ZIP4 upregulation aggravates nucleus pulposus cell degradation by promoting inflammation and oxidative stress by mediating the HDAC4-FoxO3a axis

BACKGROUND

Extracellular matrix metabolism dysregulation in nucleus pulposus (NP) cells represents a crucial pathophysiological feature of intervertebral disc degeneration (IDD). Our study elucidates the role and mechanism of Testis expressed 11 (TEX11, also called ZIP4) extracellular matrix degradation in the NP.

MATERIALS AND METHODS

Interleukin-1β (IL-1β) and H2O2 were used to treat NP cells to establish an IDD cell model. Normal NP tissues and NP tissues from IDD patients were harvested. ZIP4 mRNA and protein profiles in NP cells and tissues were examined. Enzyme-linked immunosorbent assay (ELISA) confirmed the profiles of TNF-α, IL-6, MDA, and SOD in NP cells. The alterations of reactive oxygen species (ROS), lactate dehydrogenase (LDH), COX2, iNOS, MMP-3, MMP-13, collagen II, aggrecan, FoxO3a, histone deacetylase 4 (HDAC4), Sirt1 and NF-κB levels in NP cells were determined using different assays.

RESULTS

The ZIP4 profile increased in the NP tissues of IDD patients and IL-1β- or H2O2-treated NP cells. ZIP4 upregulation bolstered inflammation and oxidative stress in NP cells undergoing IL-1β treatment and exacerbated their extracellular matrix degradation, whereas ZIP4 knockdown produced the opposite outcome. Mechanistically, ZIP4 upregulated HDAC4 and enhanced NF-κB phosphorylation while repressing Sirt1 and FoxO3a phosphorylation levels. HDAC4 knockdown or Sirt1 promotion attenuated the effects mediated by ZIP4 overexpression in NP cells.

CONCLUSIONS

ZIP4 upregulation aggravates the extracellular matrix (ECM) degradation of NP cells by mediating inflammation and oxidative stress through the HDAC4-FoxO3a axis.

Cell-based transport assay to study kinetics and substrate specificity of human ZIPs

Kinetic study of human ZIPs is crucial for understanding the transport mechanism and the molecular basis of substrate specificity. In this chapter, we describe the detailed experimental procedures for functional studies of two human ZIPs, including the zinc-preferring ZIP4 and the multi-metal transporter ZIP8, by using the cell-based transport assays. Kinetic study of ZIP4 is elaborated in the first section; in the second section, comparison of ZIP4 and ZIP8 in terms of the zinc/cadmium selectivity is performed by using an internal competition assay adapted from the established cell-based approach. The protocols provided in this chapter will facilitate mechanistic and engineering studies of the ZIPs.

ZIP4 is required for normal progression of synapsis and for over 95% of crossovers in wheat meiosis

Tetraploid (AABB) and hexaploid (AABBDD) wheat have multiple sets of similar chromosomes, with successful meiosis and preservation of fertility relying on synapsis and crossover (CO) formation only taking place between homologous chromosomes. In hexaploid wheat, the major meiotic gene TaZIP4-B2 (Ph1) on chromosome 5B, promotes CO formation between homologous chromosomes, whilst suppressing COs between homeologous (related) chromosomes. In other species, ZIP4 mutations eliminate approximately 85% of COs, consistent with loss of the class I CO pathway. Tetraploid wheat has three ZIP4 copies: TtZIP4-A1 on chromosome 3A, TtZIP4-B1 on 3B and TtZIP4-B2 on 5B. Here, we have developed single, double and triple zip4 TILLING mutants and a CRISPR Ttzip4-B2 mutant, to determine the effect of ZIP4 genes on synapsis and CO formation in the tetraploid wheat cultivar 'Kronos'. We show that disruption of two ZIP4 gene copies in Ttzip4-A1B1 double mutants, results in a 76-78% reduction in COs when compared to wild-type plants. Moreover, when all three copies are disrupted in Ttzip4-A1B1B2 triple mutants, COs are reduced by over 95%, suggesting that the TtZIP4-B2 copy may also affect class II COs. If this is the case, the class I and class II CO pathways may be interlinked in wheat. When ZIP4 duplicated and diverged from chromosome 3B on wheat polyploidization, the new 5B copy, TaZIP4-B2, could have acquired an additional function to stabilize both CO pathways. In tetraploid plants deficient in all three ZIP4 copies, synapsis is delayed and does not complete, consistent with our previous studies in hexaploid wheat, when a similar delay in synapsis was observed in a 59.3 Mb deletion mutant, ph1b, encompassing the TaZIP4-B2 gene on chromosome 5B. These findings confirm the requirement of ZIP4-B2 for efficient synapsis, and suggest that TtZIP4 genes have a stronger effect on synapsis than previously described in Arabidopsis and rice. Thus, ZIP4-B2 in wheat accounts for the two major phenotypes reported for Ph1, promotion of homologous synapsis and suppression of homeologous COs.

Investigation of ZIP4, ZO-1, and CLAUDIN-1 expression in thyroid tumours by immunohistochemistry and real-time polymerase chain reaction methods

Thyroid neoplasms are the most common endocrine malignancies. ZIP4 is an intramembranous zinc trans membrane protein. Zinc plays a central role in the activation of transcription factors, and zinc transporters. This affects tumour migration, invasion, and cell proliferation. ZO-1 and Claudin-1 are important tight junction proteins whose amounts increase and decrease in various cancers. In this study, we aimed to investigate the expression of ZIP4, ZO-1, and Claudin-1 in thyroid tumours and the relationship of this expression with tumour types and prognostic parameters. ZIP4, ZO-1, and Claudin-1 were studied in all cases by immunohistochemical and Real-Time PCR methods. ZIP4 and Claudin-1 tended to be expressed more in cases with tumours, while ZO-1 in cases with and without tumours. Expression of ZIP4 and Claudin-1 by real-time polymerase chain reaction showed a significant difference between histological subtypes, and this difference was not observed with ZO-1. It was observed that the presence of metastasis increased with the expression of ZIP4 and Claudin-1, and there was no significant change with ZO-1. We think that Claudin-1 and ZIP4 expression can be used as an important marker in terms of showing poor prognosis and susceptibility to metastasis in thyroid tumours, and in developing targeted therapy.

Dietary zinc restriction affects the expression of genes related to immunity and stress response in the small intestine of pigs

Zinc (Zn) is an essential mineral and its deficiency manifests in non-specific clinical signs that require long time to develop. The response of swine intestine to Zn restriction was evaluated to identify early changes that can be indicative of Zn deficiency. Twenty-seven pigs (body weight = 77⋅5 ± 2⋅5 kg) were assigned to one of three diets: diet without added Zn (Zn-restricted diet, ZnR), and ZnR-supplemented with either 50 (Zn50) or 100 mg of Zn/kg of diet (Zn100) of Zn supplied by ZnCl₂. After 32 d consuming the diets, serum Zn concentration in ZnR pigs was below the range of 0⋅59-1⋅37 μg/ml considered sufficient, thereby confirming subclinical Zn deficiency. Pigs showed no obvious health or growth changes. RNA-seq analysis followed by qPCR showed decreased expression of metallothionein-1 (MT1) (P < 0⋅05) and increased expression of Zn transporter ZIP4 (P < 0⋅05) in jejunum and ileum of ZnR pigs compared with Zn-supplemented pigs. Ingenuity pathway analysis revealed that Zn50 and Zn100 induced changes in genes related to nucleotide excision repair and integrin signalling pathways. The top gene network in the ZnR group compared with Zn100 was related to lipid and drug metabolism; and compared with Zn50, was related to cellular proliferation, assembly and organisation. Dietary Zn concentrations resulted in differences in genes related to immune pathways. Our analysis showed that small intestine presents changes associated with Zn deficiency after 32 d of Zn restriction, suggesting that the intestine could be a sentinel organ for Zn deficiency.

RASSF1A independence and early galectin-1 upregulation in PIK3CA-induced hepatocarcinogenesis: new therapeutic venues

Aberrant activation of the phosphoinositide 3‐kinase (PI3K)/AKT/mTOR and Ras/mitogen‐activated protein kinase (MAPK) pathways is a hallmark of hepatocarcinogenesis. In a subset of hepatocellular carcinomas (HCCs), PI3K/AKT/mTOR signaling dysregulation depends on phosphatidylinositol‐4,5‐bisphosphate 3‐kinase, catalytic subunit alpha (PIK3CA) mutations, while RAS/MAPK activation is partly attributed to promoter methylation of the tumor suppressor Ras association domain‐containing protein 1 (RASSF1A). To evaluate a possible cocarcinogenic effect of PIK3CA activation and RASSF1A knockout, plasmids expressing oncogenic forms of PIK3CA (E545K or H1047R mutants) were delivered to the liver of RASSF1A knockout and wild‐type mice by hydrodynamic tail vein injection combined with sleeping beauty‐mediated somatic integration. Transfection of either PIK3CA E545K or H1047R mutants sufficed to induce HCCs in mice irrespective of RASSF1A mutational background. The related tumors displayed a lipogenic phenotype with upregulation of fatty acid synthase and stearoyl‐CoA desaturase‐1 (SCD1). Galectin‐1, which was commonly upregulated in preneoplastic lesions and tumors, emerged as a regulator of SCD1. Co‐inhibitory treatment with PIK3CA inhibitors and the galectin‐1 inhibitor OTX008 resulted in synergistic cytotoxicity in human HCC cell lines, suggesting novel therapeutic venues.

ZIP4 promotes non-small cell lung cancer metastasis by activating snail-N-cadherin signaling axis

Non-small cell lung cancer (NSCLC) is one of the most critical health problems worldwide, with high incidence and poor survival rate. A zinc importer ZIP4 has been implicated in the process of tumor growth and metastasis of many cancers. However, its exact role and the underlying mechanism in NSCLC remains to be elucidated. In the present study, we found that human ZIP4 was substantially overexpressed in NSCLC tissues and was correlated with poor overall survival (OS) and progression-free survival (PFS). Overexpression of ZIP4 promoted cell migration, invasion and metastasis both in vitro and in a mouse lung metastasis model. Silencing of ZIP4 attenuated migration, invasion and metastasis. Mechanistically, overexpression of ZIP4 increased the expression of Snail, Slug and N-cadherin while genetic inactivation of ZIP4 downregulated the expression of above-mentioned genes. Further analysis showed that transcriptional factor Snail which modulates N-cadherin was involved in the process of ZIP4-mediated NSCLC migration and invasion. We also demonstrated that ZIP4 positively correlates with the levels of Snail, Slug and N-cadherin in mice lung metastasis tumors. Together, these results suggest that ZIP4 acts as an important regulator of Snail-N-cadherin signaling axis in promoting NSCLC progression and may serve as a novel predictive marker and therapeutic target in NSCLC.

A Novel ZIP4-HDAC4-VEGFA Axis in High-Grade Serous Ovarian Cancer

Simple Summary

Despite tremendous research efforts, epithelial ovarian cancer (EOC) remains one of the most difficult cancers to detect early and treat successfully for >5-year survival. We have recently shown that ZIP4, a zinc transporter, is a novel cancer stem cell (CSC) marker and a therapeutic target for EOC. The current work focuses on developing new strategies to target ZIP4 and inhibit its CSC activities in EOC. We found that cells expressing high levels of ZIP4 were supersensitive to a group of inhibitors called HDACis. One of the major targets of these inhibitors is a protein called HDAC4. We revealed the new molecular bases for the ZIP4-HDAC4 axis and tested the efficacies of targeting this axis in the lab and in mouse models. Our study provides a new mechanistic-based targeting strategy for EOC.

Abstract

We have recently identified ZIP4 as a novel cancer stem cell (CSC) marker in high-grade serous ovarian cancer (HGSOC). While it converts drug-resistance to cisplatin (CDDP), we unexpectedly found that ZIP4 induced sensitization of HGSOC cells to histone deacetylase inhibitors (HDACis). Mechanistically, ZIP4 selectively upregulated HDAC IIa HDACs, with little or no effect on HDACs in other classes. HDAC4 knockdown (KD) and LMK-235 inhibited spheroid formation in vitro and tumorigenesis in vivo, with hypoxia inducible factor-1 alpha (HIF1α) and endothelial growth factor A (VEGFA) as functional downstream mediators of HDAC4. Moreover, we found that ZIP4, HDAC4, and HIF1α were involved in regulating secreted VEGFA in HGSOC cells. Furthermore, we tested our hypothesis that co-targeting CSC via the ZIP4-HDAC4 axis and non-CSC using CDDP is necessary and highly effective by comparing the effects of ZIP4-knockout/KD, HDAC4-KD, and HDACis, in the presence or absence of CDDP on tumorigenesis in mouse models. Our results showed that the co-targeting strategy was highly effective. Finally, data from human HGSOC tissues showed that ZIP4 and HDAC4 were upregulated in a subset of recurrent tumors, justifying the clinical relevance of the study. In summary, our study provides a new mechanistic-based targeting strategy for HGSOC.

Molecular Basis of Zinc-Dependent Endocytosis of Human ZIP4 Transceptor

Nutrient transporters can be rapidly removed from the cell surface via substrate-stimulated endocytosis as a way to control nutrient influx, but the molecular underpinnings are not well understood. In this work, we focus on zinc-dependent endocytosis of human ZIP4 (hZIP4), a zinc transporter that is essential for dietary zinc uptake. Structure-guided mutagenesis and internalization assay reveal that hZIP4 per se acts as the exclusive zinc sensor, with the transport site’s being responsible for zinc sensing. In an effort of seeking sorting signal, a scan of the longest cytosolic loop (L2) leads to identification of a conserved Leu-Gln-Leu motif that is essential for endocytosis. Partial proteolysis of purified hZIP4 demonstrates a structural coupling between the transport site and the L2 upon zinc binding, which supports a working model of how zinc ions at physiological concentration trigger a conformation-dependent endocytosis of the zinc transporter. This work provides a paradigm on post-translational regulation of nutrient transporters.

Cell surface expression of ZIP4, a transporter for intestinal zinc uptake, is regulated by zinc availability. Zhang et al. report that human ZIP4 acts as the exclusive zinc sensor in initiating the zinc-dependent endocytosis, and a cytosolic motif is essential for sorting signal formation, indicating that ZIP4 is a transceptor.

A Duplicated Copy of the Meiotic Gene ZIP4 Preserves up to 50% Pollen Viability and Grain Number in Polyploid Wheat

Simple Summary

On wheat polyploidisation, the major meiotic gene ZIP4, duplicated and diverged, such that tetraploid and hexaploid wheat each carry three and four copies of ZIP4, respectively. Surprisingly, this study demonstrates that, in hexaploid wheat, despite the presence of the other three ZIP4 copies, the duplicated ZIP4 copy is required to prevent major abnormalities during meiosis. Although there is greater disruption of subsequent male rather than female fertility, the duplicated ZIP4 copy preserves up to 50% of the grain number. High wheat fertility is important since it is consumed by over 4.5 billion people on the planet, of whom 2.5 billion are dependent on it. This study highlights the potentially extraordinary value of the wheat ZIP4 duplication, mandating further studies to unravel the complexity of the ZIP4 phenotype in this global crop.

Abstract

Although most flowering plants are polyploid, little is known of how the meiotic process evolves after polyploidisation to stabilise and preserve fertility. On wheat polyploidisation, the major meiotic gene ZIP4 on chromosome 3B duplicated onto 5B and diverged (TaZIP4-B2). TaZIP4-B2 was recently shown to promote homologous pairing, synapsis and crossover, and suppress homoeologous crossover. We therefore suspected that these meiotic stabilising effects could be important for preserving wheat fertility. A CRISPR Tazip4-B2 mutant was exploited to assess the contribution of the 5B duplicated ZIP4 copy in maintaining pollen viability and grain setting. Analysis demonstrated abnormalities in 56% of meiocytes in the Tazip4-B2 mutant, with micronuclei in 50% of tetrads, reduced size in 48% of pollen grains and a near 50% reduction in grain number. Further studies showed that most of the reduced grain number occurred when Tazip4-B2 mutant plants were pollinated with the less viable Tazip4-B2 mutant pollen rather than with wild type pollen, suggesting that the stabilising effect of TaZIP4-B2 on meiosis has a greater consequence in subsequent male, rather than female gametogenesis. These studies reveal the extraordinary value of the wheat chromosome 5B TaZIP4-B2 duplication to agriculture and human nutrition. Future studies should further investigate the role of TaZIP4-B2 on female fertility and assess whether different TaZIP4-B2 alleles exhibit variable effects on meiotic stabilisation and/or resistance to temperature change.

Effect of pinealectomy and melatonin supplementation on metallothionein, ZnT2, ZIP2, ZIP4 and zinc levels in rat small intestine

We investigated the relations among levels of metallothionein (MT); zinc (Zn) transport proteins, ZnT2, ZIP2 (ZRT and IRT-like proteins); and ZIP4, which enable Zn absorption in the small intestine of rats. We also investigated tissue Zn levels in the small intestine. We used four groups of adult male rats: group 1, control; group 2, pinealectomy (Px); group 3, Px + melatonin (MEL); group 4, MEL only. Animals in groups 3 and 4 were administered 5 mg/kg/day MEL for four weeks. At the end of the study, all animals were sacrificed and samples of duodenum, jejunum and ileum were harvested to analyze ZnT2, ZIP2, ZIP4 and MT levels using immunohistochemistry, and tissue Zn levels were measured by atomic absorption spectrophotometry. The lowest ZnT2 levels in the duodenum, jejunum and ileum, and the lowest ZIP2 levels in the duodenum and ileum were found in group 2. The lowest ZIP4 levels were found in the duodenum and jejunum, and the lowest MT levels in the duodenum and ileum were found in group 2. The highest MT values in the ileum were found in group 4. We found that ZnT2, ZIP2, ZIP4 and MT levels were reduced in the ileum compared to controls following Px, but levels approached control values after MEL administration. By its effects on ZnT2, ZIP2, ZIP4 and MT levels, MEL participates in the absorption of Zn in the rat small intestine.

Zinc transporter mutations linked to acrodermatitis enteropathica disrupt function and cause mistrafficking

ZIP4 is a representative member of the Zrt-/Irt-like protein (ZIP) transporter family and responsible for zinc uptake from diet. Loss-of-function mutations of human ZIP4 (hZIP4) drastically reduce zinc absorption, causing a life-threatening autosomal recessive disorder, acrodermatitis enteropathica (AE). These mutations occur not only in the conserved transmembrane zinc transport machinery, but also in the extracellular domain (ECD) of hZIP4, which is only present in a fraction of mammalian ZIPs. How these AE-causing ECD mutations lead to ZIP4 malfunction has not be fully clarified. In this work, we characterized all seven confirmed AE-causing missense mutations in hZIP4-ECD and found that the variants exhibited completely abolished zinc transport activity in a cell-based transport assay. Although the variants were able to be expressed in HEK293T cells, they failed to traffic to the cell surface and were largely retained in the ER with immature glycosylation. When the corresponding mutations were introduced in the ECD of ZIP4 from Pteropus Alecto, a close homolog of hZIP4, the variants exhibited structural defects or reduced thermal stability, which likely accounts for intracellular mistrafficking of the AE-associated variants and as such a total loss of zinc uptake activity. This work provides a molecular pathogenic mechanism for AE.

Manganese Accumulation in the Brain via Various Transporters and Its Neurotoxicity Mechanisms

Manganese (Mn) is an essential trace element, serving as a cofactor for several key enzymes, such as glutamine synthetase, arginase, pyruvate decarboxylase, and mitochondrial superoxide dismutase. However, its chronic overexposure can result in a neurological disorder referred to as manganism, presenting symptoms similar to those inherent to Parkinson’s disease. The pathological symptoms of Mn-induced toxicity are well-known, but the underlying mechanisms of Mn transport to the brain and cellular toxicity leading to Mn’s neurotoxicity are not completely understood. Mn’s levels in the brain are regulated by multiple transporters responsible for its uptake and efflux, and thus, dysregulation of these transporters may result in Mn accumulation in the brain, causing neurotoxicity. Its distribution and subcellular localization in the brain and associated subcellular toxicity mechanisms have also been extensively studied. This review highlights the presently known Mn transporters and their roles in Mn-induced neurotoxicity, as well as subsequent molecular and cellular dysregulation upon its intracellular uptakes, such as oxidative stress, neuroinflammation, disruption of neurotransmission, α-synuclein aggregation, and amyloidogenesis.

ZIP4 Is a Novel Cancer Stem Cell Marker in High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) is one of the most deadly and heterogenic cancers. We have recently shown that ZIP4 (gene name SLC39A4), a zinc transporter, is functionally involved in cancer stem cell (CSC)-related cellular activities in HGSOC. Here, we identified ZIP4 as a novel CSC marker in HGSOC. Fluorescence-activated cell sorter (FACS)-sorted ZIP4⁺, but not ZIP4^- cells, formed spheroids and displayed self-renewing and differentiation abilities. Over-expression of ZIP4 conferred drug resistance properties in vitro. ZIP4⁺, but not ZIP4^- cells, formed tumors/ascites in vivo. We conducted limiting dilution experiments and showed that 100-200 ZIP4⁺ cells from both PE04 and PEA2 cells formed larger tumors than those from 100-200 ALDH⁺ cells in mice. Mechanistically, we found that ZIP4 was an upstream regulator of another CSC-marker, NOTCH3, in HGSOC cells. NOTCH3 was functionally involved in spheroid formation in vitro and tumorigenesis in vivo in HGSOC. Genetic compensation studies showed that NOTCH3, but not NOTCH1, was a critical downstream mediator of ZIP4. Furthermore, NOTCH3, but not NOTCH1, physically bound to ZIP4. Collectively, our data suggest that ZIP4 is a novel CSC marker and the new ZIP4-NOTCH3 axis represents important therapeutic targets in HGSOC.

Iron and Zinc Homeostasis and Interactions: Does Enteric Zinc Excretion Cross-Talk with Intestinal Iron Absorption?

Iron and zinc are essential micronutrients required for growth and health. Deficiencies of these nutrients are highly prevalent among populations, but can be alleviated by supplementation and food fortification. Cross-sectional studies in humans showed positive association of serum zinc levels with hemoglobin and markers of iron status. Dietary restriction of zinc or intestinal specific conditional knock out of ZIP4 (SLC39A4), an intestinal zinc transporter, in experimental animals demonstrated iron deficiency anemia and tissue iron accumulation. Similarly, increased iron accumulation has been observed in cultured cells exposed to zinc deficient media. These results together suggest a potential role of zinc in modulating intestinal iron absorption and mobilization from tissues. Studies in intestinal cell culture models demonstrate that zinc induces iron uptake and transcellular transport via induction of divalent metal iron transporter-1 (DMT1) and ferroportin (FPN1) expression, respectively. It is interesting to note that intestinal cells are exposed to very high levels of zinc through pancreatic secretions, which is a major route of zinc excretion from the body. Therefore, zinc appears to be modulating the iron metabolism possibly via regulating the DMT1 and FPN1 levels. Herein we critically reviewed the available evidence to hypothesize novel mechanism of Zinc-DMT1/FPN1 axis in regulating intestinal iron absorption and tissue iron accumulation to facilitate future research aimed at understanding the yet elusive mechanisms of iron and zinc interactions.

The histidine-rich loop in the extracellular domain of ZIP4 binds zinc and plays a role in zinc transport

The Zrt-/Irt-like protein (ZIP) family mediates zinc influx from extracellular space or intracellular vesicles/organelles, playing a central role in systemic and cellular zinc homeostasis. Out of the 14 family members encoded in human genome, ZIP4 is exclusively responsible for zinc uptake from dietary food and dysfunctional mutations of ZIP4 cause a life-threatening genetic disorder, Acrodermatitis Enteropathica (AE). About half of the missense AE-causing mutations occur within the large N-terminal extracellular domain (ECD), and our previous study has shown that ZIP4-ECD is crucial for optimal zinc uptake but the underlying mechanism has not been clarified. In this work, we examined zinc binding to the isolated ZIP4-ECD from Pteropus Alecto (black fruit bat) and located zinc-binding sites with a low micromolar affinity within a histidine-rich loop ubiquitously present in ZIP4 proteins. Zinc binding to this protease-susceptible loop induces a small and highly localized structural perturbation. Mutagenesis and functional study on human ZIP4 by using an improved cell-based zinc uptake assay indicated that the histidine residues within this loop are not involved in preselection of metal substrate but play a role in promoting zinc transport. The possible function of the histidine-rich loop as a metal chaperone facilitating zinc binding to the transport site and/or a zinc sensor allosterically regulating the transport machinery was discussed. This work helps to establish the structure/function relationship of ZIP4 and also sheds light on other metal transporters and metalloproteins with clustered histidine residues.

An extracellular histidine-containing motif in the zinc transporter ZIP4 plays a role in zinc sensing and zinc-induced endocytosis in mammalian cells

Zinc is an essential trace element that serves as a cofactor for enzymes in critical biochemical processes and also plays a structural role in numerous proteins. Zinc transporter ZIP4 (ZIP4) is a zinc importer required for dietary zinc uptake in the intestine and other cell types. Studies in cultured cells have reported that zinc stimulates the endocytosis of plasma membrane-localized ZIP4 protein, resulting in reduced cellular zinc uptake. Thus, zinc-regulated trafficking of ZIP4 is a key means for regulating cellular zinc homeostasis, but the underlying mechanisms are not well understood. In this study, we used mutational analysis, immunoblotting, HEK293 cells, and immunofluorescence microscopy to identify a histidine-containing motif (³⁹⁸HTH) in the first extracellular loop that is required for high sensitivity to low zinc concentrations in a zinc-induced endocytic response of mouse ZIP4 (mZIP4). Moreover, using synthetic peptides with selective substitutions and truncated mZIP4 variants, we provide evidence that histidine residues in this motif coordinate a zinc ion in mZIP4 homodimers at the plasma membrane. These findings suggest that ³⁹⁸HTH is an important zinc-sensing motif for eliciting high-affinity zinc-stimulated endocytosis of mZIP4 and provide insight into cellular mechanisms for regulating cellular zinc homeostasis in mammalian cells.

Genome-Wide Transcription During Early Wheat Meiosis Is Independent of Synapsis, Ploidy Level, and the Ph1 Locus

Polyploidization is a fundamental process in plant evolution. One of the biggest challenges faced by a new polyploid is meiosis, particularly discriminating between multiple related chromosomes so that only homologous chromosomes synapse and recombine to ensure regular chromosome segregation and balanced gametes. Despite its large genome size, high DNA repetitive content and similarity between homoeologous chromosomes, hexaploid wheat completes meiosis in a shorter period than diploid species with a much smaller genome. Therefore, during wheat meiosis, mechanisms additional to the classical model based on DNA sequence homology, must facilitate more efficient homologous recognition. One such mechanism could involve exploitation of differences in chromosome structure between homologs and homoeologs at the onset of meiosis. In turn, these chromatin changes, can be expected to be linked to transcriptional gene activity. In this study, we present an extensive analysis of a large RNA-seq data derived from six different genotypes: wheat, wheat-rye hybrids and newly synthesized octoploid triticale, both in the presence and absence of the Ph1 locus. Plant material was collected at early prophase, at the transition leptotene-zygotene, when the telomere bouquet is forming and synapsis between homologs is beginning. The six genotypes exhibit different levels of synapsis and chromatin structure at this stage; therefore, recombination and consequently segregation, are also different. Unexpectedly, our study reveals that neither synapsis, whole genome duplication nor the absence of the Ph1 locus are associated with major changes in gene expression levels during early meiotic prophase. Overall wheat transcription at this meiotic stage is therefore highly resilient to such alterations, even in the presence of major chromatin structural changes. Further studies in wheat and other polyploid species will be required to reveal whether these observations are specific to wheat meiosis.

Zinc transporters are differentially expressed in human non-small cell lung cancer

Lung cancer is one of the most common human malignancies worldwide, but its oncogenesis process remains unclear. Recent studies demonstrated that zinc (Zn) and Zn transporters were associated with the development and progression of human cancers. The role of Zn transporters including ZIPs and ZnTs in lung cancer, however, has never been evaluated. Thus, we aimed to investigate the expression levels of all human Zn transporters, including 14 ZIPs and 10 ZnTs, in eight different lung cancer cell lines and paired human tumor tissues. We observed great variations in ZIPs and ZnTs mRNA levels across cell lines and human lung cancer specimens. ZIPs showed a tendency to be upregulated, while ZnTs exhibited a downward expression trend. ZIP4 was overexpressed in six lung cancer cell lines and 59% (26/44) of tumor tissues, which was consistent with results from lung cancer datasets including TCGA database. Our results indicated that the dysregulation of Zn transporters may contribute to lung tumorigenesis.

Introgression of the Aegilops speltoides Su1-Ph1 Suppressor into Wheat

Meiotic pairing between homoeologous chromosomes in polyploid wheat is inhibited by the Ph1 locus on the long arm of chromosome 5 in the B genome. Aegilops speltoides (genomes SS), the closest relative of the progenitor of the wheat B genome, is polymorphic for genetic suppression of Ph1. Using this polymorphism, two major suppressor loci, Su1-Ph1 and Su2-Ph1, have been mapped in Ae. speltoides. Su1-Ph1 is located in the distal, high-recombination region of the long arm of the Ae. speltoides chromosome 3S. Its location and tight linkage to marker Xpsr1205-3S makes Su1-Ph1 a suitable target for introgression into wheat. Here, Xpsr1205-3S was introgressed into hexaploid bread wheat cv. Chinese Spring (CS) and from there into tetraploid durum wheat cv. Langdon (LDN). Sequential fluorescence in situ hybridization and genomic in situ hybridization showed that an Ae. speltoides segment with Xpsr1205-3S replaced the distal end of the long arm of chromosome 3A. In the CS genetic background, the chromosome induced homoeologous chromosome pairing in interspecific hybrids with Ae. peregrina but not in progenies from crosses involving alien disomic substitution lines. In the LDN genetic background, the chromosome induced homoeologous chromosome pairing in both interspecific hybrids and progenies from crosses involving alien disomic substitution lines. We conclude that the recombined chromosome harbors Su1-Ph1 but its expression requires expression of complementary gene that is present in LDN but absent in CS. We suggest that it is unlikely that Su1-Ph1 and ZIP4-1, a paralog of Ph1 located on wheat chromosomes 3A and 3B and Ae. tauschii chromosome 3D, are equivalent. The utility of Su1-Ph1 for induction of recombination between homoeologous chromosomes in wheat is illustrated.

The novel ZIP4 regulation and its role in ovarian cancer

Our RNAseq analyses revealed that ZIP4 is a top gene up-regulated in more aggressive ovarian cancer cells. ZIP4's role in cancer stem cells has not been reported in any type of cancer. In addition, the role and regulation of ZIP4, a zinc transporter, have been studied in the context of extracellular zinc transporting. Factors other than zinc with ZIP4 regulatory effects are essentially unknown. ZIP4 expression and its regulation in epithelial ovarian cancer cells was assessed by immunoblotting, quantitative PCR, or immunohistochemistry staining in human ovarian tissues. Cancer stem cell-related activities were examined to evaluate the role of ZIP4 in human high-grade serous ovarian cancer cells in vitro and in vivo. RNAi and CRISPR techniques were used to knockdown or knockout ZIP4 and related genes. Ovarian cancer tissues overexpressed ZIP4 when compared with normal and benign tissues. ZIP4 knockout significantly reduced several cancer stem cell-related activities in EOC cells, including proliferation, anoikis-resistance, colony-formation, spheroid-formation, drug-resistance, and side-population in vitro. ZIP4-expressing side-population highly expressed known CSC markers ALDH1 and OCT4. ZIP4 knockout dramatically reduced tumorigenesis and ZIP4 overexpression increased tumorigenesis in vivo. In addition, the ZIP4-expressing side-population had the tumor initiating activity. Moreover, the oncolipid lysophosphatic acid effectively up-regulated ZIP4 expression via the nuclear receptor peroxisome proliferator-activated receptor gamma and lysophosphatic acid 's promoting effects in cancer stem cell-related activities in HGSOC cells was at least partially mediated by ZIP4 in an extracellular zinc-independent manner. Our critical data imply that ZIP4 is a new and important cancer stem cell regulator in ovarian cancer. Our data also provide an innovative interpretation for the apparent disconnection between low levels of zinc and up-regulation of ZIP4 in ovarian cancer tissues.

Exploiting the ZIP4 homologue within the wheat Ph1 locus has identified two lines exhibiting homoeologous crossover in wheat-wild relative hybrids

Despite possessing related ancestral genomes, hexaploid wheat behaves as a diploid during meiosis. The wheat Ph1 locus promotes accurate synapsis and crossover of homologous chromosomes. Interspecific hybrids between wheat and wild relatives are exploited by breeders to introgress important traits from wild relatives into wheat, although in hybrids between hexaploid wheat and wild relatives, which possess only homoeologues, crossovers do not take place during meiosis at metaphase I. However, in hybrids between Ph1 deletion mutants and wild relatives, crossovers do take place. A single Ph1 deletion (ph1b) mutant has been exploited for the last 40 years for this activity. We show here that chemically induced mutant lines, selected for a mutation in TaZIP4-B2 within the Ph1 locus, exhibit high levels of homoeologous crossovers when crossed with wild relatives. Tazip4-B2 mutant lines may be more stable over multiple generations, as multivalents causing accumulation of chromosome translocations are less frequent. Exploitation of such Tazip4-B2 mutants, rather than mutants with whole Ph1 locus deletions, may therefore improve introgression of wild relative chromosome segments into wheat.

ZIP4 silencing improves bone loss in pancreatic cancer

Metabolic bone disorders are associated with several types of human cancers. Pancreatic cancer patients usually suffer from severe nutrition deficiency, muscle wasting, and loss of bone mass. We have previously found that silencing of a zinc transporter ZIP4 prolongs the survival and reduces the severity of the cachexia in vivo. However, the role of ZIP4 in the pancreatic cancer related bone loss remains unknown. In this study we investigated the effect of ZIP4 knockdown on the bone structure, composition and mechanical properties of femurs in an orthotopic xenograft mouse model. Our data showed that silencing of ZIP4 resulted in increased bone tissue mineral density, decreased bone crystallinity and restoration of bone strength through the RANK/RANKL pathway. The results further support the impact of ZIP4 on the progression of pancreatic cancer, and suggest its potential significance as a therapeutic target for treating patients with such devastating disease and cancer related disorders.

Zinc Supplementation in a Randomized Controlled Trial Decreased ZIP4 and ZIP8 mRNA Abundance in Peripheral Blood Mononuclear Cells of Adult Women

Zinc plays an integral role in numerous cellular processes including regulation of gene expression. This randomized placebo-controlled trial in adult women evaluated the effects of 20 mg Zn for 23 days. The mRNA abundance of zinc transporters (ZnT1/ZIP3/ZIP4/ZIP8) and metallothionein (MT1) from peripheral blood mononuclear cells was determined by real-time quantitative polymerase chain reaction. In paired samples (n = 6–9), the ZIP4 (P = 0.036) and ZIP8 (P = 0.038) mRNA abundance decreased following zinc supplementation. ZnT1, ZIP3, and MT1 mRNA abundance did not change significantly. The mean ± standard deviation plasma zinc concentration (by inductively coupled plasma mass spectrometry) at baseline was 680 ± 110 μg/L for the zinc group (n = 24) and 741 ± 92 μg/L for the placebo group (n = 23). At endpoint, plasma zinc in the zinc group increased to 735 ± 80 μg/L (P < 0.01) while in the placebo group (717 ± 100 μg/L) it did not change significantly from baseline. The change in mRNA abundance highlights the importance of further investigating ZIP4 and ZIP8 mRNA abundance as potential zinc status biomarkers.

ZIP4 confers resistance to zinc deficiency-induced apoptosis in pancreatic cancer

Emerging evidence implicates the zinc importer ZIP4 as a critical factor that enhances pancreatic cancer proliferation; however, the role of ZIP4 in promoting pancreatic cancer progression by regulating apoptosis requires elucidation. To determine the effect of ZIP4 on apoptosis, we used cell lines where ZIP4 levels were upregulated or silenced in combination with Chelex 100 treatment to deplete intracellular zinc. Pancreatic cancer xenografts derived from those cells were also included. TUNEL and flow cytometry analysis were used to measure apoptosis and western blotting was used to analyze protein expression for PARP and multiple caspases. Cell cycle profiles were examined by flow cytometry. Zinc depletion by Chelex induced more apoptosis of pancreatic cancer cells in comparison to normal medium, where almost no apoptosis was observed. ZIP4 stably overexpressed MIA PaCa-2 (MIA-ZIP4) cells were more resistant to zinc depletion-induced apoptosis compared with vector control. Conversely, AsPC-1 (AsPC-shZIP4) cells with stable knockdown of ZIP4 were more sensitive to zinc deficiency than control. Resistance to apoptosis mediated by ZIP4 was accomplished by the caspase pathway. In vivo data also confirmed that ZIP4 overexpressed xenografts showed less apoptosis than controls. Cell cycle profiles indicate that silencing of ZIP4 leads to decreased cell population in S phase and G 0/G 1 arrest. These results described a previously uncharacterized role of ZIP4 in apoptosis resistance and elucidated a novel pathway through which ZIP4 regulates pancreatic cancer growth. This research provides additional evidence for ZIP4 and related signaling cascade as a molecular target for therapeutic intervention in pancreatic cancer.

ZIP4, a novel determinant of tumor invasion in hepatocellular carcinoma, contributes to tumor recurrence after liver transplantation

BACKGROUND AND PURPOSE

Recently, evidence that Zinc transporter ZRT/IRT-like protein 4 (ZIP4) is involved in invasiveness and apoptosis has emerged in pancreatic cancer and prostate cancer. Our aim was to assess the role of ZIP4 in invasiveness, migration and apoptosis of hepatocellular carcinoma (HCC). The prognostic value of ZIP4 in HCC after liver transplantation was evaluated.

METHODS

The role of ZIP4 in HCC was investigated by overexpressing ZIP4 in BEL7402 and HepG2 cells and inhibiting ZIP4 in HuH-7 and HepG2 cells, using overexpression and shRNA plasmids in vitro studies. Immunohistochemical analysis was used to evaluate ZIP4 expression in HCC tissues from 60 patients undergoing liver transplantation, 36 cirrhotic tissue samples, and 6 normal tissue samples. Prognostic significance was assessed using the Kaplan-Meier method and the log-rank test.

RESULTS

Specific suppression of ZIP4 reduced cell migration and invasiveness, whereas ZIP4 overexpression caused increases in cell migration and invasiveness. Furthermore, overexpression of ZIP4 resulted in increased expression of pro-metastatic genes (MMP-2, MMP-9) and decreased expression of pro-apoptotic genes (caspase-3, caspase-9, Bax). In contrast, suppression of ZIP4 resulted in an opposite effect. ZIP4 was more highly expressed in tumor tissues than non-tumor tissues (P < 0.0001). ZIP4 expression was significantly associated with tumor recurrence (P = 0.002), tumor node metastasis stage (P = 0.044), Child-Turcotte-Pugh score (P = 0.042), and tumor size (P = 0.022). Univariate analysis showed that ZIP4 expression was significantly associated with overall survival (P = 0.020) and tumor-free survival (P = 0.049). Multivariate analysis revealed that ZIP4 was an independent predictor of overall survival (P = 0.037) after liver transplantation.

CONCLUSIONS

ZIP4 could promote migration, invasiveness, and suppress apoptosis in hepatocellular carcinoma, and represent a novel predictor of poor prognosis and therapeutic target for patients with HCC who undergo liver transplantation.

A novel epigenetic CREB-miR-373 axis mediates ZIP4-induced pancreatic cancer growth

Changes in the intracellular levels of the essential micronutrient zinc have been implicated in multiple diseases including pancreatic cancer; however, the molecular mechanism is poorly understood. Here, we report a novel mechanism where increased zinc mediated by the zinc importer ZIP4 transcriptionally induces miR-373 in pancreatic cancer to promote tumour growth. Reporter, expression and chromatin immunoprecipitation assays demonstrate that ZIP4 activates the zinc-dependent transcription factor CREB and requires this transcription factor to increase miR-373 expression through the regulation of its promoter. miR-373 induction is necessary for efficient ZIP4-dependent enhancement of cell proliferation, invasion, and tumour growth. Further analysis of miR-373 in vivo oncogenic function reveals that it is mediated through its negative regulation of TP53INP1, LATS2 and CD44. These results define a novel ZIP4-CREB-miR-373 signalling axis promoting pancreatic cancer growth, providing mechanistic insights explaining in part how a zinc transporter functions in cancer cells and may have broader implications as inappropriate regulation of intracellular zinc levels plays an important role in many other diseases.

ZIP4 is a novel molecular marker for glioma

BACKGROUND

Dysregulated zinc transport has been observed in many cancers. However, the status of zinc homeostasis and the expression profile of zinc transporters in brain and brain tumors have not been reported.

METHODS

The gene profiles of 14 zinc importers (ZIPs) and 10 zinc exporters (ZnTs) in patients with glioma were studied by investigating the association between the zinc transporters and brain tumor characteristics (tumor grade and overall survival time). Three independent cohorts were analyzed to cross-validate the findings: the Chinese Glioma Genome Atlas (CGCA) cohort (n = 186), the US National Cancer Institute Repository for Molecular Brain Neoplasia Data (REMBRANDT) cohort (n = 335), and The University of Texas (UT) cohort (n = 34).

RESULTS

The expression of ZIP3, 4, 8, 14, ZnT5, 6, and 7 were increased, and the expression of ZnT10 was decreased in grade IV gliomas, compared with grade II gliomas. Among all 24 zinc transporters, ZIP4 is most significantly associated with tumor grade and overall survival; this finding is consistent across 2 independent cohorts (CGCA and REMBRANDT) and is partially validated by the third cohort (UT). High ZIP4 expression was significantly associated with higher grade of gliomas and shorter overall survival (hazard ratio = 1.61, 95% confidence interval = 1.02-2.53, P = .040 in CGCA cohort; hazard ratio = 1.32, 95% confidence interval = 1.08-1.61, P = .007 in REMBRANDT cohort).

CONCLUSIONS

Dysregulated expression of zinc transporters is involved in the progression of gliomas. Our results suggest that ZIP4 may serve as a potential diagnostic and prognostic marker for gliomas.