Oleinik N V, Krupenko N I, Krupenko S A
Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
Oncogene. 2007 Nov 8;26(51):7222-30. doi: 10.1038/sj.onc.1210526. Epub 2007 May 21.
FDH (10-formyltetrahydrofolate dehydrogenase) is strongly downregulated in tumors while its elevation suppresses proliferation of cancer cells and induces p53-dependent apoptosis. We have previously shown that FDH induces phosphorylation of p53 at Ser6, which is a required step in the activation of apoptosis. In the present study, we report that FDH-induced p53 phosphorylation is carried out by JNK1 and JNK2 (c-Jun N-terminal kinases) working in concert. We have demonstrated that FDH induces phosphorylation of JNK1 and JNK2, while treatment of FDH-expressing cells with JNK inhibitor SP600125, as well as knockdown of JNK1 or JNK2 by siRNA, prevents phosphorylation of p53 at Ser6 and protects cells from apoptosis. Interestingly, the knockdown of JNK1 abolished phosphorylation of JNK2 in response to FDH, while knockdown of JNK2 did not prevent JNK1 phosphorylation. Pull-down assay with the p53-specific antibody has shown that JNK2, but not JNK1, is physically associated with p53. Our studies revealed a novel mechanism in which phosphorylation of JNK2 is mediated by JNK1 before phosphorylation of p53, and then p53 is directly phosphorylated by JNK2 at Ser6.
10-甲酰四氢叶酸脱氢酶（FDH）在肿瘤中强烈下调，而其表达升高可抑制癌细胞增殖并诱导p53依赖性凋亡。我们之前已经表明，FDH可诱导p53在Ser6位点磷酸化，这是激活凋亡的必要步骤。在本研究中，我们报告FDH诱导的p53磷酸化是由协同作用的JNK1和JNK2（c-Jun氨基末端激酶）完成的。我们已经证明，FDH可诱导JNK1和JNK2磷酸化，而用JNK抑制剂SP600125处理表达FDH的细胞，以及通过siRNA敲低JNK1或JNK2，均可阻止p53在Ser6位点磷酸化并保护细胞免于凋亡。有趣的是，敲低JNK1可消除FDH诱导的JNK2磷酸化，而敲低JNK2并不能阻止JNK1磷酸化。用p53特异性抗体进行的下拉实验表明，与p53发生物理相互作用的是JNK2，而非JNK1。我们的研究揭示了一种新机制，即JNK2的磷酸化在p53磷酸化之前由JNK1介导，然后p53在Ser6位点被JNK2直接磷酸化。
