Schafer A J, Fournier R E
Department of Molecular Medicine, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
Somat Cell Mol Genet. 1992 Nov;18(6):571-81. doi: 10.1007/BF01232653.
The phosphoenolpyruvate carboxykinase (PEPCK) gene is highly expressed in cultured rat hepatoma cells, but extinguished in hepatoma x fibroblast hybrids. Extinction of PEPCK gene expression in hybrids is a polygenic process that involves several fibroblast loci, only one of which (tissue-specific extinguisher-1, TSE1) has been characterized to date. To identify sequence elements of the PEPCK gene that are involved both in TSE1-mediated extinction and in TSE1-independent processes, we assayed expression of chimeric PEPCK transgenes in transiently and stably transfected hybrid cells. We report that TSE1 responsiveness mapped to the PEPCK CRE (cAMP response element), as shown previously for the tyrosine aminotransferase gene. This was expected from the recent identification of the TSE1 gene product as a regulatory subunit of protein kinase A. However, none of the transgenes we assayed were responsive to TSE1-independent extinction mechanisms, suggesting that these controls require DNA sequences and/or chromatin structures that were not present in the transfected reporters. The implications of these findings are discussed.
磷酸烯醇式丙酮酸羧激酶（PEPCK）基因在培养的大鼠肝癌细胞中高度表达，但在肝癌细胞与成纤维细胞的杂交细胞中则不表达。杂交细胞中PEPCK基因表达的沉默是一个多基因过程，涉及几个成纤维细胞基因座，到目前为止，其中只有一个（组织特异性沉默子-1，TSE1）得到了表征。为了鉴定PEPCK基因中既参与TSE1介导的基因沉默又参与不依赖TSE1的过程的序列元件，我们检测了嵌合PEPCK转基因在瞬时和稳定转染的杂交细胞中的表达。我们报告，TSE1反应性定位于PEPCK CRE（cAMP反应元件），正如先前酪氨酸转氨酶基因的情况一样。鉴于最近鉴定出TSE1基因产物是蛋白激酶A的调节亚基，这是可以预期的。然而，我们检测的转基因中没有一个对不依赖TSE1的沉默机制有反应，这表明这些调控需要转染的报告基因中不存在的DNA序列和/或染色质结构。本文讨论了这些发现的意义。
