Aryl hydrocarbon Receptor (AhR) Promotes Cell Growth, Induces Stemness Like Characteristics and Metastasis in Ovarian Cancer Cells via Activation of Akt, β‐Catenin and EMT

Abstract

BackgroundOvarian cancer is the most lethal form of all gynecological malignancies with highpitched tumor relapse and chemoresistance. Cancer stem cells (CSCs), a small sub population of cancer cells driving tumor initiation, progression, and metastasis, are known to be a major contributor of therapy resistance. Recent studies have depicted a link between CSC development and exposure to environmental pollutants like 2,3,7,8‐Tetrachlorodibenzo‐p‐dioxin (TCDD). Reports suggest that one of the major pathways that mediate the metabolism of these environmental chemicals is the aryl hydrocarbon receptor (AhR) pathway, whose role in several CSCs is lately demonstrated. However, its role in ovarian cancer development and chemoresistance remains uninvestigated. We hypothesize that AhR and its regulatory genes CYP1A1 and CYP1B1 are involved in the ovarian cancer progression and chemoresistance. The objectives of the present study were a) to examine the role and involvement of AhR in ovarian cancer progression and chemoresistance and b) to explore the underlying mechanisms.MethodsTo test our hypothesis, seven ovarian cancer cell lines; A2780, A2780cis (cisplatin resistant), OVCAR‐3, SKOV‐3, CAOV‐3, and SW‐626 were utilized in this study. Ovarian cancer cells were treated for 24 h with a potent AhR activator, tetrachlorodibenzo‐p‐dioxin (TCDD, 10 nM), thereafter protein expression of AhR, CYP1A1, CYP1B1, pro‐ and anti‐apoptotic, and stemness markers were determined by immunoblotting.Resultsour study showed that SKOV‐3 cells showed highest basal expression of AhR, whereas A2780cis and A2780 expressed the highest basal expression of CYP1A1 and CYP1B1 proteins, respectively. At the inducible levels, treatment of selected cells (OVCAR‐3, SKOV‐3 and A2780) with TCDD significantly induced the protein level of AhR, CYP1A1 in OVCAR‐3 and SKOV‐3, and CYP1B1 in only SKOV‐3 and A2780 cells. To investigate the mechanism involved, we utilized A2780 cells as a model to explore the effect of TCDD on pro‐ and anti‐apototic, Epithelial to Mesenchymal Transition (EMT), and stemness markers. Our results showed that activation of AhR by TCDD in A2780 cells induced phosphorylation of Akt protein with a concomitant increase in the expression of anti‐apoptotic proteins BCL‐2, BCL‐xl and MCL‐1. In addition, a significant increase of aldehyde dehydrogenase (ALDH1), a functional CSC‐specific marker exhibiting important role in cancer progression and chemoresistance was also observed. This effect was also associated with an accumulation of βCatenin, a Wnt transcription factor. Moreover, we found a decrease in E‐cadherin, an epithelial marker, followed by a concurrent increase in Vimentin, a mesenchymal marker, upon AhR activation, confirming the induction of EMT.ConclusionThe results from our study indicate that AhR regulates ovarian cancer progression, exerts stemness characteristics and induces metastasis via activation of Akt, Wnt/β‐Catenin and EMT. This study provides a better understanding of the regulation of ovarian cancer cells in relation to AhR that could help in devising novel therapeutics for better management of ovarian cancer and prevention.