Cosgaya J M, Aranda A
Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, Madrid, Spain.
J Neurochem. 2001 Feb;76(3):661-71. doi: 10.1046/j.1471-4159.2001.00078.x.
Nerve growth factor (NGF) and retinoic acid (RA) exert important actions on PC12 cells. We have previously shown that incubation with NGF induces retinoic acid receptor beta (RARbeta) binding to a hormone response element in PC12 cells. In this study we show that NGF increases RARbeta protein levels by enhancing basal RARbeta2 promoter activity, and potentiates stimulation by RA in transient transfection assays. The effect of RA is mediated by a RA response element (RARE) located at -37/-53 and mutation of this element abolishes activation by the retinoid, as well as cooperation with NGF. However, the action of NGF is independent of the RARE and is mediated by sequences overlapping the TATA box and the INR comprising nucleotides -59 to +14. NGF produces a strong decrease in some of the complexes that bind to the INR. These results suggest that the RARbeta2 gene could be in a basal repressed state and NGF could increase RARbeta2 transcription by inducing the release of some inhibitory factors from the INR. Functional Ras is required for RARbeta2 promoter activation by NGF because expression of oncogenic Ras increases promoter activity and a dominant inhibitory Ras mutant blocks the effect of NGF. Oncogenic Raf also mimics the effect of NGF on the promoter. Other ligands of tyrosine kinase receptors that stimulate Ras also cause RARbeta2 promoter activation and act cooperatively with RA. These results indicate the existence of cross-coupling of the Ras-Raf signal transduction pathway with retinoid receptor pathways which could increase sensitivity to RA and be important for PC12 cell function.
神经生长因子（NGF）和视黄酸（RA）对PC12细胞发挥重要作用。我们之前已经表明，用NGF孵育可诱导视黄酸受体β（RARβ）与PC12细胞中的激素反应元件结合。在本研究中我们发现，NGF通过增强基础RARβ2启动子活性来增加RARβ蛋白水平，并在瞬时转染实验中增强RA的刺激作用。RA的作用由位于-37 / -53的视黄酸反应元件（RARE）介导，该元件的突变消除了类视黄醇的激活作用以及与NGF的协同作用。然而，NGF的作用独立于RARE，由与TATA盒和包含核苷酸-59至+14的起始子重叠的序列介导。NGF使一些与起始子结合的复合物显著减少。这些结果表明，RARβ2基因可能处于基础抑制状态，NGF可能通过诱导从起始子释放一些抑制因子来增加RARβ2转录。功能性Ras是NGF激活RARβ2启动子所必需的，因为致癌性Ras的表达增加启动子活性，而显性抑制性Ras突变体可阻断NGF的作用。致癌性Raf也模拟NGF对启动子的作用。刺激Ras的酪氨酸激酶受体的其他配体也会导致RARβ2启动子激活，并与RA协同作用。这些结果表明存在Ras - Raf信号转导途径与类视黄醇受体途径的交叉偶联，这可能会增加对RA的敏感性，并且对PC12细胞功能很重要。
