tretinoin and 2-tert-butylhydroquinone

Alzheimer's disease (AD) a progressive neurodegenerative disorder of later life, is characterized by brain deposition of amyloid beta-protein (Abeta) plaques, accumulation of intracellular neurofibrillatory tangles, synaptic loss and neuronal cell death. There is significant evidence that oxidative stress is a critical event in the pathogenesis of AD. In the present study Abeta formation was induced in NT2N neurons, one of the most appropriate cell line models in AD. Our results indicate that oxidative stress resulting from the treatment of H(2)O(2)/FeSO(4) and/or 4-hydroxy-2-noenal (HNE) can be inhibited in the presence of tBHQ, a known inducer of nuclear factor-erythroid 2 related factor 2 (Nrf2) in NT2N neurons and can therefore be used to elucidate the relationship between oxidative stress, Abeta formation and Nrf2. The role of Nrf2 was confirmed using retinoic acid as an inhibitor of Nrf2. It provides the first documentation that tBHQ not only protects the neurons against cell death but also decreases amyloid beta formation. Moreover, the results indicate that oxidative stress fosters Abeta formation in NT2N neurons, creating a vicious neurodegenerative loop.

Topics: Aldehydes; Alzheimer Disease; Amyloid beta-Peptides; Animals; Antineoplastic Agents; Antioxidants; Astrocytes; Caspase 3; Cell Line; Cysteine Proteinase Inhibitors; Enzyme Activation; Ferrous Compounds; Glutathione; Humans; Hydrogen Peroxide; Hydroquinones; Neurons; NF-E2-Related Factor 2; Oxidants; Oxidative Stress; Tretinoin

Isothiocyanates and phenolic antioxidants can prevent cancer through activation of Nrf2 (NF-E2 p45-related factor 2), a transcription factor that controls expression of cytoprotective genes through the antioxidant response element (ARE) enhancer. Using a human mammary MCF7-derived AREc32 reporter cell line, we now report that all-trans retinoic acid (ATRA), and other retinoic acid receptor alpha (RARalpha) agonists, markedly reduces the ability of Nrf2 to mediate induction of ARE-driven genes by cancer chemopreventive agents including the metabolite of butylated hydroxyanisole, tert-butylhydroquinone (tBHQ). The basal and tBHQ-inducible expression of aldo-keto reductase (AKR) AKR1C1 and AKR1C2 genes, which are regulated by Nrf2, was also repressed by ATRA in AREc32 cells. Antagonists of RARalpha augmented induction of ARE-driven gene expression by tBHQ, as did knockdown of RARalpha by using RNAi. The expression of the ARE-gene battery was increased in the small intestine of mice fed on a vitamin A-deficient diet, and this increase was repressed by administration of ATRA. By contrast, in the small intestine of Nrf2 null mice, the expression of ARE-driven genes was not affected by vitamin A status. In MCF7 cells, ATRA did not block the nuclear accumulation of Nrf2 but reduced the binding of Nrf2 to the ARE enhancer as a consequence of forming a complex with RARalpha. These data suggest that cross-talk between Nrf2 and RARalpha could markedly influence the sensitivity of cells to electrophiles and oxidative stressors and, as a consequence, to carcinogenesis.

Topics: 20-Hydroxysteroid Dehydrogenases; Animals; Antineoplastic Agents; Antioxidants; Cell Line, Tumor; Cell Nucleus; Chemoprevention; Enhancer Elements, Genetic; Gene Expression; Humans; Hydroquinones; Hydroxysteroid Dehydrogenases; Luciferases; Mice; Mice, Mutant Strains; Neoplasms; NF-E2 Transcription Factor, p45 Subunit; Receptors, Retinoic Acid; Response Elements; Retinoic Acid Receptor alpha; Tretinoin

Sarco-endoplasmic reticulum calcium ATPase (SERCA) enzymes control calcium-induced cellular activation by accumulating calcium from the cytosol into the endoplasmic reticulum (ER). To better understand the role of SERCA proteins and cellular calcium homeostasis in all-trans retinoic acid (ATRA)-induced differentiation, we investigated the effect of pharmacologic inhibition of SERCA-dependent calcium uptake into the ER on ATRA-induced differentiation of the HL-60 myelogenous and the NB4 promyelocytic cell lines. SERCA inhibitors di-tert-butyl-benzohydroquinone (tBHQ), thapsigargin, and cyclopiazonic acid significantly enhanced the induction of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and CD11b marker expression induced by suboptimal concentrations of ATRA (50 nM) in both cell lines. Analysis of cellular calcium homeostasis revealed that a 60% mobilization of the total SERCA-dependent intracellular calcium pool was necessary to obtain enhancement of ATRA-dependent differentiation by tBHQ. Moreover, after 3 days of ATRA treatment in combination with tBHQ, NB4 cells showed a significantly decreased calcium mobilization compared with treatments with tBHQ or ATRA alone, suggesting that enhanced differentiation and calcium mobilization are causally related. Interestingly, several ATRA-resistant NB4-derived cell lines were partially responsive to the differentiation-inducing effect of the combination of the 2 drugs. In addition, we found that retinoic acid receptor alpha (RAR alpha) and PML-RAR alpha proteins are protected from ATRA-induced proteolytic degradation by SERCA inhibition, indicating that cellular calcium homeostasis may interact with signaling systems involved in the control of ATRA-dependent transcriptional activity. By linking calcium to ATRA-dependent signaling, our data open new avenues in the understanding of the mechanisms of differentiation-induction therapy of leukemia.

Topics: Calcium; Calcium Signaling; CD11b Antigen; Cell Differentiation; Drug Synergism; Endoplasmic Reticulum; Gene Expression Regulation, Leukemic; HL-60 Cells; Homeostasis; Humans; Hydroquinones; Indoles; Leukemia, Promyelocytic, Acute; NADPH Oxidases; Neoplasm Proteins; Oncogene Proteins, Fusion; Receptors, Retinoic Acid; Retinoic Acid Receptor alpha; Thapsigargin; Transcription, Genetic; Tretinoin; Tumor Cells, Cultured