Moriscot A S, Sayen M R, Hartong R, Wu P, Dillmann W H
Department of Medicine, University of California-San Diego, La Jolla 92093-0618, USA.
Endocrinology. 1997 Jan;138(1):26-32. doi: 10.1210/endo.138.1.4857.
Thyroid hormone (T3) increases the transcription of the sarcoplasmic reticulum Ca2+ adenosine triphosphatase (ATPase) gene (SERCA 2) through three thyroid hormone response elements. The existence of repetitive cis elements with different configurations is likely to serve specific functions such as interactions with nuclear transcription factors. In addition, the presence of different T3 receptor isoforms (T3Rs) may contribute to another level of complexity in providing specificity for T3 action. In this study, we investigated T3R alpha 1-vs. T3R beta 1-specific interactions with the myocyte enhancer-specific factor-2 (MEF-2) on the expression of the SERCA 2 gene in transient transfection assays in embryonal heart-derived H9c2 cells. MEF-2a in combination with either T3R alpha 1 or T3R beta 1 isoforms resulted in a 2.5-fold increase in SERCA 2 transgene expression in the absence of T3. Addition of T3 did not induce any further increase in SERCA 2 expression when T3R alpha 1 and MEF-2a expression vectors were cotransfected. In contrast, in the presence of T3R beta 1 and MEF-2, the addition of T3 increased chlorampenicol acetyltransferase activity by an additional 2.2-fold to a total 5.5-fold increase. The interaction between MEF-2a and T3R is transcription factor specific because another factor that binds to MEF-2 consensus sites (heart factor 1b) was not able to interact with T3R. In addition, MEF-2a failed to interact with other nuclear factors (cAMP response element-binding protein and Egr-1) that stimulate SERCA 2 gene transcription. In addition, we found that a single homologous thyroid hormone response element is not able to mediate the interactions between MEF-2a and T3Rs to increase SERCA 2 gene transcription. Our findings point to T3R isoform-specific interactions with a cell type-specific transcription factor (MEF-2) in the regulation of SERCA 2 gene expression.
甲状腺激素（T3）通过三个甲状腺激素反应元件增加肌浆网Ca2+腺苷三磷酸酶（ATP酶）基因（SERCA 2）的转录。具有不同构型的重复顺式元件的存在可能具有特定功能，如与核转录因子相互作用。此外，不同的T3受体亚型（T3Rs）的存在可能在为T3作用提供特异性方面增加了另一层次的复杂性。在本研究中，我们在胚胎心脏来源的H9c2细胞的瞬时转染试验中，研究了T3Rα1与T3Rβ1对肌细胞增强子特异性因子-2（MEF-2）与SERCA 2基因表达的特异性相互作用。在没有T3的情况下，MEF-2a与T3Rα1或T3Rβ1亚型结合导致SERCA 2转基因表达增加2.5倍。当T3Rα1和MEF-2a表达载体共转染时，添加T3并未导致SERCA 2表达进一步增加。相反，在存在T3Rβ1和MEF-2的情况下，添加T3使氯霉素乙酰转移酶活性额外增加2.2倍，总增加至5.5倍。MEF-2a与T3R之间的相互作用具有转录因子特异性，因为另一个与MEF-2共有位点结合的因子（心脏因子1b）不能与T3R相互作用。此外，MEF-2a未能与其他刺激SERCA 2基因转录的核因子（cAMP反应元件结合蛋白和Egr-1）相互作用。此外，我们发现单个同源甲状腺激素反应元件不能介导MEF-2a与T3Rs之间的相互作用以增加SERCA 2基因转录。我们的研究结果表明，在SERCA 2基因表达的调节中，T3R亚型与细胞类型特异性转录因子（MEF-2）存在特异性相互作用。
