Silencer binding proteins function on multiple cis-elements in the glutathione transferase P gene.

Area of Science:

• Molecular Biology
• Gene Regulation
• Hepatocarcinogenesis Research

Background:

• The glutathione transferase P (GST-P) gene is a specific marker for chemical hepatocarcinogenesis in rats, with its mRNA undetectable in normal liver tissue.
• A DNA fragment located 400 bp upstream of the rat GST-P gene's cap site exhibits negative transcriptional activity.

Purpose of the Study:

• To further characterize the identified DNA fragment's function and mechanism in regulating GST-P gene expression.
• To investigate the nature of the DNA fragment as a potential silencer and identify associated nuclear factors.

Main Methods:

• Functional analysis of the upstream DNA fragment to determine its transcriptional regulatory properties.
• Assessment of the fragment's activity in different orientations and positions relative to the GST-P gene.
• Nuclear factor binding assays and partial purification of a specific binding protein, Silencer Factor A (SF-A).

Main Results:

• The upstream DNA fragment functions as a silencer, independent of orientation and position, suggesting a general role in regulating basal gene expression.
• This silencer is active in various cell lines, including rat, human, and mouse, indicating conserved regulatory mechanisms.
• At least two nuclear factors bind to the silencer, with partially purified Silencer Factor A (SF-A) shown to bind multiple regions within the silencer.

Conclusions:

• The identified DNA fragment acts as a potent silencer for the GST-P gene, playing a crucial role in its negative transcriptional regulation.
• Silencer Factor A (SF-A) is a key protein involved in the silencer's function, highlighting its importance in controlling gene expression.
• The conserved activity across species suggests these silencer elements are general regulators of basal gene expression, relevant beyond hepatocarcinogenesis.