Estrogen‐Inducible Derivatives of Hepatocyte Nuclear Factor‐4, Hepatocyte Nuclear Factor‐3 and Liver Factor B1 are Differently Affected by Pure and Partial Antiestrogens

Abstract

The tissue-specific transcription factors of the hepatocyte nuclear factor-4 (HNF4), hepatocyte nuclear factor-3 (HNF3), and liver factor B1 (LFB1) families are thought to play a role in the development of internal organs and in the tissue-specific expression of many distinct genes. We have now constructed derivatives of these proteins by introducing the hormone-binding domain of the estrogen receptor and show that in transient transfections these chimeric proteins act as estrogeninducible transcription factors with the DNA sequence specificity of the original factors. These chimeric transcription factors are differently affected by the partial estrogen antagonist 4-hydroxytamoxifen and the pure antiestrogen N-n-butyl-ll-(3,17-dihydroxy-estra-l,3,5(1O)-trien-7a-yl)Nmethyl-undecamide (ICI 164384) ; 4-hydroxytamoxifen activates, at least partially, all the chimeric factors and the estrogen receptor, while ICI 164384 surprisingly activates the transcription factors derived from HNF3 and LFBl and inhibits only the estrogen receptor and the HNF4 derivative. Together with the DNA-sequence-binding specificity, the different response to estrogen and antiestrogens makes our estrogen receptor fusion proteins useful tools for the investigation of the roles of HNF4, HNF3 and LFBl in gene expression, differentiation and developmental processes.Over the last decade, the investigation of the mechanisms involved in liver-specific gene expression has led to the identification first of DNA elements responsible for this tissue specificity and subsequently of protein factors which are able to bind specifically to these promoter elements. Many of these factors have recently been cloned and shown to be transcriptional activators of reporter genes containing DNA elements that mediate liver-specific gene expression (Lai and Darnell, 1991;Sladek and Darnell, 1992;Xanthopoulos and Mirkovitch, 1993). According to their DNA-binding specificity, these transcription factors were subdivided into the liver factor B 1 (LFBl), hepatocyte nuclear factor-3 (HNF3), hepatocyte nuclear factor-4 (HNF4), or CCAAT bodenhancerbinding protein (CEBP) families (Xanthopoulos and Mirkovitch, 1993). Using the cloned cDNA and antibodies, it was established that these factors are not restricted to the liver but are also found in other tissues Bartkowski et al., 1993). One approach to understand the role of these tissue-specific transcription factors within a certain cell type and in differentiation and embryogenesis is to introduce these factors into cells in which they are normally not expressed. As it has been shown that estrogen- N-n-butyl-ll-(3,17-dihydroxy-estra-l,3,5(10)-trien-7a-yl)N-methyl-undecamide; LFB1, liver factor B1; VP, viral protein.inducible fusion proteins of transcription factors containing the hormone-binding domain of the estrogen receptor are useful tools to investigate the role of transcription factors in these processes (Umek et al., 1991 ;Burk and Klempnauer, 1991 ;Briegel et al., 1993), we decided to establish estrogendependent deriva...

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