Inhibitory effect of divalent metal cations on zinc uptake via mouse Zrt-/Irt-like protein 8 (ZIP8)

Decoding the Implications of Zinc in the Development and Therapy of Leukemia

Zinc plays a central role in the hematological development. Therapeutic interventions with zinc are shown to improve the health status of patients with malignancies by stimulating the immune system and reducing side effects. Despite the abnormal zinc homeostasis in leukemia, the role and mechanisms of zinc signaling in leukemia development remain poorly understood. Recently, some important breakthroughs are made in laboratory and clinical studies of zinc in leukemia, such as the role of zinc in regulating ferroptosis and the effects of zinc in immunotherapy. Zinc-based strategies are urgently needed to refine the current zinc intervention regimen for side-effect free therapy in chemotherapy-intolerant patients. This review provides a comprehensive overview of the role of zinc homeostasis in leukemia patients and focuses on the therapeutic potential of zinc signaling modulation in leukemia.

Upregulation of Intracellular Zinc Ion Level after Differentiation of the Neural Stem/Progenitor Cells In Vitro with the Changes in Gene Expression of Zinc Transporters

We measured the intracellular zinc ion concentration of murine fetal neural stem/progenitor cells (NSPCs) and that in the differentiated cells. The NSPCs cultured with 1.5 μM Zn2+ proliferated slightly faster than that in the zinc-deficient medium and the intracellular zinc concentration of the NSPCs and that of their differentiated cells (DCs) cultured with 1.5 μM Zn2+ was 1.34-fold and 2.00-fold higher than those in the zinc-deficient medium, respectively. The zinc transporter genes upregulated over the 3.5-fold change were Zip1, Zip4, Zip12, Zip13, ZnT1, ZnT8, and ZnT10 whereas the only downregulated one was Zip8 during the differentiation of NSPCs to DCs. The cell morphologies of both NSPCs and DCs in the low oxygen culture condition consisting of 2%O2 and 5%CO2, the high carbon dioxide condition consisting of 21%O2 and 10%CO2, and the normal condition consisting of 21%O2 and 5%CO2 were essentially the same each other. The expression of Zip4, Zip8, Zip12, and Zip14 was not drastically changed depending on the O2 and CO2 concentrations.

Evolution, classification, and mechanisms of transport, activity regulation, and substrate specificity of ZIP metal transporters

The Zrt/Irt-like protein (ZIP) family consists of ubiquitously expressed divalent d-block metal transporters that play central roles in the uptake, secretion, excretion, and distribution of several essential and toxic metals in living organisms. The past few years has witnessed rapid progress in the molecular basis of these membrane transport proteins. In this critical review, we summarize the research progress at the molecular level of the ZIP family and discuss the future prospects. Furthermore, an evolutionary path for the unique ZIP fold and a new classification of the ZIP family are proposed based on the presented structural and sequence analyses.

Protection of cultured vascular endothelial cells against cadmium cytotoxicity by simultaneous treatment or pretreatment with manganese

Cadmium is a heavy metal that pollutes the environment and foods and is a risk factor for vascular disorders. We have previously demonstrated that pretreatment of vascular endothelial cells with zinc and copper protects the cells against cadmium cytotoxicity. In contrast, cadmium cytotoxicity was potentiated in cells following exposure to lead, thereby indicating that in vascular endothelial cells, cadmium cytotoxicity can be differentially modified by the co-occurrence of other heavy metals. In this study, we revealed that simultaneous treatment or pretreatment with manganese protects vascular endothelial cells against cadmium cytotoxicity. Intracellular accumulation of cadmium was observed to be reduced by simultaneous treatment with manganese, although not by pretreatment. The mRNA expression of metal transporters that regulate the uptake of both cadmium and manganese (ZIP8, ZIP14, and DMT1) remained unaffected by either simultaneous treatment or pretreatment with manganese, and simultaneous treatment with manganese suppressed the cadmium-induced expression of metallothionein but pretreatment with manganese did not exhibit such suppressive effect. Thus, the protection of vascular endothelial cells against cadmium cytotoxicity conferred by simultaneous treatment with manganese is assumed to be partially attributed to a reduction in the intracellular accumulation of cadmium, whereas the effects of pretreatment with manganese are independent of both the reduced intracellular accumulation of cadmium and the induction of metallothionein. These observations accordingly indicate that the protective effects of manganese are mediated via alternative (as yet unidentified) mechanisms.

Multiple Targets of Toxicity in Environmental Exposure to Low-Dose Cadmium

Dietary assessment reports and population surveillance programs show that chronic exposure to low levels of environmental cadmium (Cd) is inevitable for most people, and adversely impacts the health of children and adults. Based on a risk assessment model that considers an increase in the excretion of β₂-microglobulin (β₂M) above 300 μg/g creatinine to be the "critical" toxicity endpoint, the tolerable intake level of Cd was set at 0.83 µg/kg body weight/day, and a urinary Cd excretion rate of 5.24 µg/g creatinine was considered to be the toxicity threshold level. The aim of this review is to draw attention to the many other toxicity endpoints that are both clinically relevant and more appropriate to derive Cd exposure limits than a β₂M endpoint. In the present review, we focus on a reduction in the glomerular filtration rate and diminished fecundity because chronic exposure to low-dose Cd, reflected by its excretion levels as low as 0.5 µg/g creatinine, have been associated with dose-dependent increases in risk of these pathological symptoms. Some protective effects of the nutritionally essential elements selenium and zinc are highlighted. Cd-induced mitochondrial dysfunction is discussed as a potential mechanism underlying gonadal toxicities and infertility.

Identification of a selective manganese ionophore that enables nonlethal quantification of cellular manganese

Available assays for measuring cellular manganese (Mn) levels require cell lysis, restricting longitudinal experiments and multiplexed outcome measures. Conducting a screen of small molecules known to alter cellular Mn levels, we report here that one of these chemicals induces rapid Mn efflux. We describe this activity and the development and implementation of an assay centered on this small molecule, named manganese-extracting small molecule (MESM). Using inductively-coupled plasma-MS, we validated that this assay, termed here "manganese-extracting small molecule estimation route" (MESMER), can accurately assess Mn in mammalian cells. Furthermore, we found evidence that MESM acts as a Mn-selective ionophore, and we observed that it has increased rates of Mn membrane transport, reduced cytotoxicity, and increased selectivity for Mn over calcium compared with two established Mn ionophores, calcimycin (A23187) and ionomycin. Finally, we applied MESMER to test whether prior Mn exposures subsequently affect cellular Mn levels. We found that cells receiving continuous, elevated extracellular Mn accumulate less Mn than cells receiving equally-elevated Mn for the first time for 24 h, indicating a compensatory cellular homeostatic response. Use of the MESMER assay versus a comparable detergent lysis-based assay, cellular Fura-2 Mn extraction assay, reduced the number of cells and materials required for performing a similar but cell lethality-based experiment to 25% of the normally required sample size. We conclude that MESMER can accurately quantify cellular Mn levels in two independent cells lines through an ionophore-based mechanism, maintaining cell viability and enabling longitudinal assessment within the same cultures.

Zinc supplementation alleviates OTA-induced oxidative stress and apoptosis in MDCK cells by up-regulating metallothioneins

AIMS

The present study was to investigate the protective effects of Zn supplementation in OTA-induced apoptosis of Madin-Darby canine kidney (MDCK) epithelial cells and explore the potential mechanisms. Aiming to provides a new insight into the treatment strategy of OTA-induced nephrotoxicity by nutritional regulation.

MAIN METHODS

Initially, through MTT and LDH assay revealed that Zn supplementation significantly suppressed OTA-induced cytotoxicity in MDCK cells. Then, the production of reactive oxygen species (ROS) was detected by using a DCFH-DA assay. Annexin V-FITC/PI, Hoechst 33258 staining and Flow cytometry were used to detect the apoptosis. The expressions of apoptosis-related molecules were determined by RT-PCR, Western blotting. Interestingly, OTA treatment slightly increased the levels of Metallothionein-1 (MT-1) and Metallothionein-2 (MT-2) by using RT-PCR, Western blotting assay; while Zn supplementation further improved the increase of MT-1 and MT-2 induced by OTA. However, the inhibitive effects of Zn supplementation were significantly blocked after double knockdown of MT-1 and MT-2 by using Small Interfering RNA (siRNA) Transfection method.

KEY FINDINGS

Our study provides supportive data for the potential roles of Zn in reducing OTA-induced oxidative stress and apoptosis in MDCK cells.

SIGNIFICANCE

Zn is one of the key structural components of many proteins, which plays an important role in several physiological processes such as cell survival and apoptosis. This metal is expected to contribute to the conservative and adjuvant treatment of kidney disease and should therefore be investigated further.

Induction of the metal transporter ZIP8 by interferon gamma in intestinal epithelial cells: Potential role of metal dyshomeostasis in Crohn's disease

Transition metals are required for intestinal homeostasis and provide essential nutrients for the resident microbiota. Abnormalities in metal homeostasis are common in Crohn's disease (CD), but remain poorly defined and causes appear multifactorial. There has been renewed interest in understanding these mechanisms with the discovery of an association between a coding variant in SLC39A8 (rs13107325; ZIP8 A391T) and increased CD risk. SLC39A8 encodes the protein ZIP8, a metal transporter that is induced under inflammatory stimuli; however, studies of its gut-specific functions are lacking. Here, we show that SLC39A8 mRNA is differentially expressed in active CD with a high positive correlation with markers of disease severity, including CXCL8, TNFα, IFNγ, and calprotectin. SLC39A8 expression exhibits a negative correlation with SLC39A4 and SLC39A5, two key zinc importers in absorptive enterocytes, and a lack of correlation with two manganese transporters, SLC39A14 and SLC11A2. Immunohistochemistry demonstrates ZIP8 expression in intestinal epithelial cells and immune cells of the lamina propria. Patients with CD exhibit variable patterns of ZIP8 subcellular localization within IECs. In ileal enteroids, SLC39A8 was induced by IFNγ and IFNγ + TNFα, but not by TNFα alone, independent of NF-κB activation. IFNγ also down-regulated SLC39A5. To explore the functional implications of disease-associated genetic variation, in over-expression experiments in HEK293A cells, ZIP8 A391T was associated with increased TNFα-induced NF-κB activation, consistent with a loss of negative regulation. Taken together, these results suggest a potential role for ZIP8 in intestinal inflammation, induced by IFNγ in the intestinal epithelial compartment, and that perturbations in negative regulation of NF-κB by ZIP8 A391T may contribute to CD pathogenesis.

Role of ZIP8 in regulation of cisplatin sensitivity through Bcl-2

ZIP8 is a membrane transporter that facilitates the uptake of divalent metals (e.g., Zn, Mn, Fe, Cd) and the mineral selenite in anionic form. ZIP8 functionality has been recently reported to regulate cell proliferation, migration and cytoskeleton arrangement, exhibiting an essential role for normal physiology. In this study, we report a ZIP8 role in chemotherapy response. We show ZIP8 regulates cell sensitivity to the anti-cancer drug cisplatin. Overexpression of ZIP8 in mouse embryonic fibroblast (MEF) cells induces cisplatin sensitivity, while knockout of ZIP8 in leukemia HAP1 cells leads to cisplatin resistance. In ZIP8 altered cells and transgenic mice, we show cisplatin is not a direct ZIP8 substrate. Further studies demonstrate that ZIP8 regulates anti-apoptotic protein Bcl-2. ZIP8 overexpression decreases Bcl-2 levels in cultured cells, mice lung and liver tissue while loss of ZIP8 elevates Bcl-2 expression in HAP1 cells and liver tissue. We also observe that ZIP8 overexpression modulates cisplatin-induced cell apoptosis, manifested by the increased protein level of cleaved Caspase-3. Since Bcl-2 elevation was previously discovered to induce cisplatin drug resistance, our results suggest ZIP8 may modulate cisplatin drug responses as well as apoptosis through Bcl-2. We therefore conclude ZIP8 is a new molecule to be involved in cisplatin drug responses and is predicted as a genetic factor to be considered in cisplatin therapy.

Elemental Ingredients in the Macrophage Cocktail: Role of ZIP8 in Host Response to Mycobacterium tuberculosis

Tuberculosis (TB) is a global epidemic caused by the infection of human macrophages with the world's most deadly single bacterial pathogen, Mycobacterium tuberculosis (M.tb). M.tb resides in a phagosomal niche within macrophages, where trace element concentrations impact the immune response, bacterial metal metabolism, and bacterial survival. The manipulation of micronutrients is a critical mechanism of host defense against infection. In particular, the human zinc transporter Zrt-/Irt-like protein 8 (ZIP8), one of 14 ZIP family members, is important in the flux of divalent cations, including zinc, into the cytoplasm of macrophages. It also has been observed to exist on the membrane of cellular organelles, where it can serve as an efflux pump that transports zinc into the cytosol. ZIP8 is highly inducible in response to M.tb infection of macrophages, and we have observed its localization to the M.tb phagosome. The expression, localization, and function of ZIP8 and other divalent cation transporters within macrophages have important implications for TB prevention and dissemination and warrant further study. In particular, given the importance of zinc as an essential nutrient required for humans and M.tb, it is not yet clear whether ZIP-guided zinc transport serves as a host protective factor or, rather, is targeted by M.tb to enable its phagosomal survival.