REGULATION OF THE SECRETION OF APOB-LIPOPROTEINS

血浆胆固醇、低密度脂蛋白和低密度脂蛋白浓度升高 载脂蛋白B被认为是导致糖尿病的危险因素 动脉硬化。血浆中的低密度脂蛋白水平将显著 受低密度脂蛋白受体活性调节，特别是肝脏低密度脂蛋白受体活性 活动。然而，低密度脂蛋白的浓度也受到 极低密度脂蛋白的分泌和转化为低密度脂蛋白。在过去的几年里，它 很明显，过量生产含载脂蛋白B的粒子，而不是 伴随而来的是它们的部分分解代谢率的相应增加 对很大比例的高胆固醇血症患者负责。 因此，拟议的研究将调查载脂蛋白B的调节 人肝癌细胞(Hep G2)的分泌，以及后来在Hep G2培养的 原代人肝细胞。 我的实验室最近完成的一项研究表明，只有一小部分 事实上，Hep G2细胞合成的载脂蛋白B分子中， 其中很大一部分在合成后不久就会迅速降解。此外, 在培养基中添加油酸具有保护作用。 新生的载脂蛋白B来自细胞内的降解。因此，看起来一个 翻译后机制负责确定 肝细胞分泌载脂蛋白B分子。这是公安部的总体 含载脂蛋白B的脂蛋白分泌受调控的假说 通过将载脂蛋白B引导到降解性或分泌性的过程 小路。这将对理解规则具有重要意义 ApoB分泌来更详细地定义这一途径并研究 影响它的因素很多。 因此，这项建议的具体目的是：1)划定职位-- 调节新合成比例的翻译机制 Hep G2细胞分泌的载脂蛋白B。2)确定油酸如何改变 上述降解机制和保护新生载脂蛋白B 细胞内降解。3)确定细胞是否发生变化 胆固醇的可利用性影响载脂蛋白B的降解机制。4) 确定载脂蛋白B分子的哪些结构域参与 Hep G2基因对载脂蛋白B细胞内降解的调节 带有编码被截短的载脂蛋白B分子的DNA的细胞。

Increased concentrations of plasma cholesterol, LDL cholesterol, and LDL apo B have been implicated as risk factors for the development of atherosclerosis. The levels of LDL in plasma will be significantly regulated by LDL receptor activity, especially hepatic LDL receptor activity. However, LDL concentrations are also influenced by the rates of VLDL secretion and conversion to LDL. In the last several years it has become evident, that overproduction of apo B-containing particles, without an accompanying comparable increase in their fractional catabolic rate, is responsible for a large percentage of patients with hypercholesterolemia. Therefore, the proposed studies will investigate the regulation of apo B secretion in human hepatoma cells (Hep G2) and, later, in cultures of primary human hepatocytes. A study recently completed in my laboratory has shown that only a fraction of the apo B molecules synthesized by Hep G2 cells are secreted, in fact, a large proportion are rapidly degraded soon after synthesis. In addition, adding oleic acid to the culture medium had the effect of protecting nascent apo B from intracellular degradation. Thus, it appears that a post-translational mechanism is responsible for determining the number of apo B molecules secreted by the hepatocyte. It is the PI's overall hypothesis that the secretion of apo B-containing lipoproteins is regulated by processes which direct apo B to either the degradative or secretory pathways. It will be important in the understanding of the regulation of apo B secretion to define this pathway in more detail and study what factors affect it. Therefore, the specific aims of this proposal are: 1) Delineate the post- translational mechanism which regulates the proportion of newly synthesized apo B that is secreted by Hep G2 cells. 2) Determine how oleic acid alters the above degradative mechanism and protects nascent apo B from intracellular degradation. 3) Determine whether changes in cellular cholesterol availability affect the apo B degradative mechanism. 4) Determine which domains of the apo B molecule are involved in the regulation of intracellular degradation of apo B by transfecting Hep G2 cells with cDNAs coding for truncated apo B molecules.