人长非编码ACAT1C7基因组结构与表达调控及功能

Acyl-CoA:cholesterol acyltransferase (ACAT) is the exclusive intracellular enzyme that catalyzes the formation of cholesteryl esters (CE) from long-chain fatty acyl coenzyme A and cholesterol, holding pivotal position in cholesterol homeostasis and correlative diseases such as atherosclerosis (AS) and Alzheimer's disease (AD). ACAT localizes in endoplasmic reticulum with very low content, and up to now no natural ACAT enzyme has been purified to homogeneity, so study at the gene level is the essential practical way for revealing its regulatory expression and role. Based on our previous work that have revealed the genomic organization of ACAT1 and ACAT2 genes as well as their regulatory expressions, and our recent results showing that the reported human ACAT1 gene sequence localized in chromosome 7 is a long non-coding ACAT1C7 gene and affects the stability of human ACAT1 mRNA, this application focuses on the special genomic organization and regulatory expression of human long non-coding ACAT1C7 gene as well as the functional affecting of the chromosome 7-produced long non-coding ACAT1C7 RNA on the chromosome 1-produced ACAT1 mRNA decay. These will provide very important bases for further studies on the cellular function of the long non-coding ACAT1C7 gene expression and mechanism of the interchromosomal trans-splicing between the long non-coding ACAT1C7 RNA and the ACAT1 mRNA.

ACAT是细胞内唯一催化游离胆固醇和长链脂肪酸形成胆固醇脂的酶，在胆固醇代谢平衡的生理功能与异常引起AS、AD等病理变化中起重要作用。它定位于内质网膜、含量极低，国际上还未能纯化其天然型酶蛋白，所以通过基因水平研究其功能是目前切实可行途径。本申请项目是在我们前期报道人ACAT1和ACAT2基因组结构、启动子和表达调控等前沿性研究的积累基础上，根据新近研究表明曾报道为人ACAT1基因的7号染色体序列是一个独立的长非编码ACAT1C7基因及其转录RNA可影响ACAT1 mRNA的稳定性等重要线索，集中对长非编码ACAT1C7基因的特异性基因组结构及其与自身表达调控的关系、7号染色体来源长非编码ACAT1C7 RNA 对1号染色体来源ACAT1 mRNA降解的功能作用等进行详细研究，获得成果可为深入阐析长非编码ACAT1C7基因表达的细胞水平功能与跨染色体反式剪接机制等研究奠定极重要的基础。

本项目是在前期前沿研究积累基础上，依据发现人ACAT1 cDNA K1（4011 bp）序列分别来自人1号、7号染色体和7号染色体部分序列是属于长非编码RNA ACAT1C7、且具有快速降解连接的下游1号染色体ACAT1编码序列的调节功能等，进一步探索人长非编码ACAT1C7基因结构功能，同时深入研究人长非编码RNA ACAT1C7调控的ACAT1功能机制。在项目实施研究过程，发现ACAT1活性调控细胞质膜胆固醇水平，在CD8(+) T细胞可发挥重要生理功能和在SK-N-SH神经细胞株可引起病理性变化；发现增强ACAT1表达的肿瘤坏死因子-（TNF-），在人血液中过量可激活单核细胞直接形成泡沫细胞的潜能；揭示人长非编码RNA ACAT1C7基因的不同启动子、顺式元件序列及其功能效应。这些研究成果，不但处于ACAT领域研究前沿，而且促进深入研究ACAT1调控胆固醇代谢平衡及其生理功能、病理变化机制。