Regulation of vitamin A synthesis from carotenoids

描述（由申请人提供）：所有高等动物，包括人类，必须从饮食中获得维生素A，因为它们缺乏从头合成维生素A的能力。最终，所有维生素A都是由维生素A原类胡萝卜素形成的。维生素A原类胡萝卜素到维生素A的转化过程已经研究了40多年，尽管负责维生素A原类胡萝卜素到维生素A的裂解的酶的克隆和纯化直到最近才完成，当我们和其他人克隆和表征小鼠和人胡萝卜素裂解酶（CCE）时。发现CCE在整个身体中普遍表达，因此可能在向靶组织提供维生素A方面发挥一般作用。我们提出的研究的目标是了解控制肠道和肝脏中维生素A原转化为维生素A的调节机制。将探讨这一规定的两个方面。首先，我们将研究其他蛋白质对CCE活性的调节，可能是通过直接的蛋白质-蛋白质相互作用。已知细胞视黄醇结合蛋白（CRBP）与细胞内胡萝卜素裂解的产物retinal相互作用。将使用体外和体内技术检查CRBP对CCE活性的影响。此外，我们将探索CCE的直接下游酶，视网膜还原酶。我们已经确定了两个已知的短链脱氢酶/还原酶，retSDR和RalR 1，作为候选肠视网膜还原酶。这两种酶对从β-胡萝卜素生产视黄醇的作用将被深入探讨。最后，我们将研究hCCE表达的转录调控。在这里，我们建议检查的启动子的人CCE基因，以确定顺式调控元件和转录因子，结合到这些调控序列在这个基因。这些数据将为人类CCE基因的调控提供见解。总之，这些研究将提供全面的了解CCE活动在两个主要的组织部位，肠和肝。

DESCRIPTION (provided by applicant): All higher animals, including humans, must obtain vitamin A from the diet since they lack the ability to synthesize it de novo. Ultimately all vitamin A is formed from provitamin A carotenoids. The conversion process of provitamin A carotenoids to vitamin A has been studied for more than 4 decades although the cloning and purification of the enzyme responsible for the cleavage of provitamin A carotenoids to vitamin A were only recently accomplished when we and others cloned and characterized both mouse and human carotene cleavage enzyme (CCE). CCE was found to be ubiquitously expressed throughout the body and thus likely plays a general role in providing vitamin A to target tissues. The goal of our proposed studies is to understand the regulatory mechanisms controlling provitamin A conversion to vitamin A in intestine and liver. Two aspects of this regulation will be explored. First, we will examine the regulation of CCE activity by other proteins, possibly through direct protein-protein interactions. Cellular retinol-binding proteins (CRBPs) are known to interact with retinal, the product of carotene cleavage within cells. The effects of CRBPs on CCE activity will be examined using both in vitro and in vivo techniques. In addition, we will explore the direct down-stream enzyme to CCE, retinal reductase. We have identified two known short chain dehydrogenase/reductases, retSDR and RalR1, as candidate intestinal retinal reductases. The role of these two enzymes on retinol production from beta-carotene will be explored in depth. Finally, we will investigate the transcriptional regulation of hCCE expression. Here, we propose to examine the promoter of the human CCE gene to identify cis-regulatory elements and transcription factors that bind to these regulatory sequences in this gene. These data will provide insights into regulation of the CCE gene in humans. Taken together these studies will provide comprehensive understanding of CCE activity in two major tissue sites, intestine and liver.