Zuckerman Valentina, Lenos Kristiaan, Popowicz Grzegorz M, Silberman Isabelle, Grossman Tamar, Marine Jean-Christophe, Holak Tad A, Jochemsen Aart G, Haupt Ygal
Lautenberg Center for General and Tumor Immunology, The Hebrew University Hadassah Medical School, Jerusalem 91120, Israel.
J Biol Chem. 2009 Feb 6;284(6):4031-9. doi: 10.1074/jbc.M809211200. Epub 2008 Dec 15.
Upon exposure to DNA damage the p53 tumor suppressor is accumulated and activated to stall cellular growth. For this to occur, p53 must be relieved from its major inhibitors, Mdm2 (Hdm2 in humans) and Mdmx (Mdm4; Hdmx in humans). A key mechanism controlling this relief is the post-translational modifications of p53 and its inhibitors. We have previously demonstrated that the stress-activated tyrosine kinase, c-Abl, contributes to the relief of p53 from Hdm2. Because Hdmx is the major inhibitor of p53 activity, the additional possibility that c-Abl protects p53 through targeting Hdmx was explored in this study. c-Abl was found to interact with and to phosphorylate Hdmx. This phosphorylation was enhanced in response to DNA damage. Importantly, we mapped the sites of phosphorylation to the p53 binding domain of Hdmx. One of these phosphorylations, on tyrosine 99, inhibited Hdmx interaction with p53. This inhibition is consistent with the predicted role of this residue in the interaction with p53 based on the crystal structure of the interaction site. Our results show that c-Abl not only targets Hdm2, but also Hdmx, which together contribute to p53 activation in response to DNA damage.
在受到DNA损伤时，p53肿瘤抑制蛋白会积累并被激活，从而使细胞生长停滞。要实现这一点，p53必须从其主要抑制剂Mdm2（人类中的Hdm2）和Mdmx（Mdm4；人类中的Hdmx）中释放出来。控制这种释放的一个关键机制是p53及其抑制剂的翻译后修饰。我们之前已经证明，应激激活的酪氨酸激酶c-Abl有助于p53从Hdm2中释放出来。由于Hdmx是p53活性的主要抑制剂，因此在本研究中探讨了c-Abl通过靶向Hdmx来保护p53的额外可能性。研究发现c-Abl与Hdmx相互作用并使其磷酸化。这种磷酸化在DNA损伤时会增强。重要的是，我们将磷酸化位点定位到了Hdmx的p53结合结构域。其中一个磷酸化位点在酪氨酸99上，它抑制了Hdmx与p53的相互作用。这种抑制与基于相互作用位点晶体结构预测的该残基在与p53相互作用中的作用一致。我们的结果表明c-Abl不仅靶向Hdm2，还靶向Hdmx，它们共同促进了p53在DNA损伤时的激活。
