Characterization of the human ABL promoter regions

Gel retardation and DNAase 1 footprinting experiments have been performed to characterize the promoter sequences of exon 1a and 1b of the human ABL gene. Several Sp1 motifs and CCAAT boxes are found to be protected by nuclear proteins in the 1b promoter but none of the 7 reported Sp1 sites in 1a were found to bind protein. Multiple sets of initiation sites seem to exist in the 1b promoter region which may represent individual initiation sites, distributed over a DNA region of up to 700 bp. Starting with the most distal initiation site, 1a and 1b ABL promoter sequences show a high degree of homology, suggesting that one is derived from the other. However, multiple evolutionary changes in the 1a promoter sequence indicate that type 1a ABL expression may be differently regulated than 1b.     

正常人及视网膜母细胞瘤患者Rb基因启动子结构、功能和突变的研究

目的检测正常人及视网膜母细胞瘤（ＲＢ）患者Ｒｂ基因５′端调控区的ＤＮＡ序列,以及不同的ＤＮＡ片段的转录调控活性,研究Ｒｂ基因启动子的结构、功能以及突变对功能的影响和与ＲＢ发病的关系。方法应用ＳＳＣＰ分析及ＤＮＡ序列测定检测正常人及ＲＢ患者Ｒｂ基因启动子的ＤＮＡ序列和点突变;分离Ｒｂ基因５′端不同位置及不同大小的ＤＮＡ片段,通过氯霉素乙酰基转移酶做报告基因,检测不同的ＤＮＡ片段的转录调控活性。结果Ｒｂ基因产物起始密码上游３２７ｂｐ至８７ｂｐ间２４０ｂｐ的ＤＮＡ片段具有基本的启动子功能,其上游和下游的ＤＮＡ序列内可能还存在正或负转录调控元件。１００例正常人Ｒｂ基因启动子ＤＮＡ序列未见有任何变异,但３０２例ＲＢ患者中５例有点突变并伴有ＣＡＴ活性明显降低。结论Ｒｂ基因启动子的ＤＮＡ序列非常稳定,其突变常常导致启动子活性下降,并与视网膜母细胞瘤的遗传易感性有关     

食管癌细胞Ezrin基因转录调控区克隆及其启动子活性的鉴定

目的:克隆食管癌侵袭转移相关基因Ezrin的转录调控区序列,进行启动子活性鉴定及初步的生物信息学分析。方法:利用在线程序对Ezrin基因可能的转录调控区进行GC含量和CpG岛分析以及转录因子结合位点预测;采用PCR法从食管癌细胞基因组DNA中克隆Ezrin基因-1759/ 134和-726/ 134区段,构建萤火虫荧光素酶报告基因表达质粒pGLB-hE(-1759/ 134)和pGLB-hE(-726/ 134),检测所克隆片段的启动子活性。结果:Ezrin基因5′侧翼区为高GC含量区,存在CpG岛,无典型的TATA盒,然而转录因子Sp1结合位点却无处不在。与对照质粒pGLB相比,重组质粒pGLB-hE(-726/ 134)具有较强的荧光素酶活性,pGLB-hE(-1759/ 134)的荧光素酶活性约是pGLB-hE(-726/ 134)的2倍。结论:Ezrin基因的-726/ 134区段具有启动子活性,含有Ezrin基因的核心启动子区和调节性启动子区;-1759/-726区段具有增强启动子活性的作用,含有Ezrin基因增强子元件区。     

Characterization of the human N-ras promoter region

Overexpression of ras proto-oncogenes has been implicated in cancer development. We therefore initiated a study of the human N-ras promoter to determine the regions that control N-ras expression and their potential for interaction with DNA-binding proteins. N-ras CAT constructs were stably integrated into K562 cells by electric field-mediated gene transfer in order to determine functional regions within the human N-ras promoter. A significant proportion of promoter activity was found to lie within a 439 bp fragment comprising an untranslated exon (exon 1) with the adjacent 5' sequence and a small CpG island. A 109 bp [corrected] fragment at the 5' end of exon 1 was essential for promoter activity, while a 45 bp [corrected] deletion from within this region decreased promoter activity by two-thirds. Unlike the human H-ras and mouse K-ras promoters, the N-ras promoter did not exhibit bidirectional activity. DNAse footprinting of the 439 bp fragment revealed seven protected regions, many of which contain sequences homologous to known DNA-binding protein sites (MLTF/myc, CREB/ATF, AP-1, AP-2, myb and E4TF1). In contrast, four putative Sp1 sites did not footprint. Using purified MLTF and appropriate competitors in gel shift and DNAase footprinting assays, we demonstrated binding of MLTF to the MLTF consensus sequence within exon 1.     

A negative regulatory element within the proximal promoter region of the rat ornithine decarboxylase gene

A putative Ets site with a core of GGAA located at nt -88 to -85 of the rat ornithine decarboxylase (ODC) gene was characterized by site-directed mutagenesis and transient expression assays. Mutation of this site, when in pODClux2m, which contains a cluster of four Sp1-binding sites, resulted in a 2.6-fold increase in basal promoter activity in untreated cells, whereas the ratio of activity in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated cells relative to the ratio in untreated cells (the induction ratio) remained largely unchanged. However, when the mutation was in pODClux168, which contains only a single Sp1-binding site (GC box V), it caused little alteration to either basal promoter activity or TPA induction ratio. A protein of 55-60 kDa was found specifically bound to this site, as shown by ultraviolet cross-linking assay. In competition assay and methylation interference assay, this protein was shown to occupy the GGAA core, although it showed no antigenic relation to c-Ets-1 in an supershift assay. We suggest that this protein binds specifically to the GGAA core and functions to inhibit activation of the ODC promoter by distal elements, including the upstream Sp1 sites.