Transcriptional coactivator UTF1 as an embryonic stem cell cofactor for retinoic acid receptor

胚胎癌（EC）细胞系如F9和P19细胞被广泛用作研究哺乳动物早期发育阶段的分子基础的模型系统。EC细胞具有许多类似于早期胚胎细胞的特性。例如，这些EC细胞保留多能性，可以通过维甲酸和/或聚集体形成诱导分化为几种类型的细胞，如肌肉和神经细胞。在EC细胞中进行的早期研究清楚地表明，这些细胞具有许多有趣和独特的调节特征。其中一个例子是关于维甲酸受体(RAR) β2基因表达的调控。该基因的启动子携带两个RAR反应元件（RARE），其活性由自身基因自动调节。然而，研究表明，该基因的表达需要一个额外的胚胎干细胞辅助因子。1998年，我分子克隆了一个新的转录物。更多的辅助激活因子UTF1，其表达仅限于早期胚胎细胞。当我仔细观察氨基酸序列时，我发现该蛋白在一个进化保守结构域中含有两个LxxLL基序，该结构域通常存在于核受体辅助因子（如SRC-1和TIF-2）中，并被证明参与与核受体的相互作用。因此，我推测UTF1可能对应于RARβ2基因表达所需的胚胎干细胞特异性辅因子。通过瞬时转染，我证明了UTF1能够刺激该启动子的转录。此外，我发现这种转录激活是通过RARE发生的。我还通过GST下拉实验证明，UTF1能够直接与RAR结合。然而，发现这种相互作用独立于视黄酸和RAR的AF2结构域。因此，UTF1与RAR结合的方式与其他核受体辅助因子（如SRC-1和TIF-2）不同。少

Embryonic carcinoma (EC) cell lines such as F9 and P19 cells are widely used as a model system for studying the molecular basis governing early developmental stages of mammals. The EC cells possess a number of properties which resemble those of early embryonic cells. For example, these EC cells retain pluripotent properties and can be induced to differentiate into several types of cells such as muscle and nerve cells using retinoic acid and/or by aggregate formation. Early studies carried out in EC cells clearly indicated that these cells have a number of interesting and unique regulatory features. One of such examples is that about the regulation of retinoic acid receptor (RAR) β2 gene expression. The promoter of this gene carries two RAR responsive element (RARE) and its activity is autoregulated by its own gene. However, it has been demonstrated that the gene requires an additional embryonic stem cell cofactor for its expression..In 1998, I have molecularly cloned a novel transcript … More ional coactivator UTF1 whose expression is restricted to early embryonic cells. When I looked the amino acid sequence carefully, I found that the protein contains two LxxLL motif in the one of the evolutionarily conserved domain which is commonly present in nuclear receptor cofactor such as SRC-1 and TIF-2 and is demonstrated to be involved in the interaction with nuclear receptor. Therefore, I hypothesized that the UTF1 may correspond to the embyonic stem cell specific cofactor required for RARβ2 gene expression. By the transient transfection, I demonstrated that UTF1 is able to stimulate transcription from this promoter. Furthermore, I found that this activation of transcription is occurred through the RARE.I also demonstrated, by GST pull down assay, that UTF1 is able to bind to RAR directly. However, this interaction is found to be independent of retinoic acid and AF2 domain of the RAR.Thus, the UTF1 appears to bind to RAR in a distinct way from other nuclear receptor cofactors such as SRC-1 and TIF-2. Less