Journal
FREE RADICAL BIOLOGY AND MEDICINE
Volume 53, Issue 10, Pages 1929-1941Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.freeradbiomed.2012.08.595
Keywords
Estrogen receptor; Superoxide anions; mTORC2; ROS; Redox signaling; Free radicals
Funding
- Central Drug Research Institute
- CSIR India [CSIR-NWP0034, CSIR-EMPOWER]
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The estrogen receptor (ER) plays a cardinal role in estrogen-responsive breast carcinogenesis. It is, however, unclear as to how estrogen-ER interaction potentiates breast cancer progression. Compelling evidence supports estrogen-induced redox alterations, such as augmented reactive oxygen species (ROS) levels, as having a crucial role in breast carcinogenesis. Despite ER being a biological mediator of the majority of estrogen-induced cellular responses; its role in estrogen-induced tissue-specific ROS generation remains largely debatable. We examined a panel of human breast cancer specimens and found that ER-positive breast cancer specimens exhibited a higher incidence of augmented O-2(center dot-) levels compared to matched normal tissue. ROS are known to function as signal transducers and ROS-mediated signaling remains a key complementary mechanism that drives carcinogenesis by activating redox-sensitive oncogenic pathways. Additional studies revealed that augmented O-2(center dot-) levels in breast cancer specimens coincided with mammalian target of rapamycin complex 2 (mTORC2) hyperactivation. Detailed investigations using in vitro experiments established that 17 beta-estradiol (E2)-stimulated breast cancer cells exhibited transiently upregulated O-2(center dot-) levels, with the presence of ER being a crucial determinant for the phenomenon to take place. Gene expression, ER transactivation, and confocal studies revealed that the E2-induced transient O-2(center dot-) upregulation was effected by ER through a nongenomic pathway possibly involving mitochondria. Furthermore, E2 treatment activated mTORC2 in breast cancer cells in a characteristically ER-dependent manner. Interestingly, altering O-2(center dot-) anion levels through chemical/genetic methods caused significant modulation of the mTORC2 signaling cascade. Taken together, our findings unravel a novel nongenomic pathway unique to estrogen-responsive breast cancer cells wherein, upon stimulation by E2. ER may regulate mTORC2 activity in a redoxdependent manner by transiently modulating O-2(center dot-) levels particularly within mitochondria. The findings suggest that therapies aimed at counteracting these redox alterations and/or resultant signaling cascades may complement conventional treatments for estrogen-responsive breast cancer. (C) 2012 Elsevier Inc. All rights reserved.
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