Hara E, Yamaguchi T, Nojima H, Ide T, Campisi J, Okayama H, Oda K
Department of Applied Biological Science, Science University of Tokyo, Noda, Japan.
J Biol Chem. 1994 Jan 21;269(3):2139-45.
Three complete cDNA clones encoding Id-related helix-loop-helix (HLH) proteins lacking a basic region were isolated from a pcD2 cDNA expression library prepared from TIG-3 human diploid fibroblasts (HDF). Of these cDNAs (Id-1H, Id-1H', and Id-2H), two (Id-1H and Id-1H') appeared to be derived by alternative RNA splicing. Id-1H and Id-2H seem to be human homologues of mouse Id-1 and Id-2, respectively, and have potential to encode 154 and 135 amino acid proteins. The Id-1H and Id-2H mRNAs were barely detectable in quiescent early passage HDF; serum coordinately induced both mRNAs, with two peaks of expression, in early and late in G1. Antisense oligomers complementary to Id-1H and Id-2H mRNA prevented early passage HDF from entering the S phase of the cell cycle. The treatment of serum-stimulated early passage cells with the antisense Id-1H oligomer completely abolished Id-1H. In senescent cells, serum barely induced the Id-1H and Id-2H mRNAs, although the levels of c-myc expression induced were similar in early passage and senescent cells. The expression levels of these Id genes vary among immortal human cell lines. Both genes were overexpressed in VA4 SV40-transformed lung fibroblasts and EJ-1 bladder carcinoma cells, while these genes were expressed at a very low level in SVts8 cells derived from SV40 tsA-transformed TIG-3 cells. SVts8 cells may acquire some function redundant to Id proteins. HT1080 fibrosarcoma cells expressed the Id-1H gene but not the Id-2H gene, suggesting these Id genes may subserve redundant functions.
从TIG-3人二倍体成纤维细胞（HDF）制备的pcD2 cDNA表达文库中，分离出三个完整的编码缺少碱性区域的Id相关螺旋-环-螺旋（HLH）蛋白的cDNA克隆。在这些cDNA（Id-1H、Id-1H'和Id-2H）中，有两个（Id-1H和Id-1H'）似乎是通过选择性RNA剪接产生的。Id-1H和Id-2H似乎分别是小鼠Id-1和Id-2的人类同源物，有可能编码154和135个氨基酸的蛋白质。在静止的早期传代HDF中几乎检测不到Id-1H和Id-2H mRNA；血清协同诱导这两种mRNA，在G1期早期和晚期出现两个表达峰值。与Id-1H和Id-2H mRNA互补的反义寡聚物阻止早期传代HDF进入细胞周期的S期。用反义Id-1H寡聚物处理血清刺激的早期传代细胞可完全消除Id-1H。在衰老细胞中，血清几乎不诱导Id-1H和Id-2H mRNA，尽管在早期传代细胞和衰老细胞中诱导的c-myc表达水平相似。这些Id基因的表达水平在永生人类细胞系中各不相同。这两个基因在VA4 SV40转化的肺成纤维细胞和EJ-1膀胱癌细胞中均过表达，而在源自SV40 tsA转化的TIG-3细胞的SVts8细胞中表达水平非常低。SVts8细胞可能获得了一些与Id蛋白冗余的功能。HT1080纤维肉瘤细胞表达Id-1H基因但不表达Id-2H基因，表明这些Id基因可能发挥冗余功能。
