Hrk Mediates 2-Methoxyestradiol- Induced Mitochondrial Apoptotic Signaling in Prostate Cancer Cells
1Department of Urology, VA Medical Center and UCSF. Molecular Cancer Therapeutics
(Impact Factor: 5.68).
04/2013; 12(6). DOI: 10.1158/1535-7163.MCT-12-1187
Prostate cancer is one of the most prevalent cancers in males and ranks the second most common cause of cancer related deaths. 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, is a promising anticancer agent for various types of cancers. Although 2-ME has been shown to activate Jun N-terminal kinase (JNK) and mitochondrial dependent apoptotic signaling pathways, the underlying mechanisms including downstream effectors remain unclear. Here, we report that the human Bcl-2 homology 3 (BH3)-only protein harakiri (Hrk) is a critical effector of 2-ME-induced-JNK/mitochondria dependent apoptosis in prostate cancer cells. Hrk mRNA and protein are preferentially up-regulated by 2-ME, and Hrk induction is dependent on JNK activation of c-Jun. Hrk knockdown prevents 2-ME-mediated apoptosis by attenuating the decrease in mitochondrial membrane potential, subsequent cytochrome c (cyt c) release and caspase activation. Involvement of the pro-apoptotic protein Bak in this process suggested the possible interaction between Hrk and Bak. Thus, Hrk activation by 2-ME or its over-expression displaced Bak from the complex with anti-apoptotic protein Bcl-xL, while deletion of the Hrk BH3 domain abolished its interaction with Bcl-xL, reducing the pro-apoptotic function of Hrk. Finally, Hrk is also involved in the 2-ME-mediated reduction of X-linked inhibitor of apoptosis (XIAP) through Bak activation in prostate cancer cells. Together, our findings suggest that induction of the BH3-only protein Hrk is a critical step in 2-ME activation of the JNK-induced apoptotic pathway targeting mitochondria by liberating pro-apoptotic protein Bak.
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- "Control and HDAC1/2-Ablated Retinae After Injury JNK is a member of the mitogen-activated protein kinase family (also known as the stress-activated protein kinases or SAPKs) that is activated in response to a variety of cellular stresses. Sustained activation contributes to cell death through different targets including c-Jun (Whitfield et al., 2001; Ma et al., 2007, p. 53; Fuchs et al., 1998a, 1998b) and Hrk (Chang et al., 2013). Previous studies have demonstrated that JNK signaling and its target transcription factor c-Jun are activated in RGCs following optic nerve injury. "
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ABSTRACT: Histones deacetylases (HDACs), besides their function as epigenetic regulators, deacetylate and critically regulate the activity of nonhistone targets. In particular, HDACs control partially the proapoptotic activity of p53 by balancing its acetylation state. HDAC inhibitors have revealed neuroprotective properties in different models, but the exact mechanisms of action remain poorly understood. We have generated a conditional knockout mouse model targeting retinal ganglion cells (RGCs) to investigate specifically the functional role of HDAC1 and HDAC2 in an acute model of optic nerve injury. Our results demonstrate that combined HDAC1 and HDAC2 ablation promotes survival of axotomized RGCs. Based on global gene expression analyses, we identified the p53-PUMA apoptosis-inducing axis to be strongly activated in axotomized mouse RGCs. Specific HDAC1/2 ablation inhibited this apoptotic pathway by impairing the crucial acetylation status of p53 and reducing PUMA expression, thereby contributing to the ensuing enhanced neuroprotection due to HDAC1/2 depletion. HDAC1/2 inhibition and the affected downstream signaling components emerge as specific targets for developing therapeutic strategies in neuroprotection.
© The Author(s) 2015.
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ABSTRACT: Estradiol (E2) is a steroid hormone whose physiological actions are mainly mediated by its interaction with intracellular estrogen receptors (ER) leading to modification on the mRNA and protein synthesis in its target cells. However, estrogens can also activate several intracellular signal transduction cascades by non-genomic mechanisms. Estrogens must be inactivated and removedfromblood through its conversion to soluble compounds with an apparent low estrogenic activity and decreased affinity for ER. In this context, 2-methoxyestradiol (2ME2) is generated by a sequential hydroxylation of E2 via the enzyme cytochrome P450 isoform 1A1 to produce 2-hydroxyestradiol (2OHE2) followed by a conjugation reaction catalyzed by the enzyme Catechol-O-Methyltransferase generating 2ME2 from 2OHE2.Recent evidence indicates that physiological concentration of 2ME2 may regulate several biological processes while high concentrations of this metabolite may induce pathophysiological alterations in several tissues. In the last years, 2ME2 has also been described as a promising anticancer drug although its cellular and molecular mechanisms arestillbeingdisclosed. Herein, we will review the available literature concerning the role of 2ME2 in health and disease. We will focus on to describing the intracellular mechanisms by which 2ME2exerts its effects on reproductive and non-reproductive tissues. The promising anticancer effects of 2ME2 and its synthetic derivatives will also be discussed. Finally, a group of 2ME2-target genes thatcould be used as biomarkers of 2ME2 under physiological or pathophysiological conditions will be reviewed.
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ABSTRACT: 2-Methoxyestradiol (2ME2) is an endogenous metabolite of estrogen that is nonestrogenic and has been studied in cancer as an antimitotic agent that is beneficial by its selectivity for cancer cells without toxicity to nonmalignant cells. Because the effect of 2ME2 in a transplant rejection setting remains unknown, we hypothesized that 2ME2 can inhibit stimulated T-cell function.
Human peripheral blood mononuclear cells (PBMCs) were cultured and pretreated with 2ME2 before stimulation. The cultured medium was collected for enzyme-linked immunosorbent assays, and whole-cell lysates were collected for Western immunoblotting. Proliferation and apoptosis assays were performed and analyzed by means of flow cytometry.
Tumor necrosis factor -α and interferon-γ cytokine production in 2ME2-treated stimulated PBMCs were modestly reduced relative to control samples. T-cell proliferation was blunted by treatment with 2ME2, and a decrease in apoptosis correlated with a decrease in caspase-9 activity. Additionally, 2ME2 was able to block stress-induced senescence caused by stimulation of T-cells.
2ME2 is a hormone-based therapy that blunts stimulated T-cell proliferation and does not induce apoptosis or stress-induced senescence. Stimulated T-cells treated with 2ME2 are still able to produce normal levels of cytokines. Therefore, 2ME2 may lead to an oral immunomodulatory adjunct therapy with a low side effect profile for individuals undergoing transplantation.
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