HNF3beta and GATA-4 transactivate the liver-enriched homeobox gene, Hex

Area of Science:

• Molecular Biology
• Gene Regulation
• Hepatology

Background:

• The Hex homeobox gene is expressed in the developing and adult mouse liver.
• Hex expression in the liver coincides with the transcription factor Hepatocyte Nuclear Factor 3beta (HNF3beta).
• The molecular regulators controlling Hex liver expression remain largely unknown.

Purpose of the Study:

• To investigate the role of HNF3beta and GATA-4 transcription factors in driving liver-enriched expression of the Hex gene.
• To identify specific regulatory elements within the Hex promoter responsible for liver-specific activity.

Main Methods:

• Luciferase reporter assays using Hex promoter constructs transfected into liver (HepG2) and non-liver (Cos) cells.
• Co-transfection with expression plasmids for HNF3beta and GATA-4.
• Site-directed mutagenesis of putative transcription factor binding sites.
• Electrophoretic mobility shift assays (EMSA) to confirm protein-DNA interactions.

Main Results:

• The Hex promoter region from -103 to +22 conferred liver-enriched activity.
• HNF3beta and GATA-4 transactivated the Hex promoter through elements within the -103/+22 region.
• Mutation of the HNF3 element significantly reduced promoter activity in HepG2 cells.
• The HNF3 element alone conferred HNF3beta responsiveness to a heterologous promoter.

Conclusions:

• Hepatocyte Nuclear Factor 3beta (HNF3beta) and GATA-4 are key regulators contributing to the liver-enriched expression of the Hex gene.
• Specific response elements for HNF3beta and GATA-4 are located within the proximal Hex promoter region (-103/+22).