Nicosia A, Tafi R, Monaci P
IRBM, Istituto di Ricerche di Biologia Molecolare P. Angeletti, Pomezia, Rome, Italy.
Nucleic Acids Res. 1992 Oct 25;20(20):5321-8. doi: 10.1093/nar/20.20.5321.
Liver-enriched factor LFB1 (also named HNF1) is a dimeric transcription activator which is essential for the expression of many hepatocyte-specific genes. Here we demonstrate that LFB1 mutants in the POU A-like or in the homeo domains inhibit wild-type DNA binding by forming inactive heterodimeric complexes. Co-transfection of one of these mutants with wild-type LFB1 in HeLa cells eliminated LFB1 DNA binding and transcriptional activities through a trans-dominant mechanism. Expression of the same dominant negative mutant in human hepatoma HepG2 cells only partially inhibited endogenous LFB1 activity, due to stabilization of LFB1 dimers in these cells. Dimer stabilization in hepatoma cells is mediated by a heat-labile association with an 11kD polypeptide, analogous to the DCoH cofactor identified in rat liver by Mendel et al. (1). The property of stabilizing LFB1 dimers is also shared by HeLa cells which produce a HeLa homolog of DCoH. These results demonstrate that LFB1 dimer stabilization as well as the synthesis of 'stabilizing factors' are not restricted to cells expressing LFB1 or other members of its family.
肝脏富集因子LFB1（也称为HNF1）是一种二聚体转录激活因子，对许多肝细胞特异性基因的表达至关重要。在此我们证明，POU A样结构域或同源结构域中的LFB1突变体通过形成无活性的异二聚体复合物来抑制野生型DNA结合。在HeLa细胞中，将这些突变体之一与野生型LFB1共转染，通过反式显性机制消除了LFB1的DNA结合和转录活性。由于这些细胞中LFB1二聚体的稳定，在人肝癌HepG2细胞中表达相同的显性负性突变体仅部分抑制内源性LFB1活性。肝癌细胞中的二聚体稳定是由与一种11kD多肽的热不稳定结合介导的，类似于Mendel等人在大鼠肝脏中鉴定的DCoH辅因子（1）。产生DCoH的HeLa同源物的HeLa细胞也具有稳定LFB1二聚体的特性。这些结果表明，LFB1二聚体的稳定以及“稳定因子”的合成并不局限于表达LFB1或其家族其他成员的细胞。
