Basic Research
Copyright ©The Author(s) 2005. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Sep 14, 2005; 11(34): 5295-5302
Published online Sep 14, 2005. doi: 10.3748/wjg.v11.i34.5295
Liver-directed gene expression employing synthetic transcriptional control units
Marie-Luise Lemken, Wolfgang A. Wybranietz, Ulrike Schmidt, Florian Graepler, Sorin Armeanu, Michael Bitzer, Ulrich M. Lauer
Marie-Luise Lemken, Wolfgang A. Wybranietz, Ulrike Schmidt, Florian Graepler, Sorin Armeanu, Michael Bitzer, Ulrich M. Lauer, Department of Internal Medicine I, University Clinic Tübingen, D-72076 Tübingen, Germany
Author contributions: All authors contributed equally to the work.
Supported by German Research Foundation (LA 649/11-1); Fortüne-program of the Medical Faculty of the Eberhard-Karls-University Tübingen (F.128101.1); Scholarship from the Pinguin Foundation (Henkel KGaA)
Correspondence to: Ulrich M. Lauer, Department of Internal Medicine I, Medical University Clinic Tübingen, Otfried-Müller-Str. 10, D-72076 Tübingen, Germany. ulrich.lauer@uni-tuebingen.de
Telephone: +49-7071-29-83189 Fax: +49-7071-29-5692
Received: September 29, 2004
Revised: October 23, 2004
Accepted: October 26, 2004
Published online: September 14, 2005
Abstract

AIM: To generate and characterize the synthetic transcriptional control units for transcriptional targeting of the liver, thereby compensating for the lack of specificity of currently available gene therapeutic vector systems.

METHODS: Synthetic transcriptional control unit constructs were generated and analyzed for transcriptional activities in different cell types by FACS quantification, semi-quantitative RT-PCR, and Western blotting.

RESULTS: A new bifunctionally-enhanced green fluorescent protein (EGFP)/neor fusion gene cassette was generated, and could flexibly be used both for transcript quantification and for selection of stable cell clones. Then, numerous synthetic transcriptional control units consisting of a minimal promoter linked to “naturally” derived composite enhancer elements from liver-specific expressed genes or binding sites of liver-specific transcription factors were inserted upstream of this reporter cassette. Following liposome-mediated transfection, EGFP reporter protein quantification by FACS analysis identified constructs encoding multimerized composite elements of the apolipoprotein B100 (ApoB) promoter or the ornithin transcarbamoylase (OTC) enhancer to exhibit maximum transcriptional activities in liver originating cell lines, but only background levels in non-liver originating cell lines. In contrast, constructs encoding only singular binding sites of liver-specific transcription factors, namely hepatocyte nuclear factor (HNF)1, HNF3, HNF4, HNF5, or CAAT/enhancer binding protein (C/EBP) only achieved background levels of EGFP expression. Finally, both semi-quantitative RT-PCR and Western blotting analysis of Hep3B cells demonstrated maximum transcriptional activities for a multimeric 4xApoB cassette construct, which fully complied with the data obtained by initial FACS analysis.

CONCLUSION: Synthetic transcriptional control unit constructs not only exhibit a superb degree of structural compactness, but also provide new means for liver-directed expression of therapeutic genes.

Keywords: Liver gene therapy; Hepatoma gene therapy; Liver-directed gene expression; Synthetic liver-specific promoters