Intracellular maturation of apolipoprotein[a] and assembly of lipoprotein[a] in primary baboon hepatocytes.
Intracellular maturation of apolipoprotein[a] and assembly of lipoprotein[a] in primary baboon hepatocytes.
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发表时间：
1993-03
影响因子：
6.5
通讯作者：
Ann L. White;D. Rainwater;R. Lanford
中科院分区：
文献类型：
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作者：
Ann L. White;D. Rainwater;R. Lanford
糖蛋白载脂蛋白[a]（apo[a]）以高度可变的浓度存在于血浆中，并表现为许多遗传决定的大小同种型（400-800 kDa），与低密度脂蛋白中的apoB-100二硫键连接以产生脂蛋白[a]（Lp[a]）。载脂蛋白[a]由肝脏合成，但载脂蛋白[a]和载脂蛋白B的结合位点以及调节其产生的因子尚不清楚。为了检查Lp[a]颗粒的形态发生，用[35 S]半胱氨酸和甲硫氨酸标记表达apo[a]单一低分子量亚型的狒狒肝细胞，并通过免疫沉淀和SDS-PAGE分析apo[a]。稳态标记揭示了细胞内两种分子量形式的载脂蛋白[a]。仅从培养基中回收了大的形式。脉冲追踪研究和内切糖苷酶处理显示，低分子量形式的载脂蛋白[a]代表了在内质网或早期高尔基体隔室中具有延长的停留时间的前体，之后其被加工成成熟形式。一部分成熟形式的载脂蛋白[a]在合成后迅速分泌，而其余部分在后期高尔基体隔室中的停留时间延长。在所有实验中，apoB与apo[a]从培养基中共沉淀，但不从细胞裂解物中沉淀。密度梯度超离心和免疫印迹分析显示，大部分apo[a]以游离形式分泌到培养基中，表明apo[a]和apoB之间的结合发生在分泌后。调节apo[a]在细胞内室之间的运动可能是影响Lp[a]血浆水平的一种机制。
The glycoprotein apolipoprotein[a] (apo[a]) is present in plasma at highly variable concentrations and appears as a number of genetically determined size isoforms (400-800 kDa), disulfide linked to apoB-100 in low density lipoprotein to produce lipoprotein [a](Lp[a]). Apo[a] is synthesized by the liver, but the site of association of apo[a] and apoB and factors that regulate its production are unknown. To examine the morphogenesis of the Lp[a] particle, baboon hepatocytes expressing a single, low molecular weight isoform of apo[a] were labeled with [35S]cysteine and methionine, and apo[a] was analyzed by immunoprecipitation and SDS-PAGE. Steady-state labeling revealed two molecular weight forms of apo[a] inside the cell. Only the large form was recovered from the culture medium. Pulse-chase studies and endoglycosidase treatment revealed that the lower molecular weight form of apo[a] represented a precursor with a prolonged residence time in the endoplasmic reticulum or an early Golgi compartment, after which it was processed to the mature form. A proportion of the mature form of apo[a] was rapidly secreted after synthesis, whereas the remainder had a prolonged residence time in a late Golgi compartment. In all experiments, apoB co-precipitated with apo[a] from the culture medium, but not from cell lysates. Density gradient ultracentrifugation and immunoblot analysis revealed that the majority of apo[a] was secreted into the medium in a free form, suggesting that the association between apo[a] and apoB occurred after secretion. Regulation of the movement of apo[a] between intracellular compartments may be one mechanism by which the plasma levels of Lp[a] are influenced.