Franklin C C, Sanchez V, Wagner F, Woodgett J R, Kraft A S
Division of Hematology/Oncology, University of Alabama, Birmingham 35294.
Proc Natl Acad Sci U S A. 1992 Aug 1;89(15):7247-51. doi: 10.1073/pnas.89.15.7247.
Phorbol ester tumor promoters activate gene transcription by regulating both the synthesis and posttranslational modification of the activator protein 1 (AP-1) transcription factor, c-Jun and JunB are components of the mammalian AP-1 complex. Here we demonstrate that in U-937 human leukemic cells, phorbol esters stimulate the phosphorylation of the amino terminus of human c-Jun (JUN) but not human JunB (JUNB). Mutational analysis indicates that serine-63 and -73, which reside within the putative regulatory domain of JUN, are required for both constitutive and phorbol 12-myristate 13-acetate-inducible N-terminal JUN phosphorylation. To determine the functional role of this N-terminal phosphorylation, we prepared several chimeric proteins containing the N-terminal 84 amino acids (positions 5-89) of human JUN or murine JUNB fused to the yeast GAL4 DNA-binding domain. This region was found to be sufficient for the phorbol ester-inducible transcriptional activity of JUN, but not JUNB. This induction was abolished by the mutation of serine-63 and -73 to leucine residues. Thus, we propose that phorbol esters enhance the trans-activation potential of JUN, but not JUNB, by the phosphorylation of the N-terminal regulatory domain of JUN.
佛波酯肿瘤启动子通过调节激活蛋白1（AP-1）转录因子的合成和翻译后修饰来激活基因转录，c-Jun和JunB是哺乳动物AP-1复合物的组成成分。在此我们证明，在U-937人白血病细胞中，佛波酯刺激人c-Jun（JUN）氨基末端的磷酸化，但不刺激人JunB（JUNB）的磷酸化。突变分析表明，位于JUN假定调节结构域内的丝氨酸-63和-73对于组成型和佛波醇12-肉豆蔻酸酯13-乙酸酯诱导的JUN氨基末端磷酸化都是必需的。为了确定这种氨基末端磷酸化的功能作用，我们制备了几种嵌合蛋白，这些蛋白包含与人JUN或鼠JUNB的氨基末端84个氨基酸（第5-89位）融合的酵母GAL4 DNA结合结构域。发现该区域对于JUN而非JUNB的佛波酯诱导的转录活性是足够的。将丝氨酸-63和-73突变为亮氨酸残基可消除这种诱导作用。因此，我们提出佛波酯通过JUN氨基末端调节结构域的磷酸化增强JUN而非JUNB的反式激活潜能。
