which typical senescent markers were seen, including notable upregulation of p53, p21 and p16, and elevated SA-β-galactosidase staining together with downregulation of E2F target genes. We then showed that the Rb pathway inhibitor E7 protein was able to partly abolish the ability of SAHF formation after HMGA2 expression in WI38 cells, indicating that Rb is a crucial factor for HMGA2-induced SAHF formation. However, Rb depletion did not completely rescue the cell growth arrest induced by HMGA2, suggesting that Rb is not an exclusive pathway for HMGA2-induced senescence in WI38 cells.
细胞衰老（cellular senescence）是一种不可逆的细胞周期停滞形式，为肿瘤转化提供了障碍。Rb（视网膜母细胞瘤）通路的完整性对于衰老相关异染色质焦点（senescence-associated heterochromatin foci，SAHF）的形成是必要的，SAHF 为衰老状态的稳定性提供了分子基础。令人惊讶的是，尽管高迁移率族 A2 蛋白（high mobility group A2 protein，HMGA2）可以促进肿瘤发生并抑制肿瘤细胞中的 Rb 功能，但高水平的 HMGA2 表达足以诱导原代细胞中 SAHF 的形成。因此，确定 HMGA2 诱导的 SAHF 形成是否需要 Rb 蛋白变得非常重要。在这项研究中，我们通过异位表达 HMGA2 建立了 WI38 细胞的细胞衰老和 SAHF 组装模型，其中观察到典型的衰老标志物，包括 p53、p21 和 p16 的显著上调，SA-β-半乳糖苷酶染色增加，以及 E2F 靶基因下调。然后，我们表明 Rb 通路抑制剂 E7 蛋白能够部分消除 HMGA2 表达后 WI38 细胞中 SAHF 形成的能力，表明 Rb 是 HMGA2 诱导 SAHF 形成的关键因素。然而，Rb 缺失并没有完全挽救 HMGA2 诱导的细胞生长停滞，这表明 Rb 不是 HMGA2 诱导 WI38 细胞衰老的唯一途径。
