Subcellular localization of FOXO3a as a potential biomarker of response to combined treatment with inhibitors of PI3K and autophagy in PIK3CA-mutant cancer cells
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Hyun-Jung Kim1,2,*, Soo Yoon Lee3,4,*, Chan Young Kim1,2, Yun Hwan Kim1,2, Woong Ju1,2, Seung Cheol Kim1,2
1Innovative Research Center for Control and Prevention of Women’s Cancer, Ewha Womans University Mokdong Hospital, Seoul, Korea
2Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Ewha Womans University Mokdong Hospital, School of Medicine, Ewha Womans University, Seoul, Korea
3Department of Obstetrics and Gynecology, Hanmaeum Changwon Hospital, Changwon, Kyungnam, Korea
4Department of Obstetrics and Gynecology, The Graduate School, School of Medicine, Ewha Womans University, Seoul, Korea
*These authors have contributed equally to this work
Seung Cheol Kim, email: email@example.com
Keywords: PI3K inhibitor, PIK3CA mutant cervical cancer, autophagy inhibitor, FOXO3A, 14-3-3
Abbreviations: PI3K, phosphoinositide-3-kinase; PIK3CA, phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit; HCQ, hydroxychloroquine; FOXO, forkhead box O.
Received: July 28, 2016 Accepted: December 01, 2016 Published: December 27, 2016
Autophagy is the process of lysosome-mediated degradation and recycling that functions as an adaptive survival mechanism during anti-cancer therapy. Aberrant activation of the phosphoinositide-3-kinase (PI3K) pathway frequently occurs in solid tumors, including cervical cancer. However, single-agent PI3K inhibitors show modest anti-tumor efficacy in clinics. To see whether autophagy inhibition improves the efficacy of PI3K inhibitor in PIK3CA-mutant cancer cells, cells were treated with BKM120, a pan-PI3K inhibitor, and the autophagy inhibitor hydroxychloroquine (HCQ). Autophagy inhibition augmented the efficacy of BKM120 depending on PIK3CA-mutant cancer cell type. BKM120 treatment led to the nuclear accumulation of forkhead box O3 (FOXO3a) in Caski and T47D cells, which showed a synergistic effect of BKM120 and HCQ and the strong induction of autophagy. However, most FOXO3a remained in cytoplasm in C33A and ME180 cells, which did not exhibit synergy. These data suggest that BKM120-induced nuclear translocation of FOXO3a might elicit autophagy and be a critical factor determining the synergistic activity of BKM120 and HCQ in PIK3CA-mutant cancer cells. The release of FOXO3a from 14-3-3 by BV02 or 14-3-3 knockdown induced autophagy by BKM120 in C33A cells and sensitized the cells to the combined BKM120 and HCQ treatment, suggesting that cytoplasmic retention of FOXO3a by 14-3-3 even in the presence of BKM120 inhibit autophagy induction and synergistic effect of BKM120 and HCQ combination. Taken together, our study shows that subcellular localization of FOXO3a might be a potential biomarker for predicting response to the combination treatment with PI3K and autophagy inhibitors in PIK3CA-mutant cervical cancer patients.
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