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Evidence for two functionally distinct forms of the human Ah receptor
1Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47907, USA.
Journal of Biochemical Toxicology
|April 1, 1995
Summary
The aryl hydrocarbon receptor (AhR) exists in two forms (104 and 106 kDa) in human cells. Only the larger AhR form translocates to the nucleus, indicating distinct functional roles for these AhR variants.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- The aryl hydrocarbon receptor (AhR) is a crucial transcription factor involved in various cellular processes.
- Understanding the different forms and localization of AhR is essential for deciphering its regulatory mechanisms.
Purpose of the Study:
- To investigate the distinct forms of the AhR present in human cell lines.
- To determine the cellular localization and potential functional differences between AhR isoforms.
Main Methods:
- Western blotting using a monoclonal antibody to detect AhR.
- Photoaffinity labeling with a dioxin analog to identify ligand-binding forms.
- SDS-PAGE, sucrose density gradient analysis, and cyanogen bromide fragmentation to characterize AhR forms.
- Analysis of both cytosolic and nuclear fractions.
Main Results:
- Two distinct AhR bands (104 kDa and 106 kDa) were detected in human cell lines.
- Photoaffinity labeling revealed that only the 106 kDa AhR form binds the dioxin analog.
- The 106 kDa AhR form was exclusively found in the nuclear fraction, while both forms were present in the cytosol.
- Proteolytic degradation or N-terminal differences do not explain the existence of the two AhR forms.
Conclusions:
- Human cell lines express two distinct forms of the AhR.
- The 106 kDa AhR is the ligand-binding and nuclear-translocating form.
- The 104 kDa AhR form may have a separate, non-ligand-dependent function or represent a precursor/isoform.