Tewari M, Yu M, Ross B, Dean C, Giordano A, Rubin R
Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
Cancer Res. 1997 Sep 15;57(18):4063-9.
Many growth factors and cytokines act as cellular survival factors by preventing programmed cell death (apoptosis). However, the specific genes and corresponding proteins that mediate survival are poorly defined. To identify potential survival genes, a cDNA library was prepared from murine fibroblasts and screened by a functional expression cloning approach. A 1023-bp cDNA, AAC-11, was identified that encodes a protein of approximately 25 kDa. The AAC-11 gene shows strong species conservation and is ubiquitously expressed in embryonic and adult tissues with multiple transcripts, as well as in various human tumor cell lines. The predicted protein contains a leucine zipper domain but lacks a DNA-binding domain. BALB/c3T3 fibroblasts that were stably transfected with AAC-11 cDNA were viable in serum-free medium for up to 12 weeks. The protective action of AAC-11 was abolished by mutation of leucines to arginines within the leucine zipper domain. We also isolated a longer AAC-11 cDNA that codes for up to an additional 290 amino-terminal amino acids but did not protect against apoptosis. The cDNA for human AAC-11 was identified and exhibits strong homology with the murine species and retains the leucine zipper domain. Western immunoblots of BALB/c3T3 cells using rabbit anti-AAC-11 polyclonal serum revealed a major native 55-kDa AAC-11 protein and a minor 25-kDa protein corresponding to the long and short forms of AAC-11 cDNA, respectively. In summary, we report a cDNA whose expression supports cell viability after withdrawal of growth factors. The corresponding native protein may function as a novel inhibitor of apoptosis.
许多生长因子和细胞因子通过防止程序性细胞死亡（凋亡）而充当细胞存活因子。然而，介导存活的具体基因和相应蛋白质却鲜为人知。为了鉴定潜在的存活基因，我们从小鼠成纤维细胞制备了一个cDNA文库，并通过功能表达克隆方法进行筛选。我们鉴定出一个1023bp的cDNA，即AAC - 11，它编码一种约25kDa的蛋白质。AAC - 11基因显示出很强的物种保守性，在胚胎和成年组织中以多种转录本普遍表达，在各种人类肿瘤细胞系中也有表达。预测的蛋白质含有一个亮氨酸拉链结构域，但缺乏DNA结合结构域。稳定转染了AAC - 11 cDNA的BALB/c3T3成纤维细胞在无血清培养基中可存活长达12周。亮氨酸拉链结构域内的亮氨酸突变为精氨酸后，AAC - 11的保护作用消失。我们还分离出一个更长的AAC - 11 cDNA，它编码另外多达290个氨基末端氨基酸，但不能防止细胞凋亡。已鉴定出人类AAC - 11的cDNA，它与小鼠物种具有很强的同源性，并保留了亮氨酸拉链结构域。用兔抗AAC - 11多克隆血清对BALB/c3T3细胞进行Western免疫印迹分析，结果显示主要的天然5五十五kDa AAC - 11蛋白和次要的25kDa蛋白，分别对应于AAC - 11 cDNA的长形式和短形式。总之，我们报告了一个cDNA，其表达在生长因子撤除后支持细胞存活。相应的天然蛋白质可能作为一种新型的凋亡抑制剂发挥作用。
