tert-Butylhydroquinone mobilizes intracellular-bound zinc to stabilize Nrf2 through inhibiting phosphatase activity

High intracellular calcium amounts inhibit activation-induced proliferation of mouse T cells: Tert-butyl hydroquinone as an additive enhancer of intracellular calcium

Optimal T cell activation is critical to orchestrate adaptive immune responses. Calcium is critical for T cell activation and integrates signaling pathways necessary to activate key transcription factors. In fact, patients with calcium channelopathies are immunodeficient. Here, we investigated the effects of different concentrations of intracellular calcium on activation of mouse T cells. High intracellular calcium amounts inhibited in vitro T cell proliferation as evidenced by a decreased cell cycling-to-hypodiploidy ratio in two models of activation: the combination of phorbol 12-myristate 13-acetate (PMA) and Ionomycin (an ionophore)/Thapsigargin (a SERCA inhibitor) or plate bound anti-CD3 and anti-CD28. High intracellular calcium amounts increased the production of reactive oxygen species (ROS) in T cells activated with PMA and Ionomycin and scavenging excess ROS using N-acetyl cysteine (NAC) rescued the decrease in cycling-to-hypodiploidy ratio. To test the universality of our observations, we studied the effects of tert-Butylhydroquinone (tBHQ), a SERCA inhibitor and Nrf2 activator. tBHQ alone did not increase intracellular calcium amounts but the intracellular calcium amounts increased when tBHQ was used in combination with PMA. Also, tBHQ inhibited T cell activation in a dose-dependent manner in both in vitro models of T cell activation. Importantly, intraperitoneal injection of tBHQ ameliorated Dextran Sodium Sulfate (DSS)-induced colitis in mice as evidenced by rescue of colon length shortening and lower disease activity index. Overall, this study identifies high calcium amounts as a potential target to lower T cell activation. The implications of these observations are discussed in the context of calcium modulating drugs that are used to treat various diseases.

Keap1-Nrf2 Heterodimer: A Therapeutic Target to Ameliorate Sickle Cell Disease

Sickle cell disease (SCD) is a monogenic inheritable disease characterized by severe anemia, increased hemolysis, and recurrent, painful vaso-occlusive crises due to the polymerization of hemoglobin S (HbS)-generated oxidative stress. Up until now, only four drugs are approved for SCD in the US. However, each of these drugs affects only a limited array of SCD pathologies. Importantly, curative therapies, such as gene therapy, or hematopoietic stem cell transplantation are not available for every patient because of their high costs, availability of donor matching, and their serious adverse effects. Therefore, there is an unmet medical need for novel therapeutic strategies that target broader SCD sequelae. SCD phenotypic severity can be alleviated by increasing fetal hemoglobin (HbF) expression. This results in the inhibition of HbS polymerization and thus sickling, and a reduction in oxidative stress. The efficacy of HbF is due to its ability to dilute HbS levels below the threshold required for polymerization and to influence HbS polymer stability in RBCs. Nuclear factor-E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein-1 (Keap1)-complex signaling is one of the most important cytoprotective signaling controlling oxidative stress. Nrf2 is present in most organs and, after dissociation from Keap1, it accumulates in the cytoplasm, then translocates to the nucleus where it binds to the antioxidant response element (ARE) sequences and increases the expression of various cytoprotective antioxidant genes. Keeping this in mind, various researchers have proposed a role of multiple agents, more importantly tert-Butylhydroquinone (tBHQ), curcumin, etc., (having electrophilic properties) in inhibiting keap1 activity, so that Nrf2 can translocate to the nucleus to activate the gamma globin gene, thus maintaining alpha-hemoglobin-stabilizing protein (AHSP) and HbF levels. This leads to reduced oxidative stress, consequently minimizing SCD-associated complications. In this review, we will discuss the role of the Keap-1–Nrf2 complex in hemoglobinopathies, especially in SCD, and how this complex might represent a better target for more effective treatment options.

Induction of Cardiac Pathology: Endogenous versus Exogenous Nrf2 Upregulation

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of the endogenous antioxidant response to reactive oxygen species as well as a controller of Phase II detoxification in response to xenobiotics. This amenity to specific external manipulation exploits the binding affinity of Nrf2 for its constitutive repressor and degradation facilitator Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1). Derived from both natural and synthesized origins, these compounds have been extensively tested without definitive beneficial results. Unfortunately, multiple terminated trials have shown a negative side to Nrf2 with regard to cardiac pathologies while animal-based studies have demonstrated cardiomyocyte hypertrophy and heart failure after chronic Nrf2 upregulation. Putatively based on autophagic control of Nrf2 activity-modulating upstream factors, new evidence of miRNA involvement has added complexity to this mechanism. What follows is an extensive survey of Nrf2-regulating exogenous compounds that may promote cardiomyopathy, clinical trial evidence, and a comparison to exercise-induced factors that also upregulate Nrf2 while preventing cardiac pathologies.

NRF2: A crucial regulator for mitochondrial metabolic shift and prostate cancer progression

Metabolic alterations are a common survival mechanism for prostate cancer progression and therapy resistance. Oxidative stress in the cellular and tumor microenvironment dictates metabolic switching in the cancer cells to adopt, prosper and escape therapeutic stress. Therefore, regulation of oxidative stress in tumor cells and in the tumor-microenvironment may enhance the action of conventional anticancer therapies. NRF2 is the master regulator for oxidative stress management. However, the overall oxidative stress varies with PCa clinical stage, metabolic state and therapy used for the cancer. In agreement, the blanket use of NRF2 inducers or inhibitors along with anticancer therapies cause adverse effects in some preclinical cancer models. In this review, we have summarized the levels of oxidative stress, metabolic preferences and NRF2 activity in the different stages of prostate cancer. We also propose condition specific ways to use NRF2 inducers or inhibitors along with conventional prostate cancer therapies. The significance of this review is not only to provide a detailed understanding of the mechanism of action of NRF2 to regulate oxidative stress-mediated metabolic switching by prostate cancer cells to escape the radiation, chemo, or hormonal therapies, and to grow aggressively, but also to provide a potential therapeutic method to control aggressive prostate cancer growth by stage specific proper use of NRF2 regulators.

tert-Butylhydroquinone-induced formation of high-molecular-weight p62: A novel mechanism in the activation of Nrf2-Keap1

The respiratory system is always exposed to air and is most vulnerable to attack by environmental free radicals. The nuclear factor E2-related factor 2-Kelch-like ECH-associated protein 1-antioxidant response element (Nrf2-Keap1-ARE) pathway and p62 are both involved in the oxidative stress response. However, the interplay between these two systems remains largely unknown. This study shows that treatment of L2 cells with tert-Butylhydroquinone (tBHQ) generates a high-molecular-weight (HMW) form of p62, leading to activation of the Nrf2-Keap1-ARE pathway. The levels of HMW-p62 increased as the tBHQ concentration increased, with concomitant decreases seen in the classical form of p62. Moreover, small interfering RNA targeting p62 increases Keap1 protein levels and inactivates the Nrf2-Keap1-ARE pathway. These results demonstrate that the Nrf2-Keap1 pathway is partially regulated by p62. tBHQ-induced HMW-p62 production may be a novel mechanism in the activation of the Nrf2-Keap1-ARE pathway.

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.

Diverse cellular actions of tert-butylhydroquinone, a food additive, on rat thymocytes

Tertiary butylhydroquinone (TBHQ) is a food additive that possesses antioxidant activity. Its alternative applications have been explored in recent studies. However, there is controversy regarding safety. In this study using rat thymocytes, the cellular actions of TBHQ at sublethal concentrations were examined. TBHQ at concentrations of 3 μM or more elevated intracellular Zn²⁺ concentration ([Zn²⁺]_i) in a dose-dependent manner, by increasing membrane Zn²⁺ permeability and releasing Zn²⁺ from cellular stores. TBHQ at 30 μM significantly increased side scatter (cell density) and the exposure of phosphatidylserine (PS) on cell membrane surfaces. It also decreased cellular glutathione (GSH) content without affecting cell lethality. Forward scatter was attenuated by 100 μM TBHQ. Thus, it is considered that TBHQ at sublethal concentrations (30 μM or less) exerts some adverse actions on cells. TBHQ at 10-30 μM attenuated the increase in cell lethality induced by hydrogen peroxide (H₂O₂), while potentiation of H₂O₂ cytotoxicity by 100 μM TBHQ was observed. The range of concentrations of TBHQ from benefit to toxicity under in vitro conditions may be 10-30 μM. Although TBHQ exhibits antioxidative actions at concentrations that are lower than those which elicit adverse cellular effects, sublethal levels of TBHQ cause some adverse actions that may be clinically concerned.

HX-1171, a Novel Nrf2 Activator, Induces NQO1 and HMOX1 Expression

HX-1171 (1-O-hexyl-2,3,5-trimethylhydroquinone) is a novel synthesized vitamin E derivative, which reportedly has positive effects on various diseases and conditions, such as liver fibrosis, hepatic cirrhosis, and cancer. In this study, we analyzed the transcriptional activity induced by HX-1171. Results from reverse transcription polymerase chain reaction and promoter assays reveal that HX-1171 increased the expression of NQO1 and HMOX1, encoding antioxidant-related enzymes, in A549 human lung epithelial cells. The activity of nuclear factor-E2-related factor (Nrf2), a key transcriptional factor for antioxidative enzymes, was examined in HX-1171-treated cells. Confocal microscopy and Western blotting showed that HX-1171 effectively induced the nuclear translocation and transcriptional activity of Nrf2. We conclude that HX-1171, a novel Nrf2 activator, may be a promising therapeutic agent for oxidative stress-induced diseases. J. Cell. Biochem. 118: 3372-3380, 2017. © 2017 Wiley Periodicals, Inc.

Nuclear factor-like factor 2-antioxidant response element signaling activation by tert-butylhydroquinone attenuates acute heat stress in bovine mammary epithelial cells

Nuclear factor (erythroid-derived 2)-like factor 2 (Nrf2) is a transcription factor that binds to the antioxidant response element (ARE) in the upstream promoter region of many antioxidative genes. The Nrf2-ARE signaling plays a key role in the cellular antioxidant-defense system, but whether Nrf2 activation has protective effects against heat shock (HS) stress in mammary epithelial cells (MEC) remains unclear. The objective of this study was to determine whether tert-butylhydroquinone (tBHQ), a well-known Nrf2 activator, could attenuate heat stress-induced cell damage in MAC-T cells of the bovine MEC line. The MAC-T cells were exposed to HS (42.5°C for 1h) followed by recovery at 37°C to mimic HS. Compared with cells that were consistently cultured at normothermia (37°C), the cell viability levels significantly decreased after HS stress. In parallel, heat stress increased the reactive oxygen species levels and induced cellular apoptosis and endoplasmic reticulum stress. The MAC-T cells that were pretreated with tBHQ (10μM) for 2h followed by HS had a reduction in the loss of cell viability. The tBHQ pretreatment significantly decreased cellular reactive oxygen species levels and stress-related marker gene expression. The tBHQ-treated MAC-T cells showed strong Nrf2-ARE signaling activation and a nuclear accumulation of Nrf2 and upregulated expression of Nrf2-ARE downstream genes. Small interfering RNA silencing of Nrf2 in HS-treated MAC-T cells almost completely abolished the cytoprotective effects by tBHQ. Overall, our results demonstrated that HS could cause cell damage in cultured bovine MEC, and that activation of Nrf2 by tBHQ could attenuate HS-induced cell damage.

Tumor Suppressor Lzap Suppresses Wnt/β-Catenin Signaling to Promote Zebrafish Embryonic Ventral Cell Fates via the Suppression of Inhibitory Phosphorylation of Glycogen Synthase Kinase 3

Wnt/β-catenin signaling controls various cell fates in metazoan development, and its dysregulation is often associated with cancer formation. However, regulations of this signaling pathway are not completely understood. Here, we report that Lzap, a tumor suppressor, controls nuclear translocation of β-catenin. In zebrafish embryos disruption of lzap increases the expression of chordin (chd), which encodes a bone morphogenetic protein (BMP) antagonist that is localized in prospective dorsal cells and promotes dorsal fates. Consistently, lzap-deficient embryos with attenuated BMP signaling are dorsalized, which can be rescued by overexpression of zebrafish lzap or bmp2b or human LZAP. The expansion of chd expression in embryos lacking lzap is due to the accumulation of nuclear β-catenin in ventral cells, in which β-catenin is usually degraded. Furthermore, the activity of GSK3, a master regulator of β-catenin degradation, is suppressed in lzap-deficient embryos via inhibitory phosphorylation. Finally, we also report that a similar regulatory axis is also likely to be present in a human tongue carcinoma cell line, SAS. Our results reveal that Lzap is a novel regulator of GSK3 for the maintenance of ventral cell properties and may prevent carcinogenesis via the regulation of β-catenin degradation.