p23 Modulates Aryl Hydrocarbon Receptor Protein Levels in Normal Cell Lines
Poster Number
8a
Introduction/Abstract
Aryl hydrocarbon receptor (AHR) is a transcription factor activated in response to exposure of environmental toxins. Unliganded AHR resides in the cytosol of the cell bound to its chaperone protein complex contains two molecules of Hsp90, XAP2 and p23. Upon ligand binding, the receptor translocates to the nucleus and heterodimerizes with AHR nuclear translocator (ARNT) to activate its target genes expression. The effects of AHR activation have been primarily associated with numerous human diseases, especially cancers. As AHR is highly expressed in a panel of tumors, molecules that modulate AHR expression or antagonize aberrant AHR activity could be considered as potential candidates for the treatment of cancer.
Purpose
p23, a co-chaperone of AHR, was found to be capable of regulating ligand-dependent AHR activation and functions. Previous study from our laboratory showed that low expression of the p23 protein is associated with poor AHR protein stability and function in cancer cell lines. While in a p23 null mouse model, it was reported that p23 did not affect the AHR expression. To better understand this apparent dichotomy, we explored the possibility that the AHR expression may be regulated differently in cancer cells than in normal cells.
Method
We analyzed the AHR protein levels by immunoblotting assays in three normal cell lines with either wild-type or reduced p23 protein levels, namely human breast epithelial cells (MCF-10A), human bronchial tracheal epithelial cells (HBTEC), and mouse type I regulatory T cells (Tr1). AHR function in WT or p23KD HBTECs was tested by CYP1A1-dependent EROD assay and ROS production, which were induced by cigarette smoke condensate (CSC) and benzo[a]pyrene (BaP).
Results
We observed that the AHR expression was significantly reduced by about 38-57% compared to the controls after 72 hours transfection of p23-specific shRNA in all three normal cells, indicating that p23 is more important for the control of AHR expression in normal conditions than previously expected. EROD assay showed that CSC or BaP induced, AHR-mediated CYP1A1 activity was reduced in p23KD HBTECs. Oxidative stress assay from Muse cell analyzer showed that 8-hour treatment of CSC and BaP caused a increase of ROS amount in HBTECs, while the production of ROS was suppressed in p23KD cells.
Significance
Collectively, these results suggest that down-regulation of p23 caused reduction of the AHR protein levels in normal cell lines (i.e. breast, immune, and bronchial/tracheal cells). AHR function is also altered by knockdown of p23. Particularly, our study provides the evidence that knockdown of p23 protects human lung cells from the AHR-mediated toxicities upon cigarette smoking.
Location
DeRosa University Center
Format
Poster Presentation
Poster Session
Morning 10am-12pm
p23 Modulates Aryl Hydrocarbon Receptor Protein Levels in Normal Cell Lines
DeRosa University Center
Aryl hydrocarbon receptor (AHR) is a transcription factor activated in response to exposure of environmental toxins. Unliganded AHR resides in the cytosol of the cell bound to its chaperone protein complex contains two molecules of Hsp90, XAP2 and p23. Upon ligand binding, the receptor translocates to the nucleus and heterodimerizes with AHR nuclear translocator (ARNT) to activate its target genes expression. The effects of AHR activation have been primarily associated with numerous human diseases, especially cancers. As AHR is highly expressed in a panel of tumors, molecules that modulate AHR expression or antagonize aberrant AHR activity could be considered as potential candidates for the treatment of cancer.
