Hormel Institute, University of Minnesota, Austin, Minnesota 55912, USA.
J Biol Chem. 2011 Jan 21;286(3):2057-66. doi: 10.1074/jbc.M110.147306. Epub 2010 Nov 22.
RSK2 is a widely expressed serine/threonine kinase, and its activation enhances cell proliferation. Here, we report that ATF1 is a novel substrate of RSK2 and that RSK2-ATF1 signaling plays an important role in EGF-induced neoplastic cell transformation. RSK2 phosphorylated ATF1 at Ser-63 and enhanced ATF1 transcriptional activity. Docking experiments using the crystal structure of the RSK2 N-terminal kinase domain combined with in vitro pulldown assays demonstrated that eriodictyol, a flavanone found in fruits, bound with the N-terminal kinase domain of RSK2 to inhibit RSK2 N-terminal kinase activity. In cells, eriodictyol inhibited phosphorylation of ATF1 but had no effect on the phosphorylation of RSK, MEK1/2, ERK1/2, p38 or JNKs, indicating that eriodictyol specifically suppresses RSK2 signaling. Furthermore, eriodictyol inhibited RSK2-mediated ATF1 transactivation and tumor promoter-induced transformation of JB6 Cl41 cells. Eriodictyol or knockdown of RSK2 or ATF1 also suppressed Ras-mediated focus formation. Overall, these results indicate that RSK2-ATF1 signaling plays an important role in neoplastic cell transformation and that eriodictyol is a novel natural compound for suppressing RSK2 kinase activity.
RSK2 是一种广泛表达的丝氨酸/苏氨酸激酶，其激活增强细胞增殖。在这里，我们报告 ATF1 是 RSK2 的一种新底物，RSK2-ATF1 信号在 EGF 诱导的肿瘤细胞转化中发挥重要作用。RSK2 在 Ser-63 位点磷酸化 ATF1 并增强 ATF1 的转录活性。使用 RSK2 N 端激酶结构域的晶体结构结合体外下拉实验进行对接实验表明，桔皮素是一种存在于水果中的黄烷酮，与 RSK2 的 N 端激酶结构域结合，抑制 RSK2 N 端激酶活性。在细胞中，桔皮素抑制 ATF1 的磷酸化，但对 RSK、MEK1/2、ERK1/2、p38 或 JNKs 的磷酸化没有影响，表明桔皮素特异性抑制 RSK2 信号。此外，桔皮素抑制 RSK2 介导的 ATF1 反式激活和 JB6 Cl41 细胞中肿瘤促进剂诱导的转化。桔皮素或敲低 RSK2 或 ATF1 也抑制 Ras 介导的焦点形成。总的来说，这些结果表明 RSK2-ATF1 信号在肿瘤细胞转化中发挥重要作用，桔皮素是一种新型抑制 RSK2 激酶活性的天然化合物。
