Folkers G E, van der Saag P T
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht, The Netherlands.
Mol Cell Biol. 1995 Nov;15(11):5868-78. doi: 10.1128/MCB.15.11.5868.
Transcription regulation by DNA-bound activators is thought to be mediated by a direct interaction between these proteins and TATA-binding protein (TBP), TFIIB, or TBP-associated factors, although occasionally cofactors or adapters are required. For ligand-induced activation by the retinoic acid receptor-retinoid X receptor (RAR-RXR) heterodimer, the RAR beta 2 promoter is dependent on the presence of E1A or E1A-like activity, since this promoter is activated by retinoic acid only in cells expressing such proteins. The mechanism underlying this E1A requirement is largely unknown. We now show that direct interaction between RAR and E1A is a requirement for retinoic acid-induced RAR beta 2 activation. The activity of the hormone-dependent activation function 2 (AF-2) of RAR beta is upregulated by E1A, and an interaction between this region and E1A was observed, but not with AF-1 or AF-2 of RXR alpha. This interaction is dependent on conserved region III (CRIII), the 13S mRNA-specific region of E1A. Deletion analysis within this region indicated that the complete CRIII is needed for activation. The putative zinc finger region is crucial, probably as a consequence of interaction with TBP. Furthermore, the region surrounding amino acid 178, partially overlapping with the TBP binding region, is involved in both binding to and activation by AF-2. We propose that E1A functions as a cofactor by interacting with both TBP and RAR, thereby stabilizing the preinitiation complex.
人们认为，与DNA结合的激活因子对转录的调控是通过这些蛋白质与TATA结合蛋白（TBP）、TFIIB或TBP相关因子之间的直接相互作用介导的，不过偶尔也需要辅因子或衔接蛋白。对于视黄酸受体-类视黄醇X受体（RAR-RXR）异二聚体介导的配体诱导激活，RARβ2启动子依赖于E1A或E1A样活性的存在，因为该启动子仅在表达此类蛋白质的细胞中被视黄酸激活。这种对E1A需求的潜在机制在很大程度上尚不清楚。我们现在表明，RAR与E1A之间的直接相互作用是视黄酸诱导RARβ2激活所必需的。E1A上调了RARβ激素依赖性激活功能2（AF-2）的活性，并且观察到该区域与E1A之间存在相互作用，但与RXRα的AF-1或AF-2没有相互作用。这种相互作用依赖于E1A的保守区域III（CRIII），即13S mRNA特异性区域。该区域内的缺失分析表明，完整的CRIII是激活所必需的。推定的锌指区域至关重要，可能是与TBP相互作用的结果。此外，与TBP结合区域部分重叠的氨基酸178周围区域，参与了与AF-2的结合和激活。我们提出，E1A通过与TBP和RAR相互作用而作为辅因子发挥作用，从而稳定起始前复合物。
