Nitsch D, Stewart A F, Boshart M, Mestril R, Weih F, Schütz G
Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg.
Mol Cell Biol. 1990 Jul;10(7):3334-42. doi: 10.1128/mcb.10.7.3334-3342.1990.
The relationship between DNase I-hypersensitive sites (HSs) and transcriptional enhancers of the rat tyrosine aminotransferase (TAT) gene was examined by comparing HSs in and around the TAT gene with the activity of the corresponding DNA sequences in transient transfection assays. In this manner, we identified two HSs as liver-specific enhancers. Of three hepatoma cell lines examined, only one sustained TAT mRNA levels comparable to those of liver. In this cell line, both enhancers were strongly active, and strong hypersensitivity in chromatin over the enhancers was evident. The other two hepatoma cell lines had reduced levels of TAT mRNA and no or altered hypersensitivity over either the enhancers or the promoter. One of these lines carried a negative regulator of the TAT gene, the tissue specific extinguisher Tse-1. This cell line exhibited all HSs characteristic of the strongly active gene except at the promoter; however, one enhancer was inactive even though hypersensitive in chromatin. In a TAT-nonexpressing cell line, inactivity of both enhancers correlated with absence of the respective HSs. We conclude that although hypersensitivity in chromatin necessarily accompanies cell-type-specific enhancer activity, the occurrence of cell-type-specific HSs does not imply that the underlying sequences harbor enhancers active in transient transfection assays.
通过比较大鼠酪氨酸转氨酶（TAT）基因及其周围的脱氧核糖核酸酶I超敏位点（HSs）与瞬时转染实验中相应DNA序列的活性，研究了它们之间的关系。通过这种方式，我们鉴定出两个HSs作为肝脏特异性增强子。在所检测的三种肝癌细胞系中，只有一种细胞系的TAT mRNA水平与肝脏相当。在该细胞系中，两个增强子均具有强烈活性，且增强子区域的染色质呈现出强烈的超敏反应。另外两种肝癌细胞系的TAT mRNA水平降低，增强子或启动子区域无超敏反应或超敏反应改变。其中一个细胞系携带TAT基因的负调控因子，即组织特异性沉默子Tse-1。该细胞系除启动子外，表现出所有强活性基因特有的HSs；然而，一个增强子虽然在染色质中呈现超敏反应，但无活性。在一个不表达TAT的细胞系中，两个增强子均无活性，这与相应HSs的缺失相关。我们得出结论，虽然染色质超敏反应必然伴随着细胞类型特异性增强子活性，但细胞类型特异性HSs的出现并不意味着其潜在序列在瞬时转染实验中具有活性增强子。
