Leers J, Treuter E, Gustafsson J A
Center for Biotechnology, Department of Biosciences, Karolinska Institute, NOVUM, S-14157 Huddinge, Sweden.
Mol Cell Biol. 1998 Oct;18(10):6001-13. doi: 10.1128/MCB.18.10.6001.
Nuclear hormone receptors exert transcriptional activation of target genes upon hormone induction via interactions with the basal transcription machinery. This interaction is mediated by cofactors which physically bind to receptors, thereby acting as coactivators or corepressors leading to activation or repression, respectively. Here we report the screening for and cloning of a peroxisome proliferator receptor-interacting protein, the rat homolog of TIF2. By sequence comparison with the related coactivator SRC-1, we identified three short conserved motifs (NR boxes) in both proteins which are the putative binding sites of TIF2 to nuclear hormone receptors. We demonstrate here by generation of amino acid exchanges within the NR boxes that all three boxes located in the receptor interaction domain of TIF2 are necessary and sufficient for interaction. The three boxes individually can bind to hormone receptors but display preferences in binding for certain receptors. In addition, we show that the interaction domain of TIF2 can compete with other AF-2-dependent cofactors for binding to receptors. Finally, we demonstrate cooperative binding of two TIF2 molecules to a heterodimeric nuclear receptor complex even in the presence of only one cognate ligand, indicating an allosteric effect on the heterodimeric partner upon coactivator binding.
核激素受体通过与基础转录机制相互作用，在激素诱导下对靶基因发挥转录激活作用。这种相互作用由与受体物理结合的辅因子介导，这些辅因子分别作为共激活因子或共抑制因子，导致激活或抑制。在此，我们报告了过氧化物酶体增殖物激活受体相互作用蛋白（TIF2的大鼠同源物）的筛选和克隆。通过与相关共激活因子SRC-1的序列比较，我们在这两种蛋白质中鉴定出三个短保守基序（NR框），它们是TIF2与核激素受体的假定结合位点。我们在此通过在NR框内进行氨基酸交换证明，位于TIF2受体相互作用结构域中的所有三个框对于相互作用都是必需且充分的。这三个框各自都能与激素受体结合，但对某些受体的结合表现出偏好。此外，我们表明TIF2的相互作用结构域可以与其他AF-2依赖性辅因子竞争与受体的结合。最后，我们证明即使仅存在一种同源配体，两个TIF2分子也能与异二聚体核受体复合物协同结合，这表明共激活因子结合对异二聚体伴侣具有变构效应。
