Abstract B45: Carnosic acid from rosemary induces degradation of androgen receptor and is critically regulated by the ER stress protein CHOP
Authors: Petiwala Sakina M. , Li Gongbo , Johnson Jeremy J. 
Published: January 2014

Background: The rosemary plant is well known for its diverse collection of dietary polyphenols that possess a variety of biological properties that may be beneficial to a variety of applications including preventing and/or delaying cancer. Previously, we have reported that carnosol, a dietary diterpene from rosemary (Rosmarinus officinialis), is a dual disruptor of androgen and estrogen receptor alpha. In our most recent study evaluating diterpenes from rosemary for anti-cancer activity we have identified carnosic acid as a disruptor of androgen receptor activity.

Materials and Methods: Experiments were performed using prostate epithelial cells, LNCaP, and 22Rv1 cells. Cell viability and cell proliferation studies were performing using MTT and BrdU assays respectively. Using siRNA and chemicals inhibitors of endoplasmic reticulum (ER) stress we evaluated the relationship between ER stress and carnosic acid induced degradation of the androgen receptor using Western blotting, ELISA, and fluorescence microscopy.

Results: Carnosic acid was observed to decrease cell viability of LNCaP and 22Rv1 cells in a dose dependent manner. The decreased viability was associated with apoptosis as evidenced by a significant increase in cleaved caspase 3 protein. Carnosic acid was found to modulate several proteins involved with ER stress including the ER stress chaperone protein (BiP) and proteins associated directly with ER stress (IRE1 and CHOP). A dose dependent decrease in the expression of AR in 22Rv1 and LNCap cells was observed following carnosic acid treatment. Interestingly, when the ER stress protein CHOP was inhibited either chemically or by siRNA carnosic acid was unable to decrease the protein expression of AR. The proteasome has been shown to be regulated by multiple proteins including proteins associated with ER stress. The degradation of androgen receptor was inhibited when cells were co-treated with the proteasome inhibitor MG-132 and carnosic acid suggesting that decrease in AR expression was due to proteasomal degradation. Interestingly, the induction of CHOP following carnosic acid treatment in LNCaP and 22Rv1 cells was not observed in prostate epithelial cells.

Conclusion: Carnosic acid induces the expression of CHOP which was found to regulate degradation of androgen receptor. Interestingly, the degree of degradation appears to be greater in LNCaP cells compared to 22Rv1 cells suggesting there may be a differential response in AR degradation dependent on the type of AR mutation (e.g. T877 or duplicate exon2), however, further work is needed. Furthermore, we evaluated prostate epithelial cells and observed a decrease in ER stress suggesting a differential response and possibly even a protective role. Our data suggests that these natural diterpenes possess strong anticancer activity and should be evaluated further as potential chemopreventive and/or chemotherapeutic agents for controlling prostate cancer.

Citation Format: Sakina M. Petiwala, Gongbo Li, Jeremy J. Johnson. Carnosic acid from rosemary induces degradation of androgen receptor and is critically regulated by the ER stress protein CHOP. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B45.