Abstract
There is a large body of scientific evidence suggesting that 3,3′-Diindolylmethane (DIM), a compound derived from the digestion of indole-3-carbinol, which is abundant in cruciferous vegetables, harbors anti-tumor activity in vitro and in vivo. Accumulating evidence suggests that AMP-activated protein kinase (AMPK) plays an essential role in cellular energy homeostasis and tumor development and that targeting AMPK may be a promising therapeutic option for cancer treatment in the clinic. We previously reported that a formulated DIM (BR-DIM; hereafter referred as B-DIM) with higher bioavailability was able to induce apoptosis and inhibit cell growth, angiogenesis, and invasion of prostate cancer cells. However, the precise molecular mechanism(s) for the anti-cancer effects of B-DIM have not been fully elucidated. In the present study, we investigated whether AMP-activated protein kinase (AMPK) is a molecular target of B-DIM in human prostate cancer cells. Our results showed, for the first time, that B-DIM could activate the AMPK signaling pathway, associated with suppression of the mammalian target of rapamycin (mTOR), down-regulation of androgen receptor (AR) expression, and induction of apoptosis in both androgen-sensitive LNCaP and androgen-insensitive C4-2B prostate cancer cells. B-DIM also activates AMPK and down-regulates AR in androgen-independent C4-2B prostate tumor xenografts in SCID mice. These results suggest that B-DIM could be used as a potential anti-cancer agent in the clinic for prevention and/or treatment of prostate cancer regardless of androgen responsiveness, although functional AR may be required.
Highlights
AMP-activated protein kinase (AMPK) is expressed in all eukaryotic cells and is a critical enzyme that plays an essential role in cellular energy homeostasis, as well as controlling processes related to tumor development including cell cycle progression, cell proliferation, protein synthesis, and survival
Both cell lines were treated with different concentrations of B-DIM for 3 hours, and cell lysates of the treated cells were analyzed by Western blot to measure the levels of phosphor-AMPKa (T172), an active form of AMPK protein, as well as some downstream target proteins
The results showed that the level phosphor-AMPKa in both prostate cancer cell lines treated with B-DIM increased in a dose-dependent manner (Fig. 1A, B)
Summary
AMP-activated protein kinase (AMPK) is expressed in all eukaryotic cells and is a critical enzyme that plays an essential role in cellular energy homeostasis, as well as controlling processes related to tumor development including cell cycle progression, cell proliferation, protein synthesis, and survival. In the regulation of metabolic process, AMPK phosphorylates serine moieties in many target proteins and results in switching on of catabolic pathways to activate ATP-generating processes including the uptake and oxidation of glucose and fatty acids, and switching off of anabolic pathways including protein, fatty acid and cholesterol syntheses, which consume ATP [6]. Regarding non-metabolic functions of AMPK, activation of AMPK can induce cell cycle arrest and inhibit cell proliferation and protein synthesis in malignant cells through multiple mechanisms such as the accumulation of tumor suppressor factor p53 and the cyclindependent kinase inhibitors p21 and p27 [7], as well as downregulation of the mTOR pathway [8,9]. Extensive research supports the role of AMPK in cancer prevention and therapeutics, suggesting that targeting AMPK may be a promising option for cancer treatment
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