Two proteins essential for apolipoprotein B mRNA editing are expressed from a single gene through alternative splicing
Two proteins essential for apolipoprotein B mRNA editing are expressed from a single gene through alternative splicing
复制标题
DOI：
10.1074/jbc.m111337200
复制
发表时间：
2002-04-12
影响因子：
4.8
通讯作者：
Smith, HC
中科院分区：
文献类型：
--
作者：
Dance, GSC;Sowden, MP;Smith, HC
载脂蛋白 B (apoB) mRNA 编辑涉及胞苷的位点特异性脱氨基作用以形成尿苷，从而产生框内终止密码子。从编辑的 mRNA 翻译的蛋白质与动脉粥样硬化风险降低相关，因此调节肝脏 apoB mRNA 编辑的蛋白质因子受到关注。最近克隆了 apoB mRNA 编辑所必需的人类蛋白质和功能未知的八个氨基酸长变体。我们报道这两种蛋白（以下称为 ACF64 和 ACF65）在 apoB mRNA 的编辑中同等支持 APOBEC-1（编辑体的催化亚基）。它们由 10 号染色体上的单个 82 kb 基因编码。转录物由 15 个外显子编码，这些外显子由最低限度包含在 -0.33 kb DNA 序列中的组织特异性启动子表达。 ACF64 和 ACF65 mRNA 在肝细胞和肠细胞中以大约 1:4 的比例表达。外显子11被选择性剪接以包含或排除外显子12的24个核苷酸，从而分别编码ACF65和ACF64。在外显子 12 中预测了参与选择性 RNA 剪接的富含丝氨酸/精氨酸 (SR) 蛋白 SC35、SRp40、SRp55 和 SF2/ASF 的识别基序。这些 SR 蛋白在肝细胞中的过度表达表明，表达 ACF65 的小基因衍生转录本的选择性剪接被 SRp40 增强了 6 倍。这些数据解释了两种编辑因子的表达，并为它们的不同表达水平提供了可能的解释。
Apolipoprotein B (apoB) mRNA editing involves site-specific deamination of cytidine to form uridine, resulting in the production of an in-frame stop codon. Protein translated from edited mRNA is associated with a reduced risk of atherosclerosis, and hence the protein factors that regulate hepatic apoB mRNA editing are of interest. A human protein essential for apoB mRNA editing and an eight-amino acid-longer variant of no known function have been recently cloned. We report that both proteins, henceforth referred to as ACF64 and ACF65, supported APOBEC-1 (the catalytic subunit of the editosome) equivalently in editing of apoB mRNA. They are encoded by a single 82-kb gene on chromosome 10. The transcripts are encoded by 15 exons that are expressed from a tissue-specific promoter minimally contained within the -0.33-kb DNA sequence. ACF64 and ACF65 mRNAs are expressed in both liver and intestinal cells in an approximate 1:4 ratio. Exon 11 is alternatively spliced to include or exclude 24 nucleotides of exon 12, thereby encoding ACF65 and ACF64, respectively. Recognition motifs for the serine/arginine-rich (SR) proteins SC35, SRp40, SRp55, and SF2/ASF involved in alternative RNA splicing were predicted in exon 12. Overexpression of these SR proteins in liver cells demonstrated that alternative splicing of a mini-gene-derived transcript to express ACF65 was enhanced 6-fold by SRp40. The data account for the expression of two editing factors and provide a possible explanation for their different levels of expression.