Regulation of AKT1 expression by beta-catenin/Tcf/Lef signaling in colorectal cancer cells
Regulation of AKT1 expression by beta-catenin/Tcf/Lef signaling in colorectal cancer cells
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DOI：
10.1093/carcin/bgi120
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发表时间：
2005-09-01
期刊：
影响因子：
4.7
通讯作者：
Doeberitz, MV
中科院分区：
文献类型：
--
作者：
Dihlmann, S;Kloor, M;Doeberitz, MV
丝氨酸/苏氨酸激酶AKT在控制细胞存活和凋亡之间的平衡中起关键作用。一些报道暗示AKT参与不同人类恶性肿瘤的分子发病机制，并且AKT的过表达最近被证明是结直肠癌发生的早期事件。我们在此报告鉴定了AKT1基因ATG起始位点上游的9个假定的Tcf/左结合元件（TBEs）。其中四个tbe位于转录起始点的上游，而五个tbe位于AKT1基因的外显子1。因此，我们假设AKT1的表达可能受到Wnt/ β -catenin信号的调节。为了阐明AKT在结肠癌细胞中的表达调控，我们在AKT1启动子/增强子衍生的不同区域的控制下，构建了含有荧光素酶基因的报告基因构建体。这些构建体在结直肠癌（CRC）细胞系中的短暂表达导致了报告基因的显著激活。荧光素酶在SW480、SW948和HCT116 CRC细胞中被刺激20- 50倍。相比之下，AKT1启动子/增强子结构在293个胚胎肾细胞中仅表现出弱反应。在结肠癌细胞中共表达具有组成性活性的β -连环蛋白突变体进一步增强了AKT1启动子/增强子的报告基因激活，而通过引入野生型APC或dnTcf-4，该基因被下调。此外，来自结直肠癌患者的肿瘤切片的免疫组织化学染色显示AKT1表达水平升高，与β -连环蛋白的细胞质/细胞核表达增强相关。总之，我们的数据表明β -catenin/Tcf有助于AKT1基因的转录调控。
The serine/threonine kinase AKT plays a critical role in controlling the balance between cell survival and apoptosis. Several reports implicated AKT in the molecular pathogenesis of different human malignancies and overexpression of AKT was recently demonstrated to be an early event in colorectal carcinogenesis. We report here the identification of nine putative Tcf/Lef-binding elements (TBEs) upstream to the ATG initiation site of the AKT1 gene. Four of these TBEs are located upstream of the transcriptional start, whereas five TBEs are situated in Exon 1 of the AKT1 gene. Accordingly, we hypothesized that AKT1 expression might be regulated by Wnt/beta-catenin signaling. To elucidate the regulation of AKT expression in colon cancer cells, we generated reporter constructs containing the luciferase gene under the control of different regions derived from the AKT1 promoter/enhancer. Transient expression of the constructs in colorectal cancer (CRC) cell lines resulted in significant activation of the reporter gene. Luciferase was stimulated 20- to 50-fold in SW480, SW948 and HCT116 CRC cells. In contrast, the AKT1 promoter/enhancer constructs showed only a weak response in 293 embryonic kidney cells. Coexpression of a constitutively active beta-catenin mutant in colon cancer cells further enhanced reporter gene activation from the AKT1 promoter/enhancer, whereas it was downregulated by introduction of either wild-type APC or dnTcf-4. In addition, immunohistochemical staining of tumor sections derived from CRC patients showed elevated expression levels of AKT1, correlating with enhanced cytoplasmic/nuclear expression of beta-catenin. In summary our data suggest that beta-catenin/Tcf contributes to the transcriptional regulation of the AKT1 gene.