Accumulation of distinct prelamin A variants in human diploid fibroblasts differentially affects cell homeostasis
Accumulation of distinct prelamin A variants in human diploid fibroblasts differentially affects cell homeostasis
复制标题
DOI：
10.1016/j.yexcr.2010.10.014
复制
发表时间：
2011-02-01
影响因子：
3.7
通讯作者：
Comai, Lucio
中科院分区：
文献类型：
--
作者：
Candelario, Jose;Borrego, Stacey;Comai, Lucio
核纤层蛋白A是核纤层的组分，其在核的结构组织和功能中起主要作用。核纤层蛋白A作为前核纤层蛋白A前体合成，其经历四个连续的翻译后修饰以产生成熟核纤层蛋白A。值得注意的是，LMNA基因中的大量点突变导致一系列不同的人类疾病，统称为核纤层蛋白病。核纤层蛋白A的突变影响细胞功能和引起疾病的机制尚不清楚。有趣的是，最近的研究表明，正常核纤层蛋白A通路的改变可能导致细胞功能障碍。具体而言，我们和其他人已经表明，在细胞水平上，在没有突变或改变剪接事件的情况下，野生型前核纤层蛋白A的表达增加导致生长缺陷表型，其类似于表达核纤层蛋白A的突变形式的细胞，称为早老蛋白，与Hutchinson-Gilford早衰综合征（HGPS）相关。值得注意的是，表达升高水平的野生型前层蛋白A的细胞的表型可以通过用法尼基转移酶抑制剂处理或过表达ZMPSTE 24（一种关键的前层蛋白A加工酶）来逆转，这表明一种或多种前层蛋白A中间体的稳态水平的微小增加足以诱导细胞毒性。在这里，研究核纤层蛋白A途径毒性的分子基础，我们的特点是发生在细胞表达不同的前核纤层蛋白A变体模仿特定的前核纤层蛋白A加工中间体的表型变化。该分析表明，不同的前核纤层蛋白A变体差异影响细胞生长，核膜形态，核纤层蛋白A的核分布和转录的基本过程。组成型法尼基化的前核纤层蛋白A变体的表达诱导核纤层蛋白A聚集体的形成和核膜形态的显著变化，这导致基础转录因子TATA结合蛋白（TBP）和全局转录水平降低，并严重限制细胞生长。不能被法尼基化的前核纤层蛋白A变体的表达，虽然没有明显影响细胞生长，但导致核纤层蛋白A核质灶的形成，并导致在一个较小的细胞亚群中，伴随着TBP和转录水平降低的核形态变化。相反，成熟核纤层蛋白A的表达不影响任何这些参数。这些数据表明，任何部分加工的前核纤层蛋白A蛋白的积累在一定程度上改变了细胞内稳态，即使最显著的影响是由具有永久法尼基化羧基末端尾部的变体引起的。(C)2010年爱思唯尔公司All rights reserved.
Lamin A is a component of the nuclear lamina that plays a major role in the structural organization and function of the nucleus. Lamin A is synthesized as a prelamin A precursor which undergoes four sequential post-translational modifications to generate mature lamin A. Significantly, a large number of point mutations in the LMNA gene cause a range of distinct human disorders collectively known as laminopathies. The mechanisms by which mutations in lamin A affect cell function and cause disease are unclear. Interestingly, recent studies have suggested that alterations in the normal lamin A pathway can contribute to cellular dysfunction. Specifically, we and others have shown, at the cellular level, that in the absence of mutations or altered splicing events, increased expression of wild-type prelamin A results in a growth defective phenotype that resembles that of cells expressing the mutant form of lamin A, termed progerin, associated with Hutchinson-Gilford Progeria syndrome (HGPS). Remarkably, the phenotypes of cells expressing elevated levels of wild-type prelamin A can be reversed by either treatment with farnesyltransferase inhibitors or overexpression of ZMPSTE24, a critical prelamin A processing enzyme, suggesting that minor increases in the steady-state levels of one or more prelamin A intermediates is sufficient to induce cellular toxicity. Here, to investigate the molecular basis of the lamin A pathway toxicity, we characterized the phenotypic changes occurring in cells expressing distinct prelamin A variants mimicking specific prelamin A processing intermediates. This analysis demonstrates that distinct prelamin A variants differentially affect cell growth, nuclear membrane morphology, nuclear distribution of lamin A and the fundamental process of transcription. Expression of prelamin A variants that are constitutively farnesylated induced the formation of lamin A aggregates and dramatic changes in nuclear membrane morphology, which led to reduced levels of the basal transcription factor TATA-binding protein (TBP) and global transcription, and severely limited cell growth. Expression of a prelamin A variant that cannot be farnesylated, although did not appreciably influence cell growth, resulted in the formation of lamin A nucleoplasmic foci and caused, in a minor subpopulation of cells, changes in nuclear morphology that were accompanied by reduced levels of TBP and transcription. In contrast, expression of mature lamin A did not affect any of these parameters. These data demonstrate that accumulation of any partially processed prelamin A protein alters cellular homeostasis to some degree, even though the most dramatic effects are caused by variants with a permanently farnesylated carboxyl-terminal tail. (C) 2010 Elsevier Inc. All rights reserved.