Department of Gene Technology, Tallinn University of Technology, Tallinn, Estonia.
PLoS One. 2011;6(7):e22138. doi: 10.1371/journal.pone.0022138. Epub 2011 Jul 15.
Transcription factor 4 (TCF4 alias ITF2, E2-2, ME2 or SEF2) is a ubiquitous class A basic helix-loop-helix protein that binds to E-box DNA sequences (CANNTG). While involved in the development and functioning of many different cell types, recent studies point to important roles for TCF4 in the nervous system. Specifically, human TCF4 gene is implicated in susceptibility to schizophrenia and TCF4 haploinsufficiency is the cause of the Pitt-Hopkins mental retardation syndrome. However, the structure, expression and coding potential of the human TCF4 gene have not been described in detail.
In the present study we used human tissue samples to characterize human TCF4 gene structure and TCF4 expression at mRNA and protein level. We report that although widely expressed, human TCF4 mRNA expression is particularly high in the brain. We demonstrate that usage of numerous 5' exons of the human TCF4 gene potentially yields in TCF4 protein isoforms with 18 different N-termini. In addition, the diversity of isoforms is increased by alternative splicing of several internal exons. For functional characterization of TCF4 isoforms, we overexpressed individual isoforms in cultured human cells. Our analysis revealed that subcellular distribution of TCF4 isoforms is differentially regulated: Some isoforms contain a bipartite nuclear localization signal and are exclusively nuclear, whereas distribution of other isoforms relies on heterodimerization partners. Furthermore, the ability of different TCF4 isoforms to regulate E-box controlled reporter gene transcription is varied depending on whether one or both of the two TCF4 transcription activation domains are present in the protein. Both TCF4 activation domains are able to activate transcription independently, but act synergistically in combination.
Altogether, in this study we have described the inter-tissue variability of TCF4 expression in human and provided evidence about the functional diversity of the alternative TCF4 protein isoforms.
转录因子 4（TCF4，又名 ITF2、E2-2、ME2 或 SEF2）是一种普遍存在的 A 类碱性螺旋-环-螺旋蛋白，可与 E 盒 DNA 序列（CANNTG）结合。虽然 TCF4 参与了许多不同类型细胞的发育和功能，但最近的研究表明 TCF4 在神经系统中具有重要作用。具体来说，人类 TCF4 基因与精神分裂症易感性有关，TCF4 单倍不足是 Pitt-Hopkins 智力迟钝综合征的原因。然而，人类 TCF4 基因的结构、表达和编码潜力尚未详细描述。
在本研究中，我们使用人类组织样本来描述人类 TCF4 基因的结构和 TCF4 在 mRNA 和蛋白质水平上的表达。我们报告说，尽管广泛表达，但人类 TCF4 mRNA 的表达在大脑中特别高。我们证明，人类 TCF4 基因的许多 5' 外显子的使用可能产生具有 18 个不同 N 末端的 TCF4 蛋白同工型。此外，通过几个内部外显子的选择性剪接，同工型的多样性增加。为了对 TCF4 同工型进行功能表征，我们在培养的人类细胞中过表达了单个同工型。我们的分析表明，TCF4 同工型的亚细胞分布受到差异调节：一些同工型含有二分体核定位信号，仅为核定位，而其他同工型的分布依赖于异二聚体化伴侣。此外，不同 TCF4 同工型调节 E 盒控制的报告基因转录的能力因蛋白中是否存在两个 TCF4 转录激活结构域之一或两者而异。两个 TCF4 激活结构域都可以独立激活转录，但协同作用。
总之，在这项研究中，我们描述了人类 TCF4 表达的组织间变异性，并提供了关于替代 TCF4 蛋白同工型功能多样性的证据。
