Expression of the p53 tumor suppressor gene is up-regulated by depletion of intracellular zinc in HepG2 cells

Nutrition and melanoma: the contribution of trace elements in onset, progression, and treatment of melanoma

Melanoma is a highly malignant and drug-resistant disease that imposes a substantial economic burden on the world. There are many studies linking trace elements to diverse types of cancers, including melanoma. This review elucidates the relationship between trace elements exposure and melanoma. It was identified that copper, manganese, selenium, zinc, iron, and many other trace elements were associated with melanoma in humans. In terms of epidemiology, different elements have different correlations with melanoma. These trace elements affect the occurrence and development of melanoma through various mechanisms, such as oxidative stress and the MAPK pathway. The literature on the role of trace elements in the pathogenesis and treatment of melanoma depicts promising prospects for this field.

The Zinc Transporter SLC39A10 Plays an Essential Role in Embryonic Hematopoiesis

The role of zinc in hematopoiesis is currently unclear. Here, SLC39A10 (ZIP10) is identified as a key zinc transporter in hematopoiesis. The results show that in zebrafish, Slc39a10 is a key regulator of the response to zinc deficiency. Surprisingly, both slc39a10 mutant zebrafish and hematopoietic Slc39a10-deficient mice develop a more severe form of impaired hematopoiesis than animals lacking transferrin receptor 1, a well-characterized iron gatekeeper, indicating that zinc plays a larger role than iron in hematopoiesis, at least in early hematopoietic stem cells (HSCs). Furthermore, it is shown that loss of Slc39a10 causes zinc deficiency in fetal HSCs, which in turn leads to DNA damage, apoptosis, and G₁ cell cycle arrest. Notably, zinc supplementation largely restores colony formation in HSCs derived from hematopoietic Slc39a10-deficient mice. In addition, inhibiting necroptosis partially restores hematopoiesis in mouse HSCs, providing mechanistic insights into the requirement for zinc in mediating hematopoiesis. Together, these findings indicate that SLC39A10 safeguards hematopoiesis by protecting against zinc deficiency-induced necroptosis, thus providing compelling evidence that SLC39A10 and zinc homeostasis promote the development of fetal HSCs. Moreover, these results suggest that SLC39A10 may serve as a novel therapeutic target for treating anemia and zinc deficiency-related disorders.

Zinc supplementation and its benefits in the management of chronic liver disease: An in-depth literature review

Malnutrition among patients with chronic liver disease (CLD) is a common complication with significant prognostic implications for patients with liver cirrhosis. Micronutrient deficiency has been associated with an increased risk of hepatic decompensation and is an independent risk factor for mortality among cirrhotic patients. Micronutrient deficiencies in patients with CLD include zinc, vitamin A, vitamin D and selenium. This review article aims to evaluate the literature to date on the complications of zinc deficiency in patients with CLD. A management algorithm for zinc replacement has also been proposed.

Zinc Prevents DNA Damage in Normal Cells but Shows Genotoxic and Cytotoxic Effects in Acute Myeloid Leukemia Cells

Genomic instability is prevented by the DNA damage response (DDR). Micronutrients, like zinc (Zn), are cofactors of DDR proteins, and micronutrient deficiencies have been related to increased cancer risk. Acute myeloid leukemia (AML) patients commonly present Zn deficiency. Moreover, reports point to DDR defects in AML. We studied the effects of Zn in DDR modulation in AML. Cell lines of AML (HEL) and normal human lymphocytes (IMC) were cultured in standard culture, Zn depletion, and supplementation (40 μM ZnSO₄) conditions and exposed to hydrogen peroxide (H₂O₂) or ultraviolet (UV) radiation. Chromosomal damage, cell death, and nuclear division indexes (NDI) were assessed through cytokinesis-block micronucleus assay. The phosphorylated histone H2AX (yH2AX) expression was monitored at 0 h, 1 h, and 24 h after exposure. Expression of DDR genes was evaluated by quantitative real time polymerase chain reaction (qPCR). Zn supplementation increased the genotoxicity of H₂O₂ and UV radiation in AML cells, induced cytotoxic and antiproliferative effects, and led to persistent yH2AX activation. In contrast, in normal lymphocytes, supplementation decreased damage rates, while Zn depletion favored damage accumulation and impaired repair kinetics. Gene expression was not affected by Zn depletion or supplementation. Zn presented a dual role in the modulation of genome damage, preventing damage accumulation in normal cells and increasing genotoxicity and cytotoxicity in AML cells.

Isoforms of the p53 Family and Gastric Cancer: A Ménage à Trois for an Unfinished Affair

Simple Summary

The p53 family is a complex family of transcription factors with different cellular functions that are involved in several physiological processes. A massive amount of data has been accumulated on their critical role in the tumorigenesis and the aggressiveness of cancers of different origins. If common features are observed, there are numerous specificities that may reflect particularities of the tissues from which the cancers originated. In this regard, gastric cancer tumorigenesis is rather remarkable, as it is induced by bacterial and viral infections, various chemical carcinogens, and familial genetic alterations, which provide an example of the variety of molecular mechanisms responsible for cell transformation and how they impact the p53 family. This review summarizes the knowledge gathered from over 40 years of research on the role of the p53 family in gastric cancer, which still displays one of the most elevated mortality rates amongst all types of cancers.

Abstract

Gastric cancer is one of the most aggressive cancers, with a median survival of 12 months. This illustrates its complexity and the lack of therapeutic options, such as personalized therapy, because predictive markers do not exist. Thus, gastric cancer remains mostly treated with cytotoxic chemotherapies. In addition, less than 20% of patients respond to immunotherapy. TP53 mutations are particularly frequent in gastric cancer (±50% and up to 70% in metastatic) and are considered an early event in the tumorigenic process. Alterations in the expression of other members of the p53 family, i.e., p63 and p73, have also been described. In this context, the role of the members of the p53 family and their isoforms have been investigated over the years, resulting in conflicting data. For instance, whether mutations of TP53 or the dysregulation of its homologs may represent biomarkers for aggressivity or response to therapy still remains a matter of debate. This uncertainty illustrates the lack of information on the molecular pathways involving the p53 family in gastric cancer. In this review, we summarize and discuss the most relevant molecular and clinical data on the role of the p53 family in gastric cancer and enumerate potential therapeutic innovative strategies.

Depletion of Endogenous Zinc Stores Induces Oxidative Stress and Cell Death in Human Melanoma Cells

The role of intracellular free zinc and its chelation by TPEN (N,N,N’,N’-tetrakis(2–pyridylmethyl)ethylenediamine) was studied in Bowes human melanoma cells. The content of free Zn pools was determined by fluorescent probe Zinquin. Depletion of zinc triggered apoptosis confirmed by cell blebbing, changes in mitochondrial transmembrane potential and GSH levels, caspase-3 activation and nuclear fragmentation. Apoptosis was only partially prevented by cyclosporin A or N-acetylcystein, suggesting various independent but likely interrelated mechanisms participating in this process.

Metal transporter Slc39a10 regulates susceptibility to inflammatory stimuli by controlling macrophage survival

Zn is essential for maintaining the integrity of the immune system, and Zn homeostasis is tightly regulated by two families of ion transporters, SLC39A and SLC30A. Worldwide, an estimated two billion people have Zn deficiency, a condition that can impair immune function and increase susceptibility to a variety of infections. Despite their important roles in health and disease, the molecular mechanisms that underlie Zn transport and Zn homeostasis in macrophages are poorly understood. Here, we report that SLC39A10 plays an essential role in Zn homeostasis in macrophages, regulating the immune response following inflammatory stimuli. Specifically, we identified a role for SLC39A10 in regulating the survival of macrophages via a Zn/p53-dependent axis during the inflammatory response.

Zn plays a key role in controlling macrophage function during an inflammatory event. Cellular Zn homeostasis is regulated by two families of metal transporters, the SLC39A family of importers and the SLC30A family of exporters; however, the precise role of these transporters in maintaining macrophage function is poorly understood. Using macrophage-specific Slc39a10-knockout (Slc39a10^fl/fl;LysM-Cre⁺) mice, we found that Slc39a10 plays an essential role in macrophage survival by mediating Zn homeostasis in response to LPS stimulation. Compared with Slc39a10^fl/fl mice, Slc39a10^fl/fl;LysM-Cre⁺ mice had significantly lower mortality following LPS stimulation as well as reduced liver damage and lower levels of circulating inflammatory cytokines. Moreover, reduced intracellular Zn concentration in Slc39a10^fl/fl;LysM-Cre⁺ macrophages led to the stabilization of p53, which increased apoptosis upon LPS stimulation. Concomitant knockout of p53 largely rescued the phenotype of Slc39a10^fl/fl;LysM-Cre⁺ mice. Finally, the phenotype in Slc39a10^fl/fl;LysM-Cre⁺ mice was mimicked in wild-type mice using the Zn chelator TPEN and was reversed with Zn supplementation. Taken together, these results suggest that Slc39a10 plays a role in promoting the survival of macrophages through a Zn/p53-dependent axis in response to inflammatory stimuli.

Zinc deficiency and neurodevelopment: the case of neurons

Zinc is essential for normal brain development. Gestational severe zinc deficiency can lead to overt fetal brain malformations. Although not teratogenic, suboptimal zinc nutrition during gestation can have long-term effects on the offspring's nervous system. This article will review current knowledge on the role of zinc in modulating neurogenesis and neuronal apoptosis as well as the proposed underlying mechanisms. A decrease in neuronal zinc causes cell cycle arrest, which in part involves a deregulation of select signals (ERK1/2, p53, and NF-kappaB). Zinc deficiency also induces apoptotic neuronal death through the intrinsic (mitochondrial) pathway, which can be triggered by the activation of the zinc-regulated enzyme caspase-3, and as a consequence of abnormal regulation of prosurvival signals (ERK1/2 and NF-kappaB). Alterations in the finely tuned processes of neurogenesis, neuronal migration, differentiation, and apoptosis, which involve the developmental shaping of the nervous system, could have a long-term impact on brain health. Zinc deficiency during gestation, even at the marginal levels observed in human populations, could increase the risk for behavioral/neurological disorders in infancy, adolescence, and adulthood.

Influence of zinc deficiency on Akt-Mdm2-p53 and Akt-p21 signaling axes in normal and malignant human prostate cells

Phosphorylated Akt (p-Akt), a phosphoinositide-3-OH-kinase-activated protein kinase, is highly expressed in prostate tumors. p-Akt can indirectly hinder p53-dependent growth suppression and apoptosis by phosphorylating Mdm2. Alternatively, p-Akt can directly phosphorylate p21 and restrict it to the cytoplasm for degradation. Because the prostate is the highest zinc-accumulating tissue before the onset of cancer, the effects of physiological levels of zinc on Akt-Mdm2-p53 and Akt-p21 signaling axes in human normal prostate epithelial cells (PrEC) and malignant prostate LNCaP cells were examined in the present study. Cells were cultured for 6 days in low-zinc growth medium supplemented with 0 [zinc-deficient (ZD)], 4 [zinc-normal (ZN)], 16 [zinc-adequate (ZA)], or 32 [zinc-supplemented (ZS)] microM zinc. Zinc status of both cell types was altered in a dose-dependent manner, with LNCaP cells reaching a plateau at >16 microM zinc. For both cell types, p-Akt was higher in the ZD than in the ZN cells and was normalized to that of the ZN cells by treatment with a PI3K inhibitor, LY-294002. PTEN, an endogenous phosphatase targeting Akt dephosphorylation, was hyperphosphorylated (p-PTEN, inactive form) in ZD PrEC. Nuclear p-Mdm2 was raised, whereas nuclear p53 was depressed, by zinc deficiency in PrEC. Nuclear p21 and p53 were lowered by zinc deficiency in LNCaP cells. Higher percentages of ZD, ZA, and ZS than ZN LNCaP cells were found at the G(0)/G(1) phase of the cell cycle, with proportionally lower precentages at the S and G(2)/M phases. Hence, the increased p-PTEN in ZD PrEC would result in hyperphosphorylation of p-Akt and p-Mdm2, as well as reduction of nuclear p53 accumulation. For ZD LNCaP cells, Akt hyperphosphorylation was probably mediated through p21 phosphorylation and degradation, thus restricting p21 nuclear entry to induce cell cycle arrest. Thus zinc deficiency differentially modulated the Akt-Mdm2-p53 signaling axis in normal prostate cells vs. the Akt-p21 signaling axis in malignant prostate cells.

The important role of the apoptotic effects of zinc in the development of cancers

Zinc is a trace element that is essential for the normal function of cells. It is a cofactor for the structure and function of a wide range of cellular proteins including enzymes, transcription factors, and structural proteins. Recent studies have shown that zinc plays a role in the development of various cancers. Unfortunately no established common relationships of zinc with cancer development and progression have been identified. Zinc is known to have systemic effects such as regulation of the immune system as well as direct cellular effects resulting in regulation of gene expression, bioenergetics, metabolic pathways, signal transduction and cell invasion. Zinc is also reported to regulate cell proliferation and growth. In this review presentation we focus on the effects of zinc that are involved in the regulation of apoptosis in malignant cells. We selected the apoptotic effects of zinc because zinc is reported to both induce apoptosis in some cancers and to protect other cancer cells against apoptosis induced by other factors. The effects of zinc in the regulation of apoptosis appear to be cell type specific. More importantly the reported effects of zinc on cancer cells must be viewed from the perspective of the physiological regulation of zinc homeostasis. Thus one must be mindful of the experimental conditions under which zinc effects are investigated relative to the physiological and pathological conditions of cellular zinc distribution and concentrations that can exist in situ.

Effect of resveratrol and zinc on intracellular zinc status in normal human prostate epithelial cells

To evaluate the influence of resveratrol on cellular zinc status, normal human prostate epithelial (NHPrE) cells were treated with resveratrol (0, 0.5, 1, 2.5, 5, and 10 microM) and zinc [0, 4, 16, and 32 microM, representing zinc-deficient (ZD), zinc-normal (ZN), zinc-adequate (ZA), and zinc-supplemented (ZS) conditions, respectively]. A progressive reduction in cell growth was observed in cells treated with increasing amounts of resveratrol (2.5-10 microM). Resveratrol at 5 and 10 microM resulted in a dramatic increase in cellular total zinc concentration, especially in ZS cells. Flow cytometry indicated that 10 microM resveratrol induced arrest of the cell cycle at the G(2)/M phase in association with the observed cell growth inhibition. Data from an in vitro experiment using zinquin as an indicator of intracellular free Zn(II) status demonstrated complex interactions between resveratrol and Zn(II). Fluorescence spectrofluorometry and fluorescence microscopic analyses revealed that intracellular free labile zinc was progressively elevated from nearly twofold in ZS cells with no resveratrol to multifold in ZA and ZS cells with 10 microM resveratrol compared with the corresponding ZN cells. Furthermore, increases in cellular zinc status were associated with elevated levels of reactive oxygen species and senescence, as evidenced by morphological and histochemical changes in cells treated with 2.5 or 10 microM resveratrol, especially in ZA and ZS cells. Taken together, the interaction between resveratrol and zinc in NHPrE cells increases total cellular zinc and intracellular free labile zinc status and, subsequently, reactive oxygen species production and senescence.

Nitric oxide-mediated protection of endothelial cells from hydrogen peroxide is mediated by intracellular zinc and glutathione

Oxidative stress may cause endothelial dysfunction and vascular disease. It has been shown that NO protects endothelial cells (EC) against H(2)O(2)-induced toxicity. In addition, it is known that NO within cells induces a zinc release from proteins containing zinc-sulfur complexes. The aim of this study was to investigate whether zinc released intracellularly by NO plays a signaling role in the NO-mediated protection against H(2)O(2) in rat aortic EC. Our results show that the NO-mediated protection toward H(2)O(2) depends on the activities of glutathione peroxidase and glutamate cysteine ligase (GCL), the rate-limiting enzyme of glutathione (GSH) de novo biosynthesis. Moreover, NO increases the synthesis of the antioxidant GSH by inducing the expression of the catalytic subunit of GCL (GCLC). Chelating intracellular "free" zinc abrogates the NO-mediated increase of GCLC and of cellular GSH levels. As a consequence, the NO-mediated protection against H(2)O(2)-induced toxicity is impaired. We also show that under proinflammatory conditions, both cellular NO synthesis and intracellular "free" zinc are required to maintain the cellular GSH levels. Using RNA interference and laser scanning microscopy, we found that the NO-induced expression of GCLC depends on the activation of the transcription factor Nrf2 but not on the activity of the "zinc-sensing" transcription factor MTF-1. These findings show that intracellular "free" zinc plays a signaling role in the protective activity of NO and could explain why maintenance of an adequate zinc status in the endothelium is important to protect from oxidative stress and the development of vascular disease.

Zinc protects endothelial cells from hydrogen peroxide via Nrf2-dependent stimulation of glutathione biosynthesis

Oxidative stress is one of the main causes of vascular disease. This study aims to investigate the antioxidant activity exerted by zinc in primary rat endothelial cells (EC). Using a 24-h treatment with hydrogen peroxide as a model for oxidative stress, we found that zinc supplementation protects from peroxide-induced cell death via increasing the transcription of the catalytic subunit (heavy chain) of glutamate-cysteine ligase (GCLC) and the concentrations of glutathione (GSH). Conversely, zinc depletion significantly decreased the expression of GCLC and the cellular GSH levels, resulting in an increased susceptibility of EC to oxidative stress. Using confocal microscopy and the RNA silencing technique, we found that zinc upregulates the expression of GCLC by activating the transcription factor Nrf2. Surprisingly, the intracellular zinc sensor, metal-responsive transcription factor-1, is not involved in the zinc-induced expression of GCLC. The present study shows that zinc controls the redox state of EC by regulating the de novo synthesis of GSH. This molecular mechanism may contribute to the elaboration of new nutritional and/or pharmaceutical approaches for protecting the endothelium against oxidative stress.

Zinc deficiency alters DNA damage response genes in normal human prostate epithelial cells

Zinc is an essential trace element for human health and is a critical component of many proteins and transcription factors involved in DNA damage response and repair. The prostate is known to accumulate high levels of zinc, but levels are markedly decreased with cancer development. We hypothesized that zinc plays a critical role in maintaining DNA integrity in the prostate and zinc deficiency would lead to increased DNA damage and altered DNA damage response mechanisms. To test this hypothesis, the goal of this study was to determine the effects of zinc deficiency on DNA damage and DNA repair mechanisms by examining changes in global gene expression and transcription factor binding abilities in normal prostate epithelial cells (PrEC). Increased single-strand DNA breaks (Comet assay) were observed in PrEC grown in zinc-deficient media compared with cells grown in zinc-adequate media for 7 d. Using Affymetrix HG-U133A gene chips, differential expression of genes involved in cell cycle, apoptosis, transcription, and DNA damage response and repair were identified with low cellular zinc. Among genes involved in DNA damage response and repair, tumor protein p73, MRE11 meiotic recombination 11 homolog A, X-ray repair complementing defective repair in Chinese hamster cells 4, and breast cancer 2, early onset were down-regulated and TP53 was up-regulated. Additionally, western blotting showed increased nuclear p53 protein expression with zinc deficiency. Despite increased p53 gene and nuclear protein expression, there was no significant change in p53 binding activity. Zinc deficiency also induced an increase in binding activity of transcription factors involved in regulating cell proliferation and apoptosis. Thus, zinc deficiency may compromise DNA integrity in the prostate by impairing the function of zinc-containing proteins.

Zinc deficiency depresses p21 gene expression: inhibition of cell cycle progression is independent of the decrease in p21 protein level in HepG2 cells

The influence of zinc status on p21 gene expression was examined in human hepatoblastoma (HepG2) cells. Cells were cultured for one passage in a basal medium depleted of zinc to induce severely zinc-deficient (ZD) cells or in basal medium supplemented with 0.4, 4.0, 16, or 32 μM zinc to represent mild zinc deficiency (ZD0.4), the amount of zinc in most normal media (ZN), the normal human plasma zinc level (zinc-adequate; ZA), or the high end of plasma zinc attainable by oral supplementation (ZS), respectively. In ZD and ZD0.4 cells, the nuclear p21 protein level, mRNA abundance, and promoter activity were reduced to 40, 70, and 65%, respectively, of ZN cells. However, p21 protein and mRNA levels, as well as p21 promoter activity, were not altered in ZA and ZS cells compared with ZN cells. Moreover, the amounts of acetylated histone-4 associated with the proximal and distal p21 promoter regions, as a measure of p21 promoter accessibility, were decreased in ZD (73 and 64%, respectively) and ZD0.4 (82 and 77%, respectively) cells compared with ZN cells (100 and 100%, respectively). Thus multiple lines of evidence indicate that the transcriptional process of p21 is downregulated by depressed zinc status in HepG2 cells. Furthermore, the transfection of 5 μg of plasmid cytomegalovirus-p21 plasmid, which constitutively expressed p21, was able to normalize the reduction in p21 protein level and cyclin D1-cdk4 complex activity but not the inhibition of cell growth and G1/S cell cycle progression in ZD cells.

Nuclear accumulations of p53 and Mdm2 are accompanied by reductions in c-Abl and p300 in zinc-depleted human hepatoblastoma cells

The influence of zinc status on the expression of proteins known to be involved in the stability of p53, the human tumor suppressor gene product, was examined in hepatoblastoma (HepG2) cells. Cells were cultured in zinc-deficient (ZD0.2, ZD0.4), zinc normal (ZN), zinc adequate (ZA), or zinc-supplemented (ZS) medium, which contained 0.2, 0.4, 4, 16, or 32 microM zinc, respectively. Nuclear p53 levels were almost 100% and 40% higher in ZD0.2 and ZD0.4 cells, respectively, than in ZN cells. Mdm2 protein, which mediates p53 degradation, was 174% and 148% higher in the nucleus of ZD0.2 and ZD0.4 cells, respectively, than in ZN cells. In addition, the observed reductions of nuclear c-Abl in ZD0.2 and ZD0.4 cells to 50% and 60% of ZN cells, respectively, may be a cellular response attempting to normalize nuclear p53 accumulation because nuclear c-Abl is known to down-regulate ubiquitination and nuclear export of p53. Moreover, no changes in total cellular p53, Mdm2, and c-Abl or nuclear Mdmx were observed among the treatment groups. Furthermore, in ZD0.2 and ZD0.4 cells, the reduction in total and nuclear p300, which is known to complex with CREB-binding protein and Mdm2 in the nucleus for the generation of degradable polyubiquitinated form of p53, may have depressed the degradation pathway for p53 and Mdm2, and contributed to the nuclear accumulation of these proteins in ZD cells.

Zinc deficiency-induced cell death

Zinc deficiency is characterized by an attenuation of growth factor signaling pathways and an amplification of p53 pathways. This outcome is facilitated by hypo-phosphorylation of AKT and ERK secondary to zinc deficiency, which are permissive events to the activation of the intrinsic cell death pathway. Low zinc concentrations provide an environment that is also conducive to the production of reactive oxygen/reactive nitrogen species (ROS/RNS) and caspase activation. Additionally, during zinc deficiency endogenous survival pathways such as NF-kappaB are inhibited in their transactivation potential. The above factors contribute to the irreversible commitment of the zinc deficient cell to death.

Metallothionein isoform 3 gene is differentially expressed in corticotropin-producing pituitary adenomas

In order to search for candidate genes related to pituitary adenoma aggressiveness, the present investigation was intended to compare the mRNA expression profile from a pool of four nonfunctional pituitary adenomas (NFPA) with a spinal cord metastasis of a nonfunctional pituitary carcinoma (MNFPC). The metallothionein isoform 3 (MT3) gene was differentially expressed in nonfunctional adenomas in comparison to the metastasis of nonfunctional carcinoma. A microarray dataset comprising 19,881 probes was employed for comparing expression profiles of a spinal cord metastasis of a nonfunctional pituitary carcinoma with a pool of four nonfunctional pituitary adenomas. RT-qPCR confirmed the microarray findings and was used to investigate MT3 mRNA gene expression in tumor samples of a series of 52 different pituitary adenoma subtypes comprising 10 corticotropin (ACTH)-producing, 18 growth hormone (GH)-producing, 8 prolactin (PRL)-producing, and 16 nonfunctional adenomas. Microarray data analysis by GeneSifter program unveiled Gene Ontology terms related to zinc ion-binding activity closely related to MT3 function. MT3 mRNA expression was statistically significantly higher in ACTH-producing pituitary adenomas and in nonfunctional pituitary adenomas in comparison to the other pituitary adenoma subtypes. The more abundant expression of this gene in ACTH-producing pituitary adenomas suggests that MT3 could be related to distinct pituitary cell lineage regulating the activity of some transcription factor of importance in hormone production and/or secretion.

Zinc inhibits the nuclear translocation of the tumor suppressor protein p53 and protects cultured human neurons from copper-induced neurotoxicity

High concentrations of the trace metal zinc (Zn) have previously been shown to provide transient protection of cells from apoptotic death. The molecular mechanisms responsible for this protection are not known. Thus, this work explored the ability of Zn to protect human neurons in culture (NT2-N) from Cu-mediated death and tested the hypotheses that the tumor-suppressor protein p53 plays a role in Cu-induced neuronal death and is part of the mechanism of Zn protection. Copper toxicity (100 microM) resulted in significant apoptotic neuronal death by 12 h. Addition of 100 microM Zn to Cu-treated cells increased neuronal death. However, the addition of 700 microM Zn to Cu-treated cells resulted in neuronal viability that was not different from untreated controls through 24 h. p53 mRNA abundance, while increased by the addition of Cu and 100 microM Zn, was decreased to 50% of control with the addition of 500 microM Zn in Cu-treated cells, and to 10% of control with 700 microM Zn. Consistent with its role as a transcription factor, both Western analysis and immunocytochemistry showed significant increases in nuclear p53 protein levels in Cu toxicity. The role of p53 in Cu-mediated apoptosis was further confirmed by elimination of apoptosis in Cu-treated cells that had been transfected with a dominant-negative p53 construct to prevent p53 expression. Furthermore, the addition of 500-700 microM Zn prevented the movement of p53 into the nucleus suggesting that Zn not only protects neurons from Cu toxicity by regulating p53 mRNA abundance but also by preventing the translocation of p53 to the nucleus.

Zinc depletion reduced Egr-1 and HNF-3beta expression and apolipoprotein A-I promoter activity in Hep G2 cells

We examined the influence of zinc status on expression of certain transcription factors involved in regulation of apolipoprotein A-I (apoAI) expression in human hepatoblastoma Hep G2 cells. A low zinc basal medium (zinc deficient, ZD) consisting of DMEM and 10% Chelex100-treated fetal bovine serum was used to deplete cellular zinc over one passage. Cells were also cultured for one passage in medium supplemented with 0.4 (ZD0.4), 4.0 (zinc normal, ZN), 16.0 (zinc adequate, ZA), or 32.0 microM zinc (zinc supplemented, ZS). Compared with ZN cells, cellular zinc levels were 43 and 31% lower in ZD and ZD0.4 cells but 70 and 146% higher in ZA and ZS cells, respectively. Supplementation of 0.4 microM zinc significantly increased DNA contents per plate, from 65% in ZD cells to 83% in ZD0.4 cells compared with ZN cells. Addition of >4 microM zinc in medium did not further increase DNA contents. The proportion of cells in G(1)/S and S phase was about fourfold higher and threefold lower, respectively, in ZD cells compared with ZN and other groups. Nuclear Egr-1 protein was markedly decreased in ZD and ZD0.4 cells. Moreover, hepatocyte nuclear factor (HNF)-3beta was severely degraded in ZD and ZD0.4 cells. In contrast, HNF-4alpha remained stable in all groups and was not significantly lower in ZD and ZD0.4 cells. Furthermore, downregulation of trans-acting factor Egr-1 and cleavage of HNF-3beta were associated with reduction of apoAI promoter activity in zinc-deficient Hep G2 cells. Thus zinc is critical in transcriptional regulation of apoAI gene expression in hepatocytes.

p53 protein and p21 mRNA levels and caspase-3 activity are altered by zinc status in aortic endothelial cells

The influence of zinc status on the levels of p53, as well as downstream targets of p53 in cell repair and survival, was examined in human aortic endothelial cells (HAECs). A serum-reduced low-zinc medium (ZD) was used to deplete zinc over one passage. Other treatments included zinc-normal control (ZN), zinc-adequate (ZA), and zinc-supplemented (ZS) treatment with 3.0, 16.0, and 32.0 microM zinc, respectively. Cellular zinc levels in the ZD cells were 64% of ZN controls; levels in the ZA cells were not different, but levels in ZS cells were significantly higher (40%) than in ZN cells. No difference in p53 mRNA abundance was detected among all treatments; however, p53 nuclear protein levels were >100% higher in the ZD and ZS cells and almost 200% higher in the ZA cells than in ZN controls. In addition, p21 mRNA abundance, a downstream target of p53 protein, was increased in the ZS cells compared with both the ZN control and ZD cells. In the ZS cells, bax and mcl-1 were also approximately 50% higher compared with ZN controls, whereas bcl-2 mRNA was increased compared with ZA cells. Moreover, caspase-3 activity of ZD cells was not different from that of ZN controls but was reduced to 83 and 69% of ZN controls in ZA and ZS cells, respectively. Thus p53 protein and p53 downstream target genes appeared to be modulated by intracellular zinc status in HAECs.

Metallothionein: early marker in the carcinogenesis of ulcerative colitis-associated colorectal carcinoma

Metallothioneins (MTs) are zinc-binding proteins whose overexpression may lead to sequestration of zinc ions and consequently to functional inactivation of the p53 tumor suppressor gene. The aim of the study was to investigate the potential role of MTs in the carcinogenesis of ulcerative colitis (UC) as well as possible effects on p53 function. The monoclonal antibodies E9 (anti-MT), DO-7, and 1801 (anti-p53) and the polyclonal antibody CM-1 (anti-p53) were used to stain formalin-fixed, paraffin-embedded colon specimens obtained from 14 patients with UC-associated colorectal carcinoma (CAC), 13 with high-grade dysplasia (HGD), 10 with low-grade dysplasia (LGD), and 30 with UC without dysplasia or carcinoma. Statistical significance (p <0.05) was assessed using Fisher's exact test. Positive MT staining (> 20% of tumor, dysplastic, or epithelial cells) was found in most UC and LGD but in only a small percentage of HGD and CAC (p <0.01 for CAC vs. UC and LGD vs. HGD). Positive p53 immunoreactivity was observed predominantly in HGD and CAC but not in LGD and UC (p <0.01 for CAC vs. UC and HGD vs. LGD). In histologically normal tissue neighboring CAC, significant MT expression was found in six of seven specimens with simultaneous lack of p53 expression. MT overexpression may represent an important early step in the development of CAC independent of p53 expression and should be investigated in the long term as an independent cancer risk factor in UC.

Zinc status affects p53, gadd45, and c-fos expression and caspase-3 activity in human bronchial epithelial cells

This study was designed to examine the influence of zinc depletion and supplementation on the expression of p53 gene, target genes of p53, and caspase-3 activity in normal human bronchial epithelial (NHBE) cells. A serum-free, low-zinc medium containing 0.4 micromol/l of zinc [zinc deficient (ZD)] was used to deplete cellular zinc over one passage. In addition, cells were cultured for one passage in media containing 4.0 micromol/l of zinc [zinc normal (ZN)], which represents normal culture concentrations (Clonetics); 16 micromol/l of zinc [zinc adequate (ZA)], which represents normal human plasma zinc levels; or 32 micromol/l of zinc [zinc supplemented (ZS)], which represents the high end of plasma zinc levels attainable by oral supplementation in humans. Compared with ZN cells, cellular zinc levels were 76% lower in ZD cells but 3.5-fold and 6-fold higher in ZA and ZS cells, respectively. Abundances of p53 mRNA and nuclear p53 protein were elevated in treatment groups compared with controls (ZN). For p53 mRNA abundance, the highest increase (3-fold) was observed in ZD cells. In contrast, the highest increase (17-fold) in p53 nuclear protein levels was detected in ZS cells. Moreover, gadd45 mRNA abundance was moderately elevated in ZD and ZA cells and was not altered in ZS cells compared with ZN cells. Furthermore, the only alteration in c-fos mRNA and caspase-3 activity was the twofold increase and the 25% reduction, respectively, detected in ZS compared with ZN cells. Thus p53, gadd45, and c-fos and caspase-3 activity appeared to be modulated by cellular zinc status in NHBE cells.

Tumor suppressor protein p53 mRNA and subcellular localization are altered by changes in cellular copper in human Hep G2 cells

Copper toxicity causes hepatic damage that can lead to the development of hepatocarcinoma. Similarly, copper deficiency has been reported to increase hepatocyte tumorigenesis. Thus, the objective of this work was to explore the role of copper toxicity and deficiency in the regulation of the tumor suppressor protein p53. Using Northern analysis, Western analysis, immunocytochemistry and the human hepatoma cell line Hep G2, this work showed that elevations in hepatocyte copper consistent with Wilson's disease (5.7-fold increase) induced p53 mRNA and confirmed that copper toxicity is correlated with apoptotic cell death. However, Western analysis and immunocytochemistry showed that post-transcriptional mechanisms are a significant part of the process, with p53 translocation from the cytosol into the nucleus of copper-treated cells. Treatment of Hep G2 cells with increasing concentrations of the copper chelator tetraethylenepentamine (TEPA, 0-50 micromol/L, 48 h) reduced cellular copper and increased mean p53 mRNA abundance by over fourfold with nuclear translocation of the wild-type protein. However, TEPA treatment did not result in a loss of cell viability or appear to induce apoptosis.

Retinol binding protein expression is induced in HepG2 cells by zinc deficiency

Zinc (Zn) deficiency is often associated with low plasma vitamin A (retinol) concentrations. It has been suggested that the reduction in plasma retinol is secondary to reduced liver retinol binding protein (RBP) synthesis. In the present study, RBP expression was determined in HepG2 cells cultured in either Zn adequate media or chelated media containing varying concentrations of Zn. Levels of RBP mRNA increased in a time- and Zn concentration-dependent manner such that 0.5 microM Zn-treated cells exhibited a >7.5-fold increase while cells treated with 15 microM Zn were increased 2.9-fold at 72 h compared to controls. RBP protein also progressively increased by 72 h to levels >8-fold and 3-fold higher than controls, in 0.5 microM and 15 microM Zn-treated cells, respectively. The increase in RBP occurred without any change in DNA concentration between groups through 72 h. The Zn deficiency-induced elevations in RBP transcript levels could be reversed within 24-48 h of repletion in Zn adequate media. Thus, the reductions in plasma retinol observed in Zn deficiency are in part a direct consequence of the deficiency.