Molecular mechanism of the transcription regulation by the retinoic acid receptor in human salivary gland cell line HSG.

视黄酸（retinoic acid， RA）可调节HSG细胞的生长。近年来研究发现，在RA信号传导过程中，视黄酸受体（RAR）与creb结合蛋白（CBP）和p160家族成员蛋白等共激活因子相互作用，促进核心转录因子接近DNA。为了研究共激活因子与HSG细胞RA信号的关系，我们检测了共激活因子的表达。免疫沉淀和western blotting显示CBP和类固醇受体共激活因子1 （SRC 1）的表达，SRC 1具有组蛋白乙酰转移酶的活性。在HSG细胞中，过表达CBP可使ra依赖性转录激活增加约10倍。转染CBP的反义寡核苷酸抑制了这种反活化的增加。这些发现表明，在HSG细胞中表达的CBP与RARs一起介导了生长调节的转录激活。我们已经克隆了coup -转录因子I （COUP-TFI）的DNA片段。本研究采用RT-PCR和western blotting方法证实了全长COUP-TFI的表达。为了确定COUP-TFI在RA信号传导中的作用，我们检查了报告基因分析。COUP-TFI的过表达抑制了ra诱导的报告基因的转录激活。使用染色质集成稳定转染的报告基因系统也显示了类似的结果。COUP-TFI的反义寡核苷酸通过[^3H]胸腺嘧啶掺入来抑制ra依赖性的生长抑制。从这些结果来看，COUP-TFI很可能通过抑制ra诱导的反激活来调节ra敏感过程，如细胞的增殖或分化。

Growth of HSG cells is regulated by retinoic acid (RA). Recently, it has been revealed that, in the process of RA signaling, retinoic acid receptors (RAR) interact with coactivators such as CREB-binding protein (CBP) and p160 family member proteins, which facilitates the access of core transcription factors to the DNA.To investigate the relationship of coactivators to the RA signaling in HSG cells, we examined the expression of coactivators. Immunoprecipitation and western blotting revealed the expression of CBP and steroid receptor coactivator 1 (SRC 1), which exhibited the activity of histone acetyltransferase. The overexpression of CBP in HSG cell strongly increased the RA-dependent transcription activation approximately 10-fold. This increase of the transactivation was inhibited by the transfection of the antisense oligonucleotide for CBP.These findings suggest that CBP expressed in HSG cells mediates the growth-regulating transcription activation in concert with RARs.We have previously cloned the DNA fragment of COUP-transcription factor I (COUP-TFI). In this study, the expression of full length COUP-TFI was confirmed by use of RT-PCR and western blotting. To determine the role of COUP-TFI in the RA signaling, the reporter gene analysis was examined. The overexpression of COUP-TFI suppressed the RA-induced transcription activation of the reporter gene. Similar results were shown using a chromatin-integrated stably-transfected reporter gene system. The antisense oligonucleotide for COUP-TFI squelched the RA-dependent growth inhibition which was measured by the [^3H]thymidine incorporation. From these results, COUP-TFI very likely regulates RA-sensitive processes such as proliferation or differentiation of the cells by repressing the RA-induced transactivation.