The triple threat to nascent apolipoprotein B - Evidence for multiple, distinct degradative pathways
The triple threat to nascent apolipoprotein B - Evidence for multiple, distinct degradative pathways
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DOI：
10.1074/jbc.m008885200
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发表时间：
2001-07-27
影响因子：
4.8
通讯作者：
Williams, KJ
中科院分区：
文献类型：
--
作者：
Fisher, EA;Pan, M;Williams, KJ
我们以前发现，欧米茄-3脂肪酸通过刺激翻译后降解减少培养的肝细胞分泌载脂蛋白B(ApoB)。在这份报告中，我们现在描述这一过程，特别是关于降解新合成的载脂蛋白B的两个已知过程，内质网(ER)相关的降解和细胞表面的重新摄取。首先，我们发现Omega-3诱导的降解优先减少大的、组装的apoB-脂蛋白颗粒的分泌，而apoB多肽长度不是决定因素。其次，基于几种实验方法，不涉及ER相关的降解。第三，重新摄取是已知的唯一破坏完全组装的新生脂蛋白的过程，在原代肝细胞中显然是活跃的，但即使重新摄取被阻止，Omega-3诱导的载脂蛋白B的降解仍在继续。细胞分级分析表明，Omega-3脂肪酸诱导高尔基体apoB(100)显著丢失，而内质网中apoB(100)不明显，这表明内质网是一个后ER过程。为了确定涉及的信号，我们使用了Wortmannin，一种磷脂酰肌醇3-激酶(PI3K)抑制剂，它阻断了Omega-3脂肪酸效应的大部分，如果不是全部的话。因此，新生的载脂蛋白B经历了内质网相关的降解、重新摄取和第三个不同的降解途径，该途径似乎是在大量组装后靶向脂蛋白，并涉及内质网后间隔和PI3K信号。ApoB净分泌的生理学、病理生理学和药理学调节可能涉及这三个降解步骤中的任何一个步骤的改变。
We previously showed that Omega -3 fatty acids reduce secretion of apolipoprotein B (apoB) from cultured hepatocytes by stimulating post-translational degradation. In this report, we now characterize this process, particularly in regard to the two known processes that degrade newly synthesized apoB, endoplasmic reticulum (ER)-associated degradation and re-uptake from the cell surface. First, we found that Omega -3-induced degradation preferentially reduces the secretion of large, assembled apoB-lipoprotein particles, and apoB polypeptide length is not a determinant. Second, based on several experimental approaches, ER-associated degradation is not involved. Third, re-uptake, the only process known to destroy fully assembled nascent lipoproteins, was clearly active in primary hepatocytes, but Omega -3-induced degradation of apoB continued even when re-uptake was blocked. Cell fractionation showed that Omega -3 fatty acids induced a striking loss of apoB(100) from the Golgi, while sparing apoB(100) in the ER, indicating a post-ER process. To determine the signaling involved, we used wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, which blocked most, if not all, of the Omega -3 fatty acid effect. Therefore, nascent apoB is subject to ER-associated degradation, re-uptake, and a third distinct degradative pathway that appears to target lipoproteins after considerable assembly and involves a post-ER compartment and PI3K signaling. Physiologic, pathophysiologic, and pharmacologic regulation of net apoB secretion may involve alterations in any of these three degradative steps.