Rascle A, Ghysdael J, Samarut J
Laboratoire de Biologie Moléculaire et Cellulaire, CNRS UMR49, INRA, Ecole Normale Supérieure de Lyon, France.
Oncogene. 1994 Oct;9(10):2853-67.
The carbonic anhydrase II (CAII) gene is the only known gene identified as direct target for v-ErbA-mediated repression in avian erythroleukemic cells transformed by Avian Erythroblastosis Virus (AEV). This gene is transcriptionally activated by thyroid hormone (T3) in normal erythrocytic cells. In this work we have analysed the molecular basis of the transcriptional control of the CAII gene by c-ErbA and v-ErbA. We show that several domains in the promoter control hormonal regulation of transcription. One domain proximal to the TATA box mediates T3 response but contains no identified binding site for c-ErbA. An other domain termed PAL2 is approximately 600 bp upstream the transcription initiation site and contains a c-ErbA binding site. We show that when it is associated to a heterologous promoter this site mediates transcriptional repression in erythrocytic cells but not in HeLa cells. Moreover, this site binds a nuclear erythrocyte-specific factor that we called NFX, which is different from c-ErbA. heterodimers between c-ErbA and the 9-cis retinoic acid receptor (RXR) compete with NFX for binding to PAL2. In contrast, v-ErbA alone or in association with RXR is a very poor competitor and is unable to chase NFX out of the PAL2 site. We propose that NFX is a transcription repressor whose activity is inhibited by c-ErbA but not v-ErbA. This mechanism might contribute to the overall regulation of the carbonic anhydrase II promoter. These data illustrate another possible mechanism through which v-ErbA might antagonize the function of c-ErbA in controlling gene expression.
碳酸酐酶II（CAII）基因是唯一已知的被确定为禽成红细胞白血病病毒（AEV）转化的禽成红细胞白血病细胞中v-ErbA介导的抑制作用直接靶点的基因。该基因在正常红细胞细胞中由甲状腺激素（T3）转录激活。在这项工作中，我们分析了c-ErbA和v-ErbA对CAII基因转录控制的分子基础。我们表明，启动子中的几个结构域控制转录的激素调节。靠近TATA框的一个结构域介导T3反应，但未发现c-ErbA的结合位点。另一个称为PAL2的结构域位于转录起始位点上游约600 bp处，包含一个c-ErbA结合位点。我们表明，当它与异源启动子相关联时，该位点在红细胞细胞中介导转录抑制，但在HeLa细胞中不介导。此外，该位点结合一种我们称为NFX的核红细胞特异性因子，它与c-ErbA不同。c-ErbA和9-顺式视黄酸受体（RXR）之间的异二聚体与NFX竞争结合PAL2。相反，单独的v-ErbA或与RXR结合时是一个非常弱的竞争者，无法将NFX从PAL2位点驱逐出去。我们提出NFX是一种转录抑制因子，其活性被c-ErbA抑制，但不被v-ErbA抑制。这种机制可能有助于碳酸酐酶II启动子的整体调节。这些数据说明了v-ErbA可能在控制基因表达中拮抗c-ErbA功能的另一种可能机制。
