Khanna Hemant, Akimoto Masayuki, Siffroi-Fernandez Sandrine, Friedman James S, Hicks David, Swaroop Anand
Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan 48105, USA, and Translational Research Center, Kyoto University Hospital, Japan.
J Biol Chem. 2006 Sep 15;281(37):27327-34. doi: 10.1074/jbc.M605500200. Epub 2006 Jul 19.
NRL (neural retina leucine zipper) is a key basic motif-leucine zipper (bZIP) transcription factor, which orchestrates rod photoreceptor differentiation by activating the expression of rod-specific genes. The deletion of Nrl in mice results in functional cones that are derived from rod precursors. However, signaling pathways modulating the expression or activity of NRL have not been elucidated. Here, we show that retinoic acid (RA), a diffusible factor implicated in rod development, activates the expression of NRL in serum-deprived Y79 human retinoblastoma cells and in primary cultures of rat and porcine photoreceptors. The effect of RA is mimicked by TTNPB, a RA receptor agonist, and requires new protein synthesis. DNaseI footprinting and electrophoretic mobility shift assays (EMSA) using bovine retinal nuclear extract demonstrate that RA response elements (RAREs) identified within the Nrl promoter bind to RA receptors. Furthermore, in transiently transfected Y79 and HEK293 cells the activity of Nrl-promoter driving a luciferase reporter gene is induced by RA, and this activation is mediated by RAREs. Our data suggest that signaling by RA via RA receptors regulates the expression of NRL, providing a framework for delineating early steps in photoreceptor cell fate determination.
NRL（神经视网膜亮氨酸拉链）是一种关键的碱性模体-亮氨酸拉链（bZIP）转录因子，它通过激活视杆特异性基因的表达来协调视杆光感受器的分化。小鼠中Nrl的缺失会导致源自视杆前体的功能性视锥细胞。然而，调节NRL表达或活性的信号通路尚未阐明。在这里，我们表明视黄酸（RA），一种与视杆发育有关的可扩散因子，在血清饥饿的Y79人视网膜母细胞瘤细胞以及大鼠和猪光感受器的原代培养物中激活NRL的表达。RA的作用可被RA受体激动剂TTNPB模拟，并且需要新的蛋白质合成。使用牛视网膜核提取物进行的DNaseI足迹分析和电泳迁移率变动分析（EMSA）表明，在Nrl启动子内鉴定出的视黄酸反应元件（RAREs）与RA受体结合。此外，在瞬时转染的Y79和HEK293细胞中，驱动荧光素酶报告基因的Nrl启动子的活性被RA诱导，并且这种激活是由RAREs介导的。我们的数据表明，RA通过RA受体发出的信号调节NRL的表达，为描绘光感受器细胞命运决定的早期步骤提供了一个框架。
