Strategies for inducing and validating zinc deficiency and zinc repletion

Given the growing interest in the role of zinc in the onset and progression of diseases, there is a crucial demand for reliable methods to modulate zinc homeostasis. Using a dietary approach, we provide validated strategies to alter whole-body zinc in mice, applicable across species. For confirmation of zinc status, animal growth rates as well as plasma and urine zinc levels were evaluated. The accessible and cost-effective methodology outlined will increase scientific rigor, ensuring reproducibility in studies exploring the impact of zinc deficiency and repletion on the onset and progression of diseases.NEW & NOTEWORTHY This methods paper details dietary approaches to alter zinc homeostasis in rodents and qualitative and quantitative methods to ensure the zinc status of experimental animals. The outlined accessible and cost-effective protocol will elevate scientific rigor, ensuring reproducibility in studies exploring the impact of zinc deficiency and repletion on the onset and progression of a multitude of health conditions and diseases.

The transcription factor OsbZIP48 governs rice responses to zinc deficiency

Zinc (Zn) deficiency is the most prevalent micronutrient disorder in rice and leads to delayed development and decreased yield. Nevertheless, despite its primary importance, how rice responds to Zn deficiency remains poorly understood. This study presents genetic evidence supporting the crucial role of OsbZIP48 in regulating rice's response to Zn deficiency, consistent with earlier findings in the model plant Arabidopsis. Genetic inactivation of OsbZIP48 in rice seedlings resulted in heightened sensitivity to Zn deficiency and reduced Zn translocation from roots to shoots. Consistently, OsbZIP48 was constitutively expressed in roots, slightly induced by Zn deficiency in shoots and localized into nuclei induced by Zn deficiency. Comparative transcriptome analysis of the wild-type plants and osbzip48 mutant grown under Zn deficiency enabled the identification of OsbZIP48 target genes, including key Zn transporter genes (OsZIP4 and OsZIP8). We demonstrated that OsbZIP48 controlled the expressions of these genes by directly binding to their promoters, specifically to the Zn deficiency response element motif. This study establishes OsbZIP48 as a critical transcription factor in rice's response to Zn deficiency, offering valuable insights for developing Zn-biofortified rice varieties to combat global Zn limitation.

Lysosome-related organelles contain an expansion compartment that mediates delivery of zinc transporters to promote homeostasis

Zinc is an essential nutrient-it is stored during periods of excess to promote detoxification and released during periods of deficiency to sustain function. Lysosome-related organelles (LROs) are an evolutionarily conserved site of zinc storage, but mechanisms that control the directional zinc flow necessary for homeostasis are not well understood. In Caenorhabditis elegans intestinal cells, the CDF-2 transporter stores zinc in LROs during excess. Here, we identify ZIPT-2.3 as the transporter that releases zinc during deficiency; ZIPT-2.3 transports zinc, localizes to the membrane of LROs in intestinal cells, and is necessary for zinc release from LROs and survival during zinc deficiency. In zinc excess and deficiency, the expression levels of CDF-2 and ZIPT-2.3 are reciprocally regulated at the level of mRNA and protein, establishing a fundamental mechanism for directional flow to promote homeostasis. To elucidate how the ratio of CDF-2 and ZIPT-2.3 is altered, we used super-resolution microscopy to demonstrate that LROs are composed of a spherical acidified compartment and a hemispherical expansion compartment. The expansion compartment increases in volume during zinc excess and deficiency. These results identify the expansion compartment as an unexpected structural feature of LROs that facilitates rapid transitions in the composition of zinc transporters to mediate homeostasis, likely minimizing the disturbance to the acidified compartment.

Zinc acquisition and its contribution to Klebsiella pneumoniae virulence

Klebsiella pneumoniae is a World Health Organization priority pathogen and a significant clinical concern for infections of the respiratory and urinary tracts due to widespread and increasing resistance to antimicrobials. In the absence of a vaccine, there is an urgent need to identify novel targets for therapeutic development. Bacterial pathogens, including K. pneumoniae, require the d-block metal ion zinc as an essential micronutrient, which serves as a cofactor for ~6% of the proteome. During infection, zinc acquisition necessitates the use of high affinity uptake systems to overcome niche-specific zinc limitation and host-mediated nutritional immunity. Here, we report the identification of ZnuCBA and ZniCBA, two ATP-binding cassette permeases that are highly conserved in Klebsiella species and contribute to K. pneumoniae AJ218 zinc homeostasis, and the high-resolution structure of the zinc-recruiting solute-binding protein ZniA. The Znu and Zni permeases appear functionally redundant with abrogation of both systems required to reduce K. pneumoniae zinc accumulation. Disruption of both systems also exerted pleiotropic effects on the homeostasis of other d-block elements. Zinc limitation perturbed K. pneumoniae cell morphology and compromised resistance to stressors, such as salt and oxidative stress. The mutant strain lacking both systems showed significantly impaired virulence in acute lung infection models, highlighting the necessity of zinc acquisition in the virulence and pathogenicity of K. pneumoniae.

ZntA maintains zinc and cadmium homeostasis and promotes oxidative stress resistance and virulence in Vibrio parahaemolyticus

Although metals are essential for life, they are toxic to bacteria in excessive amounts. Therefore, the maintenance of metal homeostasis is critical for bacterial physiology and pathogenesis. Vibrio parahaemolyticus is a significant food-borne pathogen that mainly causes acute gastroenteritis in humans and acute hepatopancreatic necrosis disease in shrimp. Herein, we report that ZntA functions as a zinc (Zn) and cadmium (Cd) homeostasis mechanism and contributes to oxidative stress resistance and virulence in V. parahaemolyticus. zntA is remarkably induced by Zn, copper, cobalt, nickel (Ni), and Cd, while ZntA promotes V. parahaemolyticus growth under excess Zn/Ni and Cd conditions via maintaining Zn and Cd homeostasis, respectively. The growth of ΔzntA was inhibited under iron (Fe)-restricted conditions, and the inhibition was associated with Zn homeostasis disturbance. Ferrous iron supplementation improved the growth of ΔzntA under excess Zn, Ni or Cd conditions. The resistance of ΔzntA to H2O2-induced oxidative stress also decreased, and its virulence was attenuated in zebrafish models. Quantitative real-time PCR, mutagenesis, and β-galactosidase activity assays revealed that ZntR positively regulates zntA expression by binding to its promoter. Collectively, the ZntR-regulated ZntA is crucial for Zn and Cd homeostasis and contributes to oxidative stress resistance and virulence in V. parahaemolyticus.

CRISPR-screen identifies ZIP9 and dysregulated Zn2+ homeostasis as a cause of cancer-associated changes in glycosylation

INTRODUCTION

In epithelial cancers, truncated O-glycans, such as the Thomson-nouveau antigen (Tn) and its sialylated form (STn), are upregulated on the cell surface and associated with poor prognosis and immunological escape. Recent studies have shown that these carbohydrate epitopes facilitate cancer development and can be targeted therapeutically; however, the mechanism underpinning their expression remains unclear.

METHODS

To identify genes directly influencing the expression of cancer-associated O-glycans, we conducted an unbiased, positive-selection, whole-genome CRISPR knockout-screen using monoclonal antibodies against Tn and STn.

RESULTS AND CONCLUSIONS

We show that knockout of the Zn2+-transporter SLC39A9 (ZIP9), alongside the well-described targets C1GALT1 (C1GalT1) and its molecular chaperone, C1GALT1C1 (COSMC), results in surface-expression of cancer-associated O-glycans. No other gene perturbations were found to reliably induce O-glycan truncation. We furthermore show that ZIP9 knockout affects N-linked glycosylation, resulting in upregulation of oligo-mannose, hybrid-type, and α2,6-sialylated structures as well as downregulation of tri- and tetra-antennary structures. Finally, we demonstrate that accumulation of Zn2+ in the secretory pathway coincides with cell-surface presentation of truncated O-glycans in cancer tissue, and that over-expression of COSMC mitigates such changes. Collectively, the findings show that dysregulation of ZIP9 and Zn2+ induces cancer-like glycosylation on the cell surface by affecting the glycosylation machinery.

Transcriptional Response of Burkholderia cenocepacia H111 to Severe Zinc Starvation

Burkholderia cenocepacia is an opportunistic pathogen that is primarily associated with severe respiratory infections in people with cystic fibrosis. These bacteria have significant intrinsic resistance to antimicrobial therapy, and there is a need for more effective treatments. Bacterial zinc uptake and homeostasis systems are attractive targets for new drugs, yet our understanding of how bacteria acquire and utilise zinc remains incomplete. Here we have used RNA-sequencing and differential gene expression analysis to investigate how B. cenocepacia H111 is able to survive in zinc poor environments, such as those expected to be encountered within the host. The data shows that 201 genes are significantly differentially expressed when zinc supply is severely limited. Included in the 85 upregulated genes, are genes encoding a putative ZnuABC high affinity zinc importer, two TonB-dependent outer membrane receptors that may facilitate zinc uptake across the outer cell membrane, and a COG0523 family zinc metallochaperone. Amongst the 116 downregulated genes, are several zinc-dependent enzymes suggesting a mechanism of zinc sparring to reduce the cells demand for zinc when bioavailability is low.

A bioinformatic analysis of zinc transporters in intestinal Lactobacillaceae

As the second most abundant transition element and a crucial cofactor for many proteins, zinc is essential for the survival of all living organisms. To maintain required zinc levels and prevent toxic overload, cells and organisms have a collection of metal transport proteins for uptake and efflux of zinc. In bacteria, metal transport proteins are well defined for model organisms and many pathogens, but fewer studies have explored metal transport proteins, including those for zinc, in commensal bacteria from the gut microbiota. The healthy human gut microbiota comprises hundreds of species and among these, bacteria from the Lactobacillaceae family are well documented to have various beneficial effects on health. Furthermore, changes in dietary metal intake, such as for zinc and iron, are frequently correlated with changes in abundance of Lactobacillaceae. Few studies have explored zinc requirements and zinc homeostasis mechanisms in Lactobacillaceae, however. Here we applied a bioinformatics approach to identify and compare predicted zinc uptake and efflux proteins in several Lactobacillaceae genera of intestinal relevance. Few Lactobacillaceae had zinc transporters currently annotated in proteomes retrieved from the UniProt database, but protein sequence-based homology searches revealed that high-affinity ABC transporter genes are likely common, albeit with genus-specific domain features. P-type ATPase transporters are probably also common and some Lactobacillaceae genera code for predicted zinc efflux cation diffusion facilitators. This analysis confirms that Lactobacillaceae harbor genes for various zinc transporter homologs, and provides a foundation for systematic experimental studies to elucidate zinc homeostasis mechanisms in these bacteria.

Persistent and transient olfactory deficits in COVID-19 are associated to inflammation and zinc homeostasis

Introduction

The Coronavirus Disease 2019 (COVID-19) is mainly a respiratory syndrome that can affect multiple organ systems, causing a variety of symptoms. Among the most common and characteristic symptoms are deficits in smell and taste perception, which may last for weeks/months after COVID-19 diagnosis owing to mechanisms that are not fully elucidated.

Methods

In order to identify the determinants of olfactory symptom persistence, we obtained olfactory mucosa (OM) from 21 subjects, grouped according to clinical criteria: i) with persistent olfactory symptoms; ii) with transient olfactory symptoms; iii) without olfactory symptoms; and iv) non-COVID-19 controls. Cells from the olfactory mucosa were harvested for transcriptome analyses.

Results and discussion

RNA-Seq assays showed that gene expression levels are altered for a long time after infection. The expression profile of micro RNAs appeared significantly altered after infection, but no relationship with olfactory symptoms was found. On the other hand, patients with persistent olfactory deficits displayed increased levels of expression of genes involved in the inflammatory response and zinc homeostasis, suggesting an association with persistent or transient olfactory deficits in individuals who experienced SARS-CoV-2 infection.

Dihydroartemisinin Disrupts Zinc Homeostasis in Plasmodium falciparum To Potentiate Its Antimalarial Action via Pyknosis

Artemisinins have been used as first-line drugs worldwide to treat malaria caused by Plasmodium falciparum; however, its underlying mechanism is still unclear. This study aimed to identify the factors inducing growth inhibition via pyknosis, a state of intraerythrocytic developmental arrest, when exposing the parasite to dihydroartemisinin (DHA). Changes in the expression of genome-wide transcripts were assessed in the parasites treated with antimalarials, revealing the specific downregulation of zinc-associated proteins by DHA. The quantification of zinc levels in DHA-treated parasite indicated abnormal zinc depletion. Notably, the zinc-depleted condition in the parasite produced by a zinc chelator induced the generation of a pyknotic form and the suppression of its proliferation. The evaluation of the antimalarial activity of DHA or a glutathione-synthesis inhibitor in the zinc-depleted state showed that the disruption of zinc and glutathione homeostasis synergistically potentiated the growth inhibition of P. falciparum through pyknosis. These findings could help further understand the antimalarial actions of artemisinins for advancing malaria therapy.

Human cells experience a Zn2+ pulse in early G1

Zinc is an essential micronutrient required for all domains of life. Cells maintain zinc homeostasis using a network of transporters, buffers, and transcription factors. Zinc is required for mammalian cell proliferation, and zinc homeostasis is remodeled during the cell cycle, but whether labile zinc changes in naturally cycling cells has not been established. We use genetically encoded fluorescent reporters, long-term time-lapse imaging, and computational tools to track labile zinc over the cell cycle in response to changes in growth media zinc and knockdown of the zinc-regulatory transcription factor MTF-1. Cells experience a pulse of labile zinc in early G1, whose magnitude varies with zinc in growth media. Knockdown of MTF-1 increases labile zinc and the zinc pulse. Our results suggest that cells need a minimum zinc pulse to proliferate and that if labile zinc levels are too high, cells pause proliferation until labile cellular zinc is lowered.

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.

A conserved zinc-binding site in Acinetobacter baumannii PBP2 required for elongasome-directed bacterial cell shape

Acinetobacter baumannii is a gram-negative bacterial pathogen that causes challenging nosocomial infections. β-lactam targeting of penicillin-binding protein (PBP)-mediated cell wall peptidoglycan (PG) formation is a well-established antimicrobial strategy. Exposure to carbapenems or zinc (Zn)-deprived growth conditions leads to a rod-to-sphere morphological transition in A. baumannii, an effect resembling that caused by deficiency in the RodA-PBP2 PG synthesis complex required for cell wall elongation. While it is recognized that carbapenems preferentially acylate PBP2 in A. baumannii and therefore block the transpeptidase function of the RodA-PBP2 system, the molecular details underpinning cell wall elongation inhibition upon Zn starvation remain undefined. Here, we report the X-ray crystal structure of A. baumannii PBP2, revealing an unexpected Zn coordination site in the transpeptidase domain required for protein stability. Mutations in the Zn-binding site of PBP2 cause a loss of bacterial rod shape and increase susceptibility to β-lactams, therefore providing a direct rationale for cell wall shape maintenance and Zn homeostasis in A. baumannii. Furthermore, the Zn-coordinating residues are conserved in various β- and γ-proteobacterial PBP2 orthologs, consistent with a widespread Zn-binding requirement for function that has been previously unknown. Due to the emergence of resistance to virtually all marketed antibiotic classes, alternative or complementary antimicrobial strategies need to be explored. These findings offer a perspective for dual inhibition of Zn-dependent PG synthases and metallo-β-lactamases by metal chelating agents, considered the most sought-after adjuvants to restore β-lactam potency against gram-negative bacteria.

63Cu(I) binding to human kidney 68Zn7-βα MT1A: determination of Cu(I)-thiolate cluster domain specificity from ESI-MS and room temperature phosphorescence spectroscopy

Mammalian metallothioneins (MTs) are important proteins in Zn(II) and Cu(I) homeostasis with the Zn(II) and Cu(I) binding to the 20 cysteines in metal-thiolate clusters. Previous electrospray ionization (ESI) mass spectrometric (MS) analyses of Cu(I) binding to Zn7-MT were complicated by significant overlap of the natural abundance isotopic patterns for Zn(II) and Cu(I) leading to impossibly ambiguous stoichiometries. In this paper, isotopically pure 63Cu(I) and 68Zn(II) allowed determination of the specific stoichiometries in the 68 Zn,63Cu-βα MT1A species formed following the stepwise addition of 63Cu(I) to 68Zn7-βα MT1A. These species were characterized by ESI-MS and room temperature emission spectroscopy. The key species that form and their emission band centres are Zn5Cu5-βα MT1A (λ = 684 nm), Zn4Cu6-βα MT1A (λ = 750 nm), Zn3Cu9-βα MT1A (λ = 750 nm), Zn2Cu10-βα MT1A (λ = 750 nm), and Zn1Cu14-βα MT1A (λ = 634 nm). The specific domain stoichiometry of each species was determined by assessing the species forming following 63Cu(I) addition to the 68Zn3-β MT1A and 68Zn4-α MT1A domain fragments. The domain fragment emission suggests that Zn5Cu5-βα MT1A contains a Zn1Cu5-β cluster and the Zn4Cu6-βα MT1A, Zn3Cu9-βα MT1A, and Zn2Cu10-βα MT1A each contain a Cu6-β cluster. The species forming with >10 mol. eq. of 63Cu(I) in βα-MT1A exhibit emission from the Cu6-β cluster and an α domain cluster. This high emission intensity is seen at the end of the titrations of 68Zn7-βα MT1A and the 68Zn4-α MT1A domain fragment suggesting that the initial presence of the Zn(II) results in clustered Cu(I) binding in the α domain.

Zinc nutrition and dietary zinc supplements

As the second most abundant trace element in the human body, zinc nutrition is constantly a hot topic. More than one-third population is suffering zinc deficiency, which results in various types of diseases or nutritional deficiencies. Traditional ways of zinc supplementation seem with low absorption rates and significant side effects. Zinc supplements with dietary components are easily accessible and improve zinc utilization rate significantly. Also, mechanisms of maintaining zinc homeostasis are of broad interest. The present review focuses on zinc nutrition in human health in inductive methods. Mainly elaborate on different diseases relating to zinc disorder, highlighting the impact on the immune system and the recent COVID-19. Then raise food-derived zinc-binding compounds, including protein, peptide, polysaccharide, and polyphenol, and also analyze their possibilities to serve as zinc complementary. Finally, illustrate the way to maintain zinc homeostasis and the corresponding mechanisms. The review provides data information for maintaining zinc homeostasis with the food-derived matrix.

Fungal Zinc Homeostasis and Its Potential as an Antifungal Target: A Focus on the Human Pathogen Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic airborne fungus that causes severe invasive aspergillosis in immunocompromised patients. Zinc is an essential micronutrient for the growth of A. fumigatus and even for all microorganisms. An increasing number of studies have reported that fungal zinc acquisition ability plays a key role in fungal survival in hosts with an extremely zinc-limited microenvironment. The ability to fight scarcity and excess of zinc are tightly related to fungal virulence and may be used as new potential targets. Because the regulation of zinc homeostasis is important, a thorough understanding of the functional genes involved in the regulatory network for zinc homeostasis is required for fungal pathogens. The current mini-review summarized potential zinc homeostasis regulators in A. fumigatus and classified these regulators according to localization and function, which were identified or predicted based on A. fumigatus or deduced from homologs in model yeasts. Future perspectives for zinc homeostasis regulators as potential antifungal targets to treat invasive aspergillosis are also discussed.

Zinc in Human Health and Infectious Diseases

During the last few decades, the micronutrient zinc has proven to be an important metal ion for a well-functioning immune system, and thus also for a suitable immune defense. Nowadays, it is known that the main cause of zinc deficiency is malnutrition. In particular, vulnerable populations, such as the elderly in Western countries and children in developing countries, are often affected. However, sufficient zinc intake and homeostasis is essential for a healthy life, as it is known that zinc deficiency is associated with a multitude of immune disorders such as metabolic and chronic diseases, as well as infectious diseases such as respiratory infections, malaria, HIV, or tuberculosis. Moreover, the modulation of the proinflammatory immune response and oxidative stress is well described. The anti-inflammatory and antioxidant properties of zinc have been known for a long time, but are not comprehensively researched and understood yet. Therefore, this review highlights the current molecular mechanisms underlying the development of a pro-/ and anti-inflammatory immune response as a result of zinc deficiency and zinc supplementation. Additionally, we emphasize the potential of zinc as a preventive and therapeutic agent, alone or in combination with other strategies, that could ameliorate infectious diseases.

Therapeutic targeting of the USP2-E2F4 axis inhibits autophagic machinery essential for zinc homeostasis in cancer progression

Macroautophagy/autophagy is a conserved cellular process associated with tumorigenesis and aggressiveness, while mechanisms regulating expression of autophagic machinery genes in cancers still remain elusive. Herein, we identified E2F4 (E2F transcription factor 4) as a novel transcriptional activator of cytoprotective autophagy crucial for zinc homeostasis in cancer cells. Gain- and loss-of-function studies showed that E2F4 promoted autophagy in a cell cycle-dependent manner, resulting in facilitated degradation of MT (metallothionein) proteins, elevated distribution of Zn²⁺ within autophagosomes, decreased labile intracellular zinc ions, and increased growth, invasion, and metastasis of gastric cancer cells. Mechanistically, E2F4 directly regulated the transcription of ATG2A (autophagy related 2A) and ULK2 (unc-51 like autophagy activating kinase 2), leading to autophagic degradation of MT1E, MT1M, and MT1X, while USP2 (ubiquitin specific peptidase 2) stabilized E2F4 protein to induce its transactivation via physical interaction and deubiquitination in cancer cells. Rescue experiments revealed that USP2 harbored oncogenic properties via E2F4-facilitated autophagy and zinc homeostasis. Emetine, a small chemical inhibitor of autophagy, was able to block interaction between UPS2 and E2F4, increase labile intracellular zinc ions, and suppress tumorigenesis and aggressiveness. In clinical gastric cancer specimens, both USP2 and E2F4 were upregulated and associated with poor outcome of patients. These findings indicate that therapeutic targeting of the USP2-E2F4 axis inhibits autophagic machinery essential for zinc homeostasis in cancer progression.Abbreviations: 3-MA: 3-methyladenine; ANOVA: analysis of variance; ATG2A: autophagy related 2A; ATG5: autophagy related 5; ATP: adenosine triphosphate; BECN1: beclin 1; BiFC: bimolecular fluorescence complementation; CCND1: cyclin D1; CDK: cyclin dependent kinase; ChIP: chromatin immunoprecipitation; CHX: cycloheximide; Co-IP: co-immunoprecipitation; DAPI: 4',6-diamidino-2-phenylindole; E2F4: E2F transcription factor 4; eATP: extracellular adenosine triphosphate; EBSS: Earle's balanced salt solution; FP: first progression; FRET: fluorescence resonance energy transfer; FUCCI: fluorescent ubiquitination-based cell cycle indicator; GFP: green fluorescent protein; GST: glutathione S-transferase; HA: hemagglutinin; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MDM2: MDM2 proto-oncogene; MKI67/Ki-67: marker of proliferation Ki-67; MT: metallothionein; MT1E: metallothionein 1E; MT1M: metallothionein 1M; MT1X: metallothionein 1X; MTT: 3-(4,5-dimethyltriazol-2-yl)-2,5-diphenyl tetrazolium bromide; OS: overall survival; PECAM1/CD31: platelet and endothelial cell adhesion molecule 1; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; qPCR: quantitative PCR; RFP: red fluorescent protein; SQSTM1/p62: sequestosome 1; UBXN1: UBX domain protein 1; Ub: ubiquitin; ULK2: unc-51 like autophagy activating kinase 2; USP14: ubiquitin specific peptidase 14; USP2: ubiquitin specific peptidase 2; USP5: ubiquitin specific peptidase 5; USP7: ubiquitin specific peptidase 7; ZnCl₂: zinc chloride.

The Role of Zinc in GM-CSF-Induced Signaling in Human Polymorphonuclear Leukocytes

SCOPE

Zinc is suggested to be necessary for functional signaling induced by certain growth factors. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is a key factor for differentiation and activation of myeloid cells. This report analyses the impact of different zinc concentrations on GM-CSF-induced signaling in mature polymorphonuclear leukocytes (PMN).

METHODS AND RESULTS

As measured by flow cytometry, zinc increases surface GM-CSF receptor (GM-CSFR) in PMN, whereas monocytes respond with decreased GM-CSFR surface expression. Since total cellular GM-CSFR expression remains unaffected, the observed zinc-induced GM-CSFR surface dynamics may be explained by receptor redistribution. In PMN, zinc enhanced phosphorylation of mitogen-activated protein kinases (MAPK) in a dose-dependent manner as found in western blot. Zinc-induced MAPK phosphorylation is additionally augmented by moderate GM-CSF stimulation.

CONCLUSION

The present study demonstrates the opposing influence of zinc on GM-CSFR surface expression in monocytes and PMN. Zinc and GM-CSF, use in optimized concentrations, augment MAPK signaling, and increase expression of MAPK-induced myeloid cell leukemia-1 (Mcl-1) in PMN. Thus, this study concludes that zinc strengthens growth factor-induced signaling. Hence, the study provides a basis for further in vivo studies, focusing on the therapeutic value of zinc in patients with a disturbed GM-CSF signaling.

Zng1 is a GTP-dependent zinc transferase needed for activation of methionine aminopeptidase

The evolution of zinc (Zn) as a protein cofactor altered the functional landscape of biology, but dependency on Zn also created an Achilles' heel, necessitating adaptive mechanisms to ensure Zn availability to proteins. A debated strategy is whether metallochaperones exist to prioritize essential Zn-dependent proteins. Here, we present evidence for a conserved family of putative metal transferases in human and fungi, which interact with Zn-dependent methionine aminopeptidase type I (MetAP1/Map1p/Fma1). Deletion of the putative metal transferase in Saccharomyces cerevisiae (ZNG1; formerly YNR029c) leads to defective Map1p function and a Zn-deficiency growth defect. In vitro, Zng1p can transfer Zn2+ or Co2+ to apo-Map1p, but unlike characterized copper chaperones, transfer is dependent on GTP hydrolysis. Proteomics reveal mis-regulation of the Zap1p transcription factor regulon because of loss of ZNG1 and Map1p activity, suggesting that Zng1p is required to avoid a compounding effect of Map1p dysfunction on survival during Zn limitation.

Tryptophan regulates Drosophila zinc stores

SignificanceZinc deficiency in the human population, a major public health concern, can also be a consequence of nutritional deficiency in protein uptake. The discovery that tryptophan metabolites 3-hydroxykynurenine and xanthurenic acid are major zinc-binding ligands in insect cells establishes the kynurenine pathway as a regulator of systemic zinc homeostasis. Many biological processes influenced by zinc and the kynurenine pathway, including the regulation of innate and acquired immune responses to viral infections, have not been studied in light of the direct molecular links revealed in this study.

Zinc-Responsive Regulator Zur Regulates Zinc Homeostasis, Secondary Metabolism, and Morphological Differentiation in Streptomyces avermitilis

Zinc is an essential cofactor for many metal enzymes and transcription regulators. Zn²⁺ availability has long been known to affect antibiotic production and morphological differentiation of Streptomyces species. However, the molecular mechanism whereby zinc regulates these processes remains unclear. We investigated the regulatory roles of the zinc-sensing regulator Zur in Streptomyces avermitilis. Our findings demonstrate that Zur plays an essential role in maintaining zinc homeostasis by repressing the expression of the zinc uptake system ZnuACB and alternative non-zinc-binding ribosomal proteins and promoting the expression of zinc exporter ZitB. Deletion of the zur gene resulted in decreased production of avermectin and oligomycin and delayed morphological differentiation, and these parameters were restored close to wild-type levels in a zur-complemented strain. Zur bound specifically to Zur box in the promoter regions of avermectin pathway-specific activator gene aveR, oligomycin polyketide synthase gene olmA1, and filipin biosynthetic pathway-specific regulatory genes pteR and pteF. Analyses by reverse transcription quantitative PCR and luciferase reporter systems indicated that Zur directly activates the transcription of these genes, i.e., that Zur directly activates biosynthesis of avermectin and oligomycin. Zur positively regulated morphological development by repressing the transcription of differentiation-related genes ssgB and minD2. Our findings, taken together, demonstrate that Zur in S. avermitilis directly controls zinc homeostasis, biosynthesis of avermectin and oligomycin, and morphological differentiation. IMPORTANCE Biosynthesis of secondary metabolites and morphological differentiation in bacteria are affected by environmental signals. The molecular mechanisms whereby zinc availability affects secondary metabolism and morphological differentiation remain poorly understood. We identified several new target genes of the zinc response regulator Zur in Streptomyces avermitilis, the industrial producer of avermectin. Zur was found to directly and positively control avermectin production, oligomycin production, and morphological differentiation in response to extracellular Zn²⁺ levels. Our findings clarify the regulatory functions of Zur in Streptomyces, which involve linking environmental Zn²⁺ status with control of antibiotic biosynthetic pathways and morphological differentiation.

The Role of ZntA in Klebsiella pneumoniae Zinc Homeostasis

Klebsiella pneumoniae is an opportunistic Gram-negative pathogen that is a leading cause of healthcare-associated infections, including pneumonia, urinary tract infections, and sepsis. Essential to the colonization and infection by K. pneumoniae is the acquisition of nutrients, such as the transition metal ion zinc. Zinc has crucial structural and catalytic roles in the proteome of all organisms. Nevertheless, in excess, it has the potential to mediate significant toxicity by dysregulating the homeostasis of other transition elements, disrupting enzymatic processes, and perturbing metalloprotein cofactor acquisition. Here, we sought to elucidate the zinc detoxification mechanisms of K. pneumoniae, which remain poorly defined. Using the representative K. pneumoniae AJ218 strain, we showed that the P-type ATPase, ZntA, which is upregulated in response to cellular zinc stress, was the primary zinc efflux pathway. Deletion of zntA rendered K. pneumoniae AJ218 highly susceptible to exogenous zinc stress and manifested as an impaired growth phenotype and increased cellular accumulation of the metal. Loss of zntA also increased sensitivity to cadmium stress, indicating a role for this efflux pathway in cadmium resistance. Disruption of zinc homeostasis in the K. pneumoniae AJ218 ΔzntA strain also impacted manganese and iron homeostasis and was associated with increased production of biofilm. Collectively, this work showed the critical role of ZntA in K. pneumoniae zinc tolerance and provided a foundation for further studies on zinc homeostasis and the future development of novel antimicrobials to target this pathway. IMPORTANCE Klebsiella pneumoniae is a leading cause of healthcare-associated infections, including pneumonia, urinary tract infections, and sepsis. Treatment of K. pneumoniae infections is becoming increasingly challenging due to high levels of antibiotic resistance and the rising prevalence of carbapenem-resistant, extended-spectrum β-lactamases producing strains. Zinc is essential to the colonization and infection by many bacterial pathogens but toxic in excess. This work described the first dissection of the pathways associated with resisting extracellular zinc stress in K. pneumoniae. This study revealed that the P-type ATPase ZntA was highly upregulated in response to exogenous zinc stress and played a major role in maintaining bacterial metal homeostasis. Knowledge of how this major bacterial pathogen resists zinc stress provided a foundation for antimicrobial development studies to target and abrogate their essential function.

Zinc homeostasis in immunity and its association with preterm births

Preterm birth is among the most common adverse pregnancy outcomes and is the leading cause of neonatal mortality and morbidity. While trace elements are essential for humans, their specific roles in the prenatal period remain unexplored. Zinc, a ubiquitous element plays a pivotal role in protein synthesis, cell division, nucleic acid metabolism, apoptosis, ageing, reproduction, immunological as well as antioxidant defense mechanism. Although zinc quantities are very small in body tissue, it is involved in every conceivable biochemical pathway which is critical for the performance of various functions necessary to sustain life. Owing to the multifactorial role of zinc, it is not possible to attribute a certain zinc dependent mechanism in pre-term births. Although the effect of zinc deficiency on immunity, its impact on maternal function and health as well as its role in the developing foetus is well documented, much less attention has been given to the understanding of micronutrient zinc homeostasis in immunity and its association with preterm births. Despite extensive research, the pathway by which zinc regulates pregnancy outcomes as well as the function of immune cells in controlling the delivery status (term/ preterm) is still obscure. The present review aims to focus on the understanding of relationship of micronutrient zinc homeostasis in immunity and its association with preterm births.

Metal transporter Slc30a1 controls pharyngeal neural crest differentiation via the zinc-Snai2-Jag1 cascade

The pharyngeal arch (PA) is a neural crest (NC)-derived organ that is transiently developed during embryogenesis and is required for the subsequent development of various tissues. However, the role of zinc during PA differentiation from NC progenitor cells is unknown. Here, we found that the metal transporters Slc30a1a and Slc30a1b mediate zinc homeostasis during PA differentiation. Slc30a1-deficient zebrafish develop zinc accumulation in NC cells, with increased expression of stemness markers and PA dorsal genes, and SMART-seq analyses revealed that the genes snai2 and jag1b may serve as downstream targets. Furthermore, functional studies showed that knocking down either snai2 or jag1b rescues PA development in Slc30a1-deficient zebrafish. Notably, we identified the double zinc-finger domain in the transcription factor Snai2 as a zinc-responsive element that regulates jag1b expression. Our findings indicate that the Slc30a1/zinc-snai2-jag1b axis is an essential regulatory network controlling PA differentiation, shedding new light on the function of zinc homeostasis in maintaining NC cell stemness and multipotency in vertebrates.

Intracellular zinc during cell activation and zinc deficiency

INTRODUCTION

Zinc is an essential trace element having manifold functions within living cells. Zinc deficiency but also zinc excess impairs cell-specific functions whereas a balanced zinc level is required for an adequate cell behavior.

MATERIAL AND METHODS

This study deals with the impact of cellular priming due to stimulation with interleukin (IL)-1, IL-2, IL-4, IL-6 or the chemokine CXCL12a and its subsequent influence on the intracellular free zinc concentration. Since cellular priming and activation is essential for proper immunological reactions, and across that highly cell-type specific, we investigated T cells, B cells, and peripheral blood mononuclear cells (PBMCs). Additionally, alterations of the intracellular zinc content was investigated by inducing zinc deficiency using the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine (TPEN) with subsequent re-supplementation of zinc, hence generating an intracellular zinc flux. Evaluation of zinc staining with FluoZin3-AM, Zinpyr-1 and Zinquin was done by flow cytometry or by fluorescence microscopy.

RESULTS

Our results indicate that cellular priming for different periods of time (10 minutes/one hour) causes decreased intracellular free zinc concentrations in the FluoZin3-AM staining and increased zinc concentrations stained with Zinpyr-1. Furthermore, zinc supplementation after induced zinc deficiency leads to a fast and excessive rise of the intracellular free zinc levels in most cellular compartments.

CONCLUSION

Our study emphasizes the importance of zinc homeostasis and zinc distribution during cellular priming and for certain signaling cascades especially in T and B cells. Moreover, we demonstrated that zinc re-supplementation of zinc deficient cells results in significantly elevated intracellular free zinc concentrations compared to untreated controls. Hence, this underlines the need of a balanced zinc homeostasis for proper immune cell function.

Slc39a2-Mediated Zinc Homeostasis Modulates Innate Immune Signaling in Phenylephrine-Induced Cardiomyocyte Hypertrophy

Zinc dyshomeostasis has been involved in the pathogenesis of cardiac hypertrophy; however, the dynamic regulation of intracellular zinc and its downstream signaling in cardiac hypertrophy remain largely unknown. Using Zincpyr1 staining, we found a significant decrease of intracellular Zinc concentration in phenylephrine (PE)-induced hypertrophy of neonatal rat ventricular myocytes (NRVMs). We then screened SLC39 family members responsible for zinc uptake and identified Slc39a2 as the only one altered by PE treatment. Slc39a2 knockdown in NRVMs reduced the intracellular Zinc level, and exacerbated the hypertrophic responses to PE treatment. In contrast, adenovirus-mediated Slc39a2 overexpression enhanced zinc uptake and suppressed PE-induced Nppb expression. RNA sequencing analysis showed a pro-hypertrophic transcriptome reprogramming after Slc39a2 knockdown. Interestingly, the innate immune signaling pathways, including NOD signaling, TOLL-like receptor, NFκB, and IRFs, were remarkably enriched in the Slc39a2-regulated genes. Slc39a2 deficiency enhanced the phosphorylation of P65 NFκB and STAT3, and reduced the expression of IκBα. Finally, the expression of IRF7 was significantly increased by Slc39a2 knockdown, which was in turn suppressed by IRF7 knockdown. Our data demonstrate that zinc homeostasis mediated by a Slc39a2/IRF7 regulatory circuit contributes to the alteration of innate immune signaling in cardiomyocyte hypertrophy.

Redundant roles of four ZIP family members in zinc homeostasis and seed development in Arabidopsis thaliana

Zinc (Zn) is essential for normal plant growth and development. The Zn-regulated transporter, iron-regulated transporter (IRT)-like protein (ZIP) family members are involved in Zn transport and cellular Zn homeostasis throughout the domains of life. In this study, we have characterized four ZIP transporters from Arabidopsis thaliana (IRT3, ZIP4, ZIP6, and ZIP9) to better understand their functional roles. The four ZIP proteins can restore the growth defect of a yeast Zn uptake mutant and are upregulated under Zn deficiency. Single and double mutants show no phenotypes under Zn-sufficient or Zn-limited growth conditions. In contrast, triple and quadruple mutants show impaired growth irrespective of external Zn supply due to reduced Zn translocation from root to shoot. All four ZIP genes are highly expressed during seed development, and siliques from all single and higher-order mutants exhibited an increased number of abnormal seeds and decreased Zn levels in mature seeds relative to wild type. The seed phenotypes could be reversed by supplementing the soil with Zn. Our data demonstrate that IRT3, ZIP4, ZIP6, and ZIP9 function redundantly in maintaining Zn homeostasis and seed development in A. thaliana.

Cadmium hijacks the high zinc response by binding and activating the HIZR-1 nuclear receptor

Cadmium is an environmental pollutant and significant health hazard that is similar to the physiological metal zinc. In Caenorhabditis elegans, high zinc homeostasis is regulated by the high zinc activated nuclear receptor (HIZR-1) transcription factor. To define relationships between the responses to high zinc and cadmium, we analyzed transcription. Many genes were activated by both high zinc and cadmium, and hizr-1 was necessary for activation of a subset of these genes; in addition, many genes activated by cadmium did not require hizr-1, indicating there are at least two mechanisms of cadmium-regulated transcription. Cadmium directly bound HIZR-1, promoted nuclear accumulation of HIZR-1 in intestinal cells, and activated HIZR-1-mediated transcription via the high zinc activation (HZA) enhancer. Thus, cadmium binding promotes HIZR-1 activity, indicating that cadmium acts as a zinc mimetic to hijack the high zinc response. To elucidate the relationships between high zinc and cadmium detoxification, we analyzed genes that function in three pathways: the pcs-1/phytochelatin pathway strongly promoted cadmium resistance but not high zinc resistance, the hizr-1/HZA pathway strongly promoted high zinc resistance but not cadmium resistance, and the mek-1/sek-1/kinase signaling pathway promoted resistance to high zinc and cadmium. These studies identify resistance pathways that are specific for high zinc and cadmium, as well as a shared pathway.

The Effects of Essential and Non-Essential Metal Toxicity in the Drosophila melanogaster Insect Model: A Review

The biological effects of environmental metal contamination are important issues in an industrialized, resource-dependent world. Different metals have different roles in biology and can be classified as essential if they are required by a living organism (e.g., as cofactors), or as non-essential metals if they are not. While essential metal ions have been well studied in many eukaryotic species, less is known about the effects of non-essential metals, even though essential and non-essential metals are often chemically similar and can bind to the same biological ligands. Insects are often exposed to a variety of contaminated environments and associated essential and non-essential metal toxicity, but many questions regarding their response to toxicity remain unanswered. Drosophila melanogaster is an excellent insect model species in which to study the effects of toxic metal due to the extensive experimental and genetic resources available for this species. Here, we review the current understanding of the impact of a suite of essential and non-essential metals (Cu, Fe, Zn, Hg, Pb, Cd, and Ni) on the D. melanogaster metal response system, highlighting the knowledge gaps between essential and non-essential metals in D. melanogaster. This review emphasizes the need to use multiple metals, multiple genetic backgrounds, and both sexes in future studies to help guide future research towards better understanding the effects of metal contamination in general.

Zinc dyshomeostasis in azoxymethane-induced colonic precancerous and cancerous lesions in Fischer rats

Zinc is an essential micronutrient involved in various biological processes. It is also argued that tumors need zinc for maintenance and proliferation and tumor cell apoptosis. Zinc homeostasis is regulated by the gastrointestinal tract and involves interplay of host, dietary, environmental and social factors such as alcohol consumption. The DNA alkylation agent azoxymethane (AOM), which is primarily activated in the liver, induces a high incidence of initiation and promotion steps of precancerous lesions in the colon of rats. The altered expression of hepatic zinc transporters by AOM may lead to zinc dyshomeostasis in liver. Decreased serum zinc concentration, despite increased liver zinc also indicates altered liver zinc mobilization and failure to regulate zinc homeostasis. During the transformation from normal colonic mucosa to colonic epithelial hyperplasia and aberrant crypt formation, a reduction in zinc concentration is observed. It will be interesting to study further if the same trend continues throughout tumor progression towards adenocarcinomas. Lowered local zinc concentrations in the colon epithelium may not just reflect a bystander effect, but may induce cell proliferation and compromise DNA integrity due to impairment of zinc-containing proteins. In congruence with the tissue zinc concentrations, metallothionein levels were found to be less induced in AOM -administered colon compared to normal healthy colon. Lowered tissue zinc levels in small and large intestine were also associated with increased expression of mRNA and protein ZnT1. In this regard, the mode of zinc responsiveness to ZnT1 mimics that of metallothionein, albeit at a lower level for ZnT1.

Insights Into Histoplasma capsulatum Behavior on Zinc Deprivation

Histoplasma capsulatum is a thermodimorphic fungus that causes histoplasmosis, a mycosis of global incidence. The disease is prevalent in temperate and tropical regions such as North America, South America, Europe, and Asia. It is known that during infection macrophages restrict Zn availability to H. capsulatum as a microbicidal mechanism. In this way the present work aimed to study the response of H. capsulatum to zinc deprivation. In silico analyses showed that H. capsulatum has eight genes related to zinc homeostasis ranging from transcription factors to CDF and ZIP family transporters. The transcriptional levels of ZAP1, ZRT1, and ZRT2 were induced under zinc-limiting conditions. The decrease in Zn availability increases fungicidal macrophage activity. Proteomics analysis during zinc deprivation at 24 and 48 h showed 265 proteins differentially expressed at 24 h and 68 at 48 h. Proteins related to energy production pathways, oxidative stress, and cell wall remodeling were regulated. The data also suggested that low metal availability increases the chitin and glycan content in fungal cell wall that results in smoother cell surface. Metal restriction also induces oxidative stress triggered, at least in part, by reduction in pyridoxin synthesis.

Zinc at the Host-Fungus Interface: How to Uptake the Metal?

Zinc is an essential nutrient for all living organisms. However, firm regulation must be maintained since micronutrients also can be toxic in high concentrations. This notion is reinforced when we look at mechanisms deployed by our immune system, such as the use of chelators or membrane transporters that capture zinc, when threatened with pathogens, like fungi. Pathogenic fungi, on the other hand, also make use of a variety of transporters and specialized zinc captors to survive these changes. In this review, we sought to explain the mechanisms, grounded in experimental analysis and described to date, utilized by pathogenic fungi to maintain optimal zinc levels.

Direct and Indirect Inhibition of Salmonella Peptide Deformylase by Nitric Oxide

We have previously shown that the host-derived antimicrobial mediator nitric oxide (NO·) mobilizes zinc from bacterial metalloproteins. The present study demonstrates that NO· inactivates the essential iron-containing enzyme peptide deformylase, both by promoting its mismetallation by zinc and by directly modifying its metal-binding site. We explain how free intracellular zinc is detrimental for cells and reveal a new mechanism of NO·-mediated bacterial growth inhibition that is distinct from previously known targets.

Salmonella enterica serovar Typhimurium is an intracellular pathogen that elicits nitric oxide (NO·) production by host macrophages. NO· is a potent antimicrobial mediator with diverse targets, including protein thiols and metal centers. The mobilization of zinc from metalloproteins by NO· increases the availability of free intracellular zinc, which is detrimental to bacterial cells, but the precise mechanism of zinc cytotoxicity is uncertain. Here, we show that excess zinc results in the mismetallation of the essential iron-containing enzyme peptide deformylase (PDF), thereby diminishing its activity. PDF mismetallation is observed in zinc-treated bacteria lacking the zinc exporters ZntA and ZitB and is also observed during nitrosative stress, suggesting that NO·-mediated zinc mobilization results in PDF mismetallation. However, NO· also inhibits PDF directly by S-nitrosylating the metal-binding Cys90 residue. These observations identify PDF as an essential bacterial protein that is subject to both direct and indirect inactivation by NO·, providing a novel mechanism of zinc toxicity and NO·-mediated antibacterial activity.

Slc39a5-mediated zinc homeostasis plays an essential role in venous angiogenesis in zebrafish

Angiogenesis is a precise process mediated by a variety of signals and the environmental niche. Although the essential trace element zinc and its homeostasis are essential for maintaining proper cellular functions, whether zinc plays a role in angiogenesis is currently unknown. Using zebrafish embryos as a model system, we found that zinc treatment significantly increased the expression of the slc39a5 gene, which encodes the zinc transporter Slc39a5. Moreover, knocking down slc39a5 expression using either a morpholino or CRISPR/Cas9-mediated gene editing led to cardiac ischaemia and an accumulation of red blood cells in the caudal vein plexus (CVP), as well as delayed venous sprouting and fewer vascular loops in the CVP region during early development. Further analysis revealed significantly reduced proliferation and delayed cell migration in the caudal vein of slc39a5 morphants. At the mechanistic level, we found increased levels of systemic zinc in slc39a5-deficient embryos, and chelating zinc restored CVP development. In addition, we found that zinc overload in wild-type embryos leads to impaired CVP formation. Taken together, these results indicate that Slc39a5 plays a critical role in endothelial sprouting and migration in venous angiogenesis by regulating zinc homeostasis.

Zinc Deficiency Disturbs Mucin Expression, O-Glycosylation and Secretion by Intestinal Goblet Cells

Approximately 1 billion people worldwide suffer from zinc deficiency, with severe consequences for their well-being, such as critically impaired intestinal health. In addition to an extreme degeneration of the intestinal epithelium, the intestinal mucus is seriously disturbed in zinc-deficient (ZD) animals. The underlying cellular processes as well as the relevance of zinc for the mucin-producing goblet cells, however, remain unknown. To this end, this study examines the impact of zinc deficiency on the synthesis, production, and secretion of intestinal mucins as well as on the zinc homeostasis of goblet cells using the in vitro goblet cell model HT-29-MTX. Zinc deprivation reduced their cellular zinc content, changed expression of the intestinal zinc transporters ZIP-4, ZIP-5, and ZnT1 and increased their zinc absorption ability, outlining the regulatory mechanisms of zinc homeostasis in goblet cells. Synthesis and secretion of mucins were severely disturbed during zinc deficiency, affecting both MUC2 and MUC5AC mRNA expression with ongoing cell differentiation. A lack of zinc perturbed mucin synthesis predominantly on the post-translational level, as ZD cells produced shorter O-glycans and the main O-glycan pattern was shifted in favor of core-3-based mucins. The expression of glycosyltransferases that determine the formation of core 1-4 O-glycans was altered in zinc deficiency. In particular, B3GNT6 mRNA catalyzing core 3 formation was elevated and C2GNT1 and C2GNT3 elongating core 1 were downregulated in ZD cells. These novel insights into the molecular mechanisms impairing intestinal mucus stability during zinc deficiency demonstrate the essentiality of zinc for the formation and maintenance of this physical barrier.

Critical Role of Zur and SmtB in Zinc Homeostasis of Mycobacterium smegmatis

Zinc homeostasis is crucial for bacterial cells, since imbalances affect viability. However, in mycobacteria, knowledge of zinc metabolism is incomplete. Mycobacterium smegmatis (MSMEG) is an environmental, nonpathogenic Mycobacterium that is widely used as a model organism to study mycobacterial metabolism and pathogenicity. How MSMEG maintains zinc homeostasis is largely unknown. SmtB and Zur are important regulators of bacterial zinc metabolism. In mycobacteria, these regulators are encoded by an operon, whereas in other bacterial species, SmtB and Zur are encoded on separate loci. Here, we show that the smtB-zur operon is consistently present within the genus Mycobacterium but otherwise found only in Nocardia, Saccharothrix, and Corynebacterium diphtheriae By RNA deep sequencing, we determined the Zur and SmtB regulons of MSMEG and compared them with transcriptional responses after zinc starvation or excess. We found an exceptional genomic clustering of genes whose expression was strongly induced by zur deletion and zinc starvation. These genes encoded zinc importers such as ZnuABC and three additional putative zinc transporters, including the porin MspD, as well as alternative ribosomal proteins. In contrast, only a few genes were affected by deletion of smtB and zinc excess. The zinc exporter ZitA was most prominently regulated by SmtB. Moreover, transcriptional analyses in combination with promoter and chromatin immunoprecipitation assays revealed a special regulation of the smtB-zur operon itself: an apparently zinc-independent, constitutive expression of smtB-zur resulted from sensitive coregulation by both SmtB and Zur. Overall, our data revealed yet unknown peculiarities of mycobacterial zinc homeostasis.IMPORTANCE Zinc is crucial for many biological processes, as it is an essential cofactor of enzymes and a structural component of regulatory and DNA binding proteins. Hence, all living cells require zinc to maintain constant intracellular levels. However, in excess, zinc is toxic. Therefore, cellular zinc homeostasis needs to be tightly controlled. In bacteria, this is achieved by transcriptional regulators whose activity is mediated via zinc-dependent conformational changes promoting or preventing their binding to DNA. SmtB and Zur are important antagonistically acting bacterial regulators in mycobacteria. They sense changes in zinc concentrations in the femtomolar range and regulate transcription of genes for zinc acquisition, storage, and export. Here, we analyzed the role of SmtB and Zur in zinc homeostasis in Mycobacterium smegmatis Our results revealed novel insights into the transcriptional processes of zinc homeostasis in mycobacteria and their regulation.

A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models

Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.

ZafA-mediated regulation of zinc homeostasis is required for virulence in the plant pathogen Fusarium oxysporum

During infection, soilborne fungal pathogens face limiting conditions of different metal ions, including zinc. The role of zinc homeostasis in fungal pathogenicity on plants remains poorly understood. Here it is shown that the transcription factor ZafA, orthologous to Saccharomyces cerevisiae Zap1, functions as a key regulator of zinc homeostasis and virulence in Fusarium oxysporum, a cross-kingdom pathogen that causes vascular wilt on more than 100 plant species and opportunistic infections in humans. Expression of zafA is induced under zinc-limiting conditions and repressed by zinc. Interestingly, zafA is markedly up-regulated during early stages of plant infection, suggesting that F. oxysporum must cope with limited availability of zinc. Deletion of zafA results in deactivation of high-affinity zinc transporters, leading to impaired growth under zinc deficiency. Fusarium oxysporum strains lacking ZafA are reduced in their capability to invade and kill tomato plants and the non-vertebrate animal model Galleria mellonella. Collectively, the results indicate that ZafA-mediated adaptation to zinc deficiency is required for full virulence of F. oxysporum on plant and animal hosts.

Zinc dysregulation in cancers and its potential as a therapeutic target

Zinc is an essential element and serves as a structural or catalytic component in many proteins. Two families of transporters are involved in maintaining cellular zinc homeostasis: the ZIP (SLC39A) family that facilitates zinc influx into the cytoplasm, and the ZnT (SLC30A) family that facilitates zinc efflux from the cytoplasm. Zinc dyshomeostasis caused by the dysfunction of zinc transporters can contribute to the initiation or progression of various cancers, including prostate cancer, breast cancer, and pancreatic cancer. In addition, intracellular zinc fluctuations lead to the disturbance of certain signaling pathways involved in the malignant properties of cancer cells. This review briefly summarizes our current understanding of zinc dyshomeostasis in cancer, and discusses the potential roles of zinc or zinc transporters in cancer therapy.

Upregulation of ZIP14 and Altered Zinc Homeostasis in Muscles in Pancreatic Cancer Cachexia

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer type in which the mortality rate approaches the incidence rate. More than 85% of PDAC patients experience a profound loss of muscle mass and function, known as cachexia. PDAC patients with this condition suffer from decreased tolerance to anti-cancer therapies and often succumb to premature death due to respiratory and cardiac muscle wasting. Yet, there are no approved therapies available to alleviate cachexia. We previously found that upregulation of the metal ion transporter, Zip14, and altered zinc homeostasis are critical mediators of cachexia in metastatic colon, lung, and breast cancer models. Here, we show that a similar mechanism is likely driving the development of cachexia in PDAC. In two independent experimental metastasis models generated from the murine PDAC cell lines, Pan02 and FC1242, we observed aberrant Zip14 expression and increased zinc ion levels in cachectic muscles. Moreover, in advanced PDAC patients, high levels of ZIP14 in muscles correlated with the presence of cachexia. These studies underscore the importance of altered ZIP14 function in PDAC-associated cachexia development and highlight a potential therapeutic opportunity for improving the quality of life and prolonging survival in PDAC patients.

SlZRT2 Encodes a ZIP Family Zn Transporter With Dual Localization in the Ectomycorrhizal Fungus Suillus luteus

Ectomycorrhizal (ECM) fungi are important root symbionts of trees, as they can have significant effects on the nutrient status of plants. In polluted environments, particular ECM fungi can protect their host tree from Zn toxicity by restricting the transfer of Zn while securing supply of essential nutrients. However, mechanisms and regulation of cellular Zn homeostasis in ECM fungi are largely unknown, and it remains unclear how ECM fungi affect the Zn status of their host plants. This study focuses on the characterization of a ZIP (Zrt/IrtT-like protein) transporter, SlZRT2, in the ECM fungus Suillus luteus, a common root symbiont of young pine trees. SlZRT2 is predicted to encode a plasma membrane-located Zn importer. Heterologous expression of SlZRT2 in yeast mutants with impaired Zn uptake resulted in a minor impact on cellular Zn accumulation and growth. The SlZRT2 gene product showed a dual localization and was detected at the plasma membrane and perinuclear region. S. luteus ZIP-family Zn uptake transporters did not show the potential to induce trehalase activity in yeast and to function as Zn sensors. In response to excess environmental Zn, gene expression analysis demonstrated a rapid but minor and transient decrease in SlZRT2 transcript level. In ECM root tips, the gene is upregulated. Whether this regulation is due to limited Zn availability at the fungal-plant interface or to developmental processes is unclear. Altogether, our results suggest a function for SlZRT2 in cellular Zn redistribution from the ER next to a putative role in Zn uptake in S. luteus.

Zinc Absorption and Endogenous Fecal Zinc Losses in Bangladeshi Toddlers at Risk for Environmental Enteric Dysfunction

OBJECTIVES

Environmental enteric dysfunction (EED) impairs zinc absorption from food, and zinc deficiency may contribute to the poor growth associated with EED. We examined zinc absorption from a standardized aqueous zinc dose, and habitual daily endogenous fecal zinc excretion (EFZ) and compared these outcomes between children grouped by the lactulose to mannitol ratio (L:M).

METHODS

Bangladeshi toddlers (18-24 months) with low (<0.09) and high (≥0.09) L:M were administered isotope-labeled 3 mg aqueous zinc in the fasted state. Fractional absorption of zinc (FAZ) and EFZ were measured by dual stable isotope tracer method and an isotope dilution method, respectively. Secondary aims included examining relationships of biomarkers of systemic and intestinal inflammation and gut function with FAZ and EFZ.

RESULTS

Forty children completed the study; nearly all had evidence of EED. No differences in zinc homeostasis measurements (mean ± SD) were observed between high and low L:M groups: FAZ was 0.38 ± 0.19 and 0.31 ± 0.19, respectively; both figures were within estimated reference range. Means of EFZ were 0.73 ± 0.27 and 0.76 ± 0.20 mg/day for high and low L:M, respectively, and were 10% to 15% above estimated reference range. Regression analyses indicated that biomarkers of systemic inflammation were directly associated with increasing FAZ, consistent with increased gut permeability. Biomarkers of intestinal inflammation were negatively associated with EFZ, consistent with low-zinc intake and chronic deficiency.

CONCLUSIONS

In these children at risk of EED, endogenous zinc losses were not markedly increased. Results suggest that efforts to improve zinc status in EED should focus on substantially improving zinc intakes.

Zinc and Iron Homeostasis: Target-Based Drug Screening as New Route for Antifungal Drug Development

The incidence of fungal diseases is on the rise and the number of fatalities is still unacceptably high. While advances into antifungal drug development have been made there remains an urgent need to develop novel antifungal agents targeting as-yet unexploited pathways, such as metal ion homeostasis. Here we report such an approach by developing a metal sensor screen in the opportunistic human fungal pathogen Candida albicans. Using this reporter strain, we screened a library of 1,200 compounds and discovered several active compounds not previously described as chemical entities with antifungal properties. Two of these, artemisinin and pyrvinium pamoate, have been further characterized and their interference with metal homeostasis and potential as novel antifungal compounds validated. Lastly, we demonstrate that the same strain can be used to report on intracellular conditions within host phagocytes, paving the way toward the development of novel screening platforms that could identify compounds with the potential to perturb ion homeostasis of the pathogen specifically within host cells.

Identification, Functional Characterization, and Regulon Prediction of the Zinc Uptake Regulator (zur) of Bacillus anthracis - An Insight Into the Zinc Homeostasis of the Pathogen

Zinc has an abounding occurrence in the prokaryotes and plays paramount roles including catalytic, structural, and regulatory. Zinc uptake regulator (Zur), a Fur family transcriptional regulator, is connoted in maintaining zinc homeostasis in the pathogenic bacteria by binding to zinc and regulating the genes involved in zinc uptake and mobilization. Zinc homeostasis has been marginally scrutinized in Bacillus anthracis, the top-rated bio-terror agent, with no decipherment of the role of Zur. Of the three Fur family regulators in B. anthracis, BAS4181 is annotated as a zinc-specific transcriptional regulator. This annotation was further substantiated by our stringent computational and experimental analyses. The residues critical for zinc and DNA binding were delineated by homology modeling and sequence/structure analysis. ba zur existed as a part of a three-gene operon. Purified BaZur prodigiously existed in the dimeric form, indicated by size exclusion chromatography and blue native-polyacrylamide gel electrophoresis (PAGE). Computational and manual strategies were employed to decipher the putative regulon of ba zur, comprising of 11 genes, controlled by six promoters, each harboring at least one Zur box. The DNA binding capability of the purified BaZur to the upstream regions of the ba zur operon, yciC, rpmG, znuA, and genes encoding a GTPase cobalamine synthesis protein and a permease was ascertained by electrophoretic mobility shift assays. The regulon genes, implicated in zinc uptake and mobilization, were mostly negatively regulated by BaZur. The ba zur expression was downregulated upon exposure of cells to an excess of zinc. Conversely, it exhibited a marked upregulation under N, N, N', N'-Tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) mediated zinc-depleted environment, adding credence to its negative autoregulation. Moreover, an increase in the transcript levels of the regulon genes znuA, rpmG, and yciC upon exposure of cells to TPEN connoted their role in combating hypo-zincemic conditions by bringing about zinc uptake and mobilization. Thus, this study functionally characterizes Zur of B. anthracis and elucidates its role in maintaining zinc homeostasis.

Tuning site-specific dynamics to drive allosteric activation in a pneumococcal zinc uptake regulator

MarR (multiple antibiotic resistance repressor) family proteins are bacterial repressors that regulate transcription in response to a wide range of chemical signals. Although specific features of MarR family function have been described, the role of atomic motions in MarRs remains unexplored thus limiting insights into the evolution of allostery in this ubiquitous family of repressors. Here, we provide the first experimental evidence that internal dynamics play a crucial functional role in MarR proteins. Streptococcus pneumoniae AdcR (adhesin-competence repressor) regulates Zn^II homeostasis and Zn^II functions as an allosteric activator of DNA binding. Zn^II coordination triggers a transition from somewhat independent domains to a more compact structure. We identify residues that impact allosteric activation on the basis of Zn^II-induced perturbations of atomic motions over a wide range of timescales. These findings appear to reconcile the distinct allosteric mechanisms proposed for other MarRs and highlight the importance of conformational dynamics in biological regulation.

Transcriptome analysis reveals an altered expression profile of zinc transporters in colorectal cancer

Zinc is a transition metal and catalytic cofactor involved in many biological processes including proliferation, development, differentiation, and metabolism. Zinc transporters (ZnTs) play a fundamental role in cellular zinc homeostasis. ZnTs are responsible of zinc efflux and are encoded by 10 genes belonging to solute carrier family 30A (SLC30A1-10), while zinc-regulated transporter (ZRT)/iron-regulated transporter (IRT)-like protein (ZIP) transporters are responsible for the influx of zinc into the cytoplasm and are encoded by 14 genes belonging to solute carrier family 39A (SLC39A1-14). In this study, we analyzed, by transcriptome analysis, the microRNA levels of ZnT-encoding and ZIP-encoding genes in colorectal cancer (CRC) samples matched to normal colon tissues and in CRC cell lines. Results revealed an upregulation of specific ZnT and ZIP transcripts in CRC. Upregulation of SLC30A5, SLC30A6, SLC30A7 transcripts, encoding zinc efflux transporters ZnT5, ZnT6, ZnT7, localized on endoplasmic reticulum membranes, might be part of a coordinated transcriptional program associated to the increased activity of the early secretory pathway, while transcriptional upregulation of several specific ZIP transporters (SLC39A6, SLC39A7, SLC39A9, SLC39A10, and SLC39A11) could contribute in meeting the increased demand of zinc in cancer cells. Moreover, exon-level analysis of SLC30A9, a nuclear receptor coactivator involved in the transcriptional regulation of Wnt-responsive genes, revealed the differential expression of alternative transcripts in CRC and normal colonic mucosa.

Nitric Oxide Disrupts Zinc Homeostasis in Salmonella enterica Serovar Typhimurium

Nitric oxide (NO·) produced by mammalian cells exerts antimicrobial actions that result primarily from the modification of protein thiols (S-nitrosylation) and metal centers. A comprehensive approach was used to identify novel targets of NO· in Salmonella enterica serovar Typhimurium (S. Typhimurium). Newly identified targets include zinc metalloproteins required for DNA replication and repair (DnaG, PriA, and TopA), protein synthesis (AlaS and RpmE), and various metabolic activities (ClpX, GloB, MetE, PepA, and QueC). The cytotoxic actions of free zinc are mitigated by the ZntA and ZitB zinc efflux transporters, which are required for S. Typhimurium resistance to zinc overload and nitrosative stress in vitro Zinc efflux also ameliorates NO·-dependent zinc mobilization following internalization by activated macrophages and is required for virulence in NO·-producing mice, demonstrating that host-derived NO· causes zinc stress in intracellular bacteria.IMPORTANCE Nitric oxide (NO·) is produced by macrophages in response to inflammatory stimuli and restricts the growth of intracellular bacteria. Mechanisms of NO·-dependent antimicrobial actions are incompletely understood. Here, we show that zinc metalloproteins are important targets of NO· in Salmonella, including the DNA replication proteins DnaG and PriA, which were hypothesized to be NO· targets in earlier studies. Like iron, zinc is a cofactor for several essential proteins but is toxic at elevated concentrations. This study demonstrates that NO· mobilizes free zinc in Salmonella and that specific efflux transporters ameliorate the cytotoxic effects of free zinc during infection.