The Degradation Mechanisms of Aryl Hydrocarbon Receptor in Human Lung Epithelial Carcinoma A549 Cells

Author

Rui Xiong, University of the PacificFollow

Date of Award

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Pharmaceutical and Chemical Sciences

First Advisor

William K. Chan

First Committee Member

Craig Vierra

Second Committee Member

Miki S. Park

Third Committee Member

Wade Russu

Fourth Committee Member

John Livesey

Abstract

The aryl hydrocarbon receptor (AHR), a cytosolic ligand-activated transcription factor, has been acknowledged as a critical regulator of xenobiotic-induced toxicity and carcinogenesis. In the absence of ligand, the AHR is cytoplasmic in a complex with Hsp90, p23, XAP2, and Src. The AHR complex translocates to the nucleus upon ligand binding. After releasing its chaperones, it forms a heterodimer with ARNT, which subsequently binds to a dioxin-responsive element (DRE) for target genes transcription. Multiple aspects of cells are altered by the substantial expression of AHR target genes. Even without the AHR ligand, the cytoplasmic AHR plays a critical role in tumor progression by affecting various cellular functions. Thus, understanding the mechanisms of AHR degradation is crucial, which provides novel ways to control the AHR target genes transcription and cellular functions. In addition to the 26S proteasomal degradation triggered by ligand or geldanamycin treatment, we discovered a novel AHR degradation pathway mediated by autophagy-lysosome in A549 cells. Specifically, the chaperone-mediated autophagy (CMA) facilitates the degradation of basal AHR in the lysosome. It can be activated by 6-AN, resulting in downregulated AHR protein levels and functions, including the ligand-dependent target genes transcription and cell migration/invasion process in A549 cells.p23 as a part of the AHR cytoplasmic complex has been continuously studied in our lab over the past decade. The most prominent role of p23 is protecting AHR from degradation in both immortalized cancer cell lines (mouse hepatoma Hepa1c1c7, human hepatoma Hep3B, human cervical HeLa) and untransformed human lung bronchial/tracheal epithelial (HBTE) cell lines. It encouraged us to investigate the mechanisms further. In A549 cells, downregulation of p23 content reduced AHR protein levels, partially due to an elevated AHR protein degradation. This degradation was not reversed by proteasome inhibitor MG132 but partially restored by lysosome inhibitor CQ. We cannot rule out the possibility that selective macroautophagy was involved in the basal AHR degradation in A549 cells since the PLA results showed a positive interaction between AHR and LC3B. So far, Hela cells could be the best expression system for HaloTag-AHR overexpression. Thus, we can use the HaloTag technology as a powerful tool to study the AHR degradation mechanism via protein labeling and LC-MS/MS analysis.

Pages

154

Recommended Citation

Xiong, Rui. (2023). The Degradation Mechanisms of Aryl Hydrocarbon Receptor in Human Lung Epithelial Carcinoma A549 Cells. University of the Pacific, Dissertation. https://scholarlycommons.pacific.edu/uop_etds/4263