Rundlöf Anna-Klara, Janard Magnus, Miranda-Vizuete Antonio, Arnér Elias S J
Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden.
Free Radic Biol Med. 2004 Mar 1;36(5):641-56. doi: 10.1016/j.freeradbiomed.2003.12.004.
Human thioredoxin reductase 1 (TrxR1, the TXNRD1 gene product) is a ubiquitously expressed selenoprotein with many important redox regulatory functions. In this study, we have further characterized the recently identified core promoter region of TXNRD1. One critical Sp1/Sp3 site was found to be important in A549 and HeLa cells, whereas another Sp1/Sp3 site and one Oct1 site bound transcription factors but were, nonetheless, dispensable for transcription. We also experimentally identified several 5'-region TXNRD1 transcript variants using 5'-RACE with cDNA derived from different tissues, and we analyzed all available TXNRD1-derived EST sequences. The results show that the core promoter governs transcription of the clear majority of TXNRD1 transcripts but also that alternative promoters may be activated under rare conditions or in specific cell types. Furthermore, extensive alternative splicing occured in the 5' region of TXNRD1. In total, 21 different transcripts were identified, potentially encoding five isoforms of TrxR1 carrying alternative N-terminal domains. One isoform encompassed a glutaredoxin domain, whereas another encoded a predicted mitochondrial localization signal. These results reveal that the human thioredoxin system is intriguingly complex. Cell-specific transcription of the TXNRD1 gene encoding different isoforms of TrxR1 must be taken into account to fully understand the functions of the human thioredoxin system.
人硫氧还蛋白还原酶1（TrxR1，TXNRD1基因产物）是一种广泛表达的硒蛋白，具有许多重要的氧化还原调节功能。在本研究中，我们进一步对最近鉴定出的TXNRD1核心启动子区域进行了特征分析。发现一个关键的Sp1/Sp3位点在A549和HeLa细胞中很重要，而另一个Sp1/Sp3位点和一个Oct1位点能结合转录因子，但对转录而言却是可有可无的。我们还通过5'-RACE实验鉴定了来自不同组织的cDNA的几个5'-区域TXNRD1转录变体，并分析了所有可用的TXNRD1来源的EST序列。结果表明，核心启动子控制着绝大多数TXNRD1转录本的转录，但在罕见条件下或特定细胞类型中，替代启动子也可能被激活。此外，TXNRD1的5'区域发生了广泛的可变剪接。总共鉴定出21种不同的转录本，可能编码携带不同N端结构域的TrxR1的五种异构体。一种异构体包含一个谷氧还蛋白结构域，而另一种则编码一个预测的线粒体定位信号。这些结果表明，人硫氧还蛋白系统极其复杂。要全面了解人硫氧还蛋白系统的功能，必须考虑编码TrxR1不同异构体的TXNRD1基因的细胞特异性转录。
