Identification of the promoter elements involved in the stimulation of ASCT2 expression by glutamine availability in HepG2 cells and the probable involvement of FXR/RXR dimers.

Abstract

Expression of the glutamine transport protein ASCT2 in the human hepatoma cell line HepG2 is increased when cells are cultured in the presence of glutamine and this has been shown to be due to stimulation of the ASCT2 promoter. Analysis of a number of promoter constructs localised the activation site to be between bases -653 and -543. Gel shift assays identified an IR-1 repeat within a 24bp region of this sequence which bound at least two nuclear proteins. Protein binding to this site was significantly higher in cells grown in glutamine-containing medium than when glutamine was absent. The identity of the higher molecular weight species binding to this promoter element was likely to be FXR/RXR dimers. Simultaneous overexpression of FXR and RXR increased the promoter activity in cells grown without glutamine to the same extent as did glutamine addition; the effects of glutamine and FXR/RXR expression were not additive. Mutagenesis of the FXR/RXR binding site in the promoter construct abolished glutamine and FXR/RXR stimulation. Real-time PCR showed levels of FXR mRNA were significantly increased in response to glutamine. The activity of the FXR promoter was also increased in response to glutamine. These results show that the stimulation of ASCT2 expression in response to glutamine in part involves binding of FXR/RXR to the ASCT2 promoter.

• Authors: Claire I Bungard, John D McGivan
• Journal: Archives of biochemistry and biophysics (Arch Biochem Biophys) Vol. 443 Issue 1-2 Pg. 53-9 (Nov 15 2005) ISSN: 0003-9861 [Print] United States
• PMID: 16197915 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Amino Acid Transport System ASC
• DNA-Binding Proteins
• Minor Histocompatibility Antigens
• Receptors, Cytoplasmic and Nuclear
• Retinoid X Receptors
• SLC1A5 protein, human
• Transcription Factors
• farnesoid X-activated receptor
• Glutamine

Topics

• Amino Acid Transport System ASC (chemistry, genetics, metabolism)
• Carcinoma, Hepatocellular (genetics, metabolism)
• Cell Line, Tumor
• DNA-Binding Proteins (metabolism)
• Dimerization
• Gene Expression Regulation, Neoplastic
• Glutamine (metabolism)
• Humans
• Minor Histocompatibility Antigens
• Promoter Regions, Genetic (genetics)
• Receptors, Cytoplasmic and Nuclear
• Retinoid X Receptors (metabolism)
• Transcription Factors (metabolism)