Abstract 564: Foxo3a regulates cell cycle arrest through the regulation of p53, p21 and GADD45 signaling activity in Quercetin-treated MDA-MB-231 breast cancer cells.
Authors: Kim Hae-Sung , Nam Ju-Suk , Lee Sang Su , Kim Lee-Su , Ryu Byung-Yoon , Kang Hee-Joon , Choi Byung-Su , Ganbold Bilguun , Ko Yun-Cheol 
Published: August 2014

Abstract
Forkhead box O (FoxO) transcription factors play an important role in multiple signaling pathways and physiological and pathological processes including apoptosis, proliferation metabolism, immunity, and tumorigenesis. Activation of the FoxO subfamily in cells can upregulate cell-cycle inhibitors p21Cip1 and p27Kip1 and downregulate the cell-cycle regulator cyclin D1/2, consequently leading to G1/S arrest of cells.
Recently, quercetin has attracted much attention in relation to its anticancer activities in many cancer models, however, molecular mechanisms underlying quercetin-mediated cellular responses remain poorly defined. We have previously observed that apoptosis of breast cancer cells in response to quercetin was mediated by transcriptional activation of Foxo3a. In addition, C-Jun N-treminal kinase (JNK) regulated the activation of FoxO3a, leading to apoptosis. However, early apoptotic cells stained with Annexin V were not enough to illustrate the whole amount of decreased cell viability as detected by MTT assay.
To clarify this point, we analyzed changes of their cell cycle after stimulation of 20μM quercetin and detected obvious cell cycle arrest at S and G2/M phases leading to delay in their progression. Treatment of quercetin resulted in 3 fold induced population of S phase and 2 fold induced population of G2/M phase, along with 35 % reduced population of G1 phase. Using luciferase reporter assay, MDA-MB231 cells treated with quercetin represented highly increased level of p53, p21 and GADD45 signaling activity, which control cell cycle of breast cancer cells. Moreover, reporter activities of p53, p21 and GADD45 were not stimulated when the expression of Foxo3a was abolished using transfection of Foxo3a shRNA. Since the activation of Foxo3a coincided with increased phosphorylation of JNK after treatment of quercetin, signaling pathways for cell cycle were analyzed in the presence of inhibitor for JNK (SP600125). SP600125 reversed the activation of p53, p21 and GADD45 signaling as well as the activation of Foxo3a. Flow cytometry revealed that quercetin-induced cell cycle arrest of MDA-MB231 cells was partially abrogated when cells were treated with SP600125.Taken together, our data show that cell cycle arrest of breast cancer cells in response to quercetin is dependent upon Foxo3a activation regulated by JNK, resulting in the activation of p53, p21 and GADD45 signaling pathways. These results suggest that an understanding of precise molecular mechanisms for anti-cancer property of quercetin .
Citation Format: Hae-Sung Kim, Ju-Suk Nam, Sang Su Lee, Lee-Su Kim, Byung-Yoon Ryu, Hee-Joon Kang, Byung-Su Choi, Bilguun Ganbold, Yun-Cheol Ko. Foxo3a regulates cell cycle arrest through the regulation of p53, p21 and GADD45 signaling activity in Quercetin-treated MDA-MB-231 breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 564. doi:10.1158/1538-7445.AM2013-564