Mikkelsen Idun Merete, Huseby Nils-Erik, Visvikis Athanase, Moens Ugo
Department of Medical Biochemistry, Institute of Medical Biology, Faculty of Medicine, University of Tromsø, N-9037 Tromsø, Norway.
Biochem Pharmacol. 2002 Jul 15;64(2):307-15. doi: 10.1016/s0006-2952(02)01116-4.
The single-copy gene for rat gamma-glutamyltransferase (GGT) encodes at least seven distinct mRNAs that differ in their 5'-untranslated regions only. Tissue- and developmental-specific expression of GGT is partly achieved by the presence of many transcription factor-binding sites in the promoters of this gene. In an earlier study we found that GGT mRNAs II and IV levels were increased upon butyrate-induced differentiation of the rat colon carcinoma cell line CC531. The mechanism for this butyrate-induced upregulation remains unknown, but may result from altered promoter activity as butyrate is a known histone deacetylase inhibitor. In the present study, we show by transient transfection studies that butyrate enhanced the expression of the luciferase reporter gene driven by the rat GGT promoter 2 (P2). Trichostatine A (TSA), another histone deacetylase inhibitor, also enhanced transcription from this promoter. The role of the transcription factor site Sp1 in butyrate- or TSA-induced activation of the GGT P2 was examined as Sp1 has been previously shown to play a central role in the transcriptional activation of other genes during butyrate and TSA stimulation. A triple sequence-motif of this isolated Sp1 site linked to a minimal promoter was able to mediate butyrate- and TSA-induced expression of the luciferase reporter gene, while no effect was measured using the minimal promoter alone. Deleting the Sp1 site in the context of the rat GGT P2 strongly reduced the basal transcription activity and abrogated butyrate- and TSA-induced activation of the mutated promoter. These results suggest that butyrate- or TSA-induced activation of the rat GGT P2 can be mediated by a Sp1 binding motif.
大鼠γ-谷氨酰转移酶（GGT）的单拷贝基因编码至少七种仅在5'-非翻译区不同的独特mRNA。GGT在组织和发育过程中的特异性表达部分是通过该基因启动子中存在许多转录因子结合位点来实现的。在早期的一项研究中，我们发现丁酸诱导大鼠结肠癌细胞系CC531分化后，GGT mRNA II和IV的水平升高。这种丁酸诱导的上调机制尚不清楚，但可能是由于丁酸是一种已知的组蛋白脱乙酰酶抑制剂，导致启动子活性改变所致。在本研究中，我们通过瞬时转染研究表明，丁酸增强了由大鼠GGT启动子2（P2）驱动的荧光素酶报告基因的表达。曲古抑菌素A（TSA），另一种组蛋白脱乙酰酶抑制剂，也增强了该启动子的转录。转录因子位点Sp1在丁酸或TSA诱导的GGT P2激活中的作用进行了研究，因为先前已表明Sp1在丁酸和TSA刺激过程中对其他基因的转录激活起着核心作用。与最小启动子相连的这个分离的Sp1位点的三重序列基序能够介导丁酸和TSA诱导的荧光素酶报告基因的表达，而单独使用最小启动子则未检测到效果。在大鼠GGT P2的背景下删除Sp1位点会强烈降低基础转录活性，并消除丁酸和TSA诱导的突变启动子的激活。这些结果表明，丁酸或TSA诱导的大鼠GGT P2激活可由Sp1结合基序介导。
