Zinc transporter LIV1: A promising cell surface target for triple negative breast cancer.

Breast cancer is one of the leading causes contributing to the global cancer burden. The triple negative breast cancer (TNBC) molecular subtype accounts for the most aggressive type. Despite progression in therapeutic options and prognosis in breast cancer treatment options, there remains a high rate of distant relapse. With advancements in understanding the role of zinc and zinc carriers in the prognosis and treatment of the disease, the scope of precision treatment/targeted therapy has been expanded. Zinc levels and zinc transporters play a vital role in maintaining cellular homeostasis, tumor surveillance, apoptosis, and immune function. This review focuses on the zinc transporter, LIV1, as an essential target for breast cancer prognosis and emerging treatment options. Previous studies give an insight into the role of LIV1 in fulfilling the most important hallmarks of cancer such as apoptosis, metastasis, invasion, and evading the immune system. Normal tissue expression of LIV1 is limited. Higher expression of LIV1 has been linked to Epithelial-Mesenchymal Transition, histological grade of cancer, and early node metastasis. LIV1 was found to be one of the attractive targets in the therapeutic hunt for TNBCs. TNBCs are an immunogenic breast cancer subtype. As zinc transporters are known to serve as the metabolic gatekeepers of immune cells, this review bridges tumor infiltrating lymphocytes, TNBC and LIV1. In addition, the suitability of LIV1 as an antibody-drug conjugate (Seattle genetics [SGN]-LIV1A) target in TNBC, represents a promising strategy for patients. Early clinical trial results reveal that this novel agent reduces tumor burden by inducing mitotic arrest, immunomodulation, and immunogenic cell death, warranting further investigation of SGN-LIV1A in combination with immuno-oncology agents. Priming the patient's immune response in combination with SGN-LIV1A could eventually change the landscape for the TNBC patient population.

High RhCG expression predicts poor survival and promotes migration and proliferation of gastric cancer via keeping intracellular alkaline.

Advanced gastric cancer (GC) is aggressive with a high mortality rate. Rhesus family, C glycoprotein (RhCG) participates in tumor progression in many cancers, however its function in GC is still unknown. Here, we showed that RhCG was overexpressed in GC tissues at mRNA (P = 0.036) and protein levels (P < 0.05) compared with normal tissues. High RhCG level was correlated with poor differentiation (P = 0.037), TNM stage (P < 0.001), high HER-2 level (P = 0.018) and worse prognosis (P < 0.001). Cox proportional hazard model indicated that RhCG level was an independent prognostic biomarker. RhCG knockdown significantly decreased pHi and impeded tumor cellular proliferation, migration and invasion and repressed ß-catenin and c-myc expression in GC cells. Moreover, GC cells with high RhCG level had reduced oxaliplatin efficacy suggesting a role for RhCG as a therapeutic target for GC. Our findings revealed a function of RhCG in cancer pathogenesis, invasion and metastasis in human GC. We suggest that RhCG act may as a novel prognostic indicator and a therapeutic target for gastric adenocarcinoma.

The Oral Ferroportin Inhibitor VIT-2763 Improves Erythropoiesis without Interfering with Iron Chelation Therapy in a Mouse Model of ß-Thalassemia.

In ß-thalassemia, ineffective erythropoiesis leads to anemia and systemic iron overload. The management of iron overload by chelation therapy is a standard of care. However, iron chelation does not improve the ineffective erythropoiesis. We recently showed that the oral ferroportin inhibitor VIT-2763 ameliorates anemia and erythropoiesis in the Hbbth3/+ mouse model of ß-thalassemia. In this study, we investigated whether concurrent use of the iron chelator deferasirox (DFX) and the ferroportin inhibitor VIT-2763 causes any pharmacodynamic interactions in the Hbbth3/+ mouse model of ß-thalassemia. Mice were treated with VIT-2763 or DFX alone or with the combination of both drugs once daily for three weeks. VIT-2763 alone or in combination with DFX improved anemia and erythropoiesis. VIT-2763 alone decreased serum iron and transferrin saturation (TSAT) but was not able to reduce the liver iron concentration. While DFX alone had no effect on TSAT and erythropoiesis, it significantly reduced the liver iron concentration alone and in the presence of VIT-2763. Our results clearly show that VIT-2763 does not interfere with the iron chelation efficacy of DFX. Furthermore, VIT-2763 retains its beneficial effects on improving ineffective erythropoiesis when combined with DFX in the Hbbth3/+ mouse model. In conclusion, co-administration of the oral ferroportin inhibitor VIT-2763 and the iron chelator DFX is feasible and might offer an opportunity to improve both ineffective erythropoiesis and iron overload in ß-thalassemia.

The Arabidopsis phosphatase PP2C49 negatively regulates salt tolerance through inhibition of AtHKT1;1.

Type 2C protein phosphatases (PP2Cs) are the largest protein phosphatase family. PP2Cs dephosphorylate substrates for signaling in Arabidopsis, but the functions of most PP2Cs remain unknown. Here, we characterized PP2C49 (AT3G62260, a Group G PP2C), which regulates Na+ distribution under salt stress and is localized to the cytoplasm and nucleus. PP2C49 was highly expressed in root vascular tissues and its disruption enhanced plant tolerance to salt stress. Compared with wild type, the pp2c49 mutant contained more Na+ in roots but less Na+ in shoots and xylem sap, suggesting that PP2C49 regulates shoot Na+ extrusion. Reciprocal grafting revealed a root-based mechanism underlying the salt tolerance of pp2c49. Systemic Na+ distribution largely depends on AtHKT1;1 and loss of function of AtHKT1;1 in the pp2c49 background overrode the salt tolerance of pp2c49, resulting in salt sensitivity. Furthermore, compared with plants overexpressing PP2C49 in the wild-type background, plants overexpressing PP2C49 in the athtk1;1 mutant background were sensitive to salt, like the athtk1;1 mutants. Moreover, protein-protein interaction and two-voltage clamping assays demonstrated that PP2C49 physically interacts with AtHKT1;1 and inhibits the Na+ permeability of AtHKT1;1. This study reveals that PP2C49 negatively regulates AtHKT1;1 activity and thus determines systemic Na+ allocation during salt stress.

Drosophila ZnT1 is essential in the intestine for dietary zinc absorption.

Zinc is an essential trace element and participates in a variety of biological processes. ZnT (SLC30) family members are generally responsible for zinc efflux across the membrane regulating zinc homeostasis. In mammals, the only predominantly plasma membrane resident ZnT has been reported to be ZnT1, and ZnT1-/ZnT1- mice die at the embryonic stage. In Drosophila, knock down of ZnT1 homologue (dZnT1//ZnT63C/CG17723) results in growth arrest under zinc-limiting conditions. To investigate the essentiality of dZnT1 for zinc homeostasis, as well as its role in dietary zinc uptake especially under normal physiological conditions, we generated dZnT1 mutants by the CRISPER/Cas9 method. Homozygous mutant dZnT1 is lethal, with substantial zinc accumulation in the iron cell region, posterior midgut as well as gastric caeca. Expression of human ZnT1 (hZnT1), in the whole body or in the entire midgut, fully rescued the dZnT1 mutant lethality, whereas tissue-specific expression of hZnT1 in the iron cell region and posterior midgut partially rescued the developmental defect of the dZnT1 mutant. Supplementation of zinc together with clioquinol or hinokitiol conferred a limited but observable rescue upon dZnT1 loss. Our work demonstrated the absolute requirement of dZnT1 in Drosophila survival and indicated that the most essential role of dZnT1 is in the gut.

Salmonella effector SpvB interferes with intracellular iron homeostasis via regulation of transcription factor NRF2.

Iron is a necessary nutrient for humans and nearly all bacterial species. During Salmonella infection, macrophages limit the availability of iron to intracellular pathogens in one of the central components of nutritional immunity. However, Salmonella also have mechanisms to interfere with the antimicrobial effect of host iron withdrawal and meet their own nutrient requirements by scavenging iron from the host. Here, we provide what is, to our knowledge, the first report that SpvB, a pSLT-encoded cytotoxic protein whose function is associated with the intracellular stage of salmonellosis, perturbs macrophage iron metabolism, thereby facilitating Salmonella survival and intracellular replication. In investigating the underlying mechanism, we observed that the Salmonella effector SpvB down-regulated nuclear factor erythroid-derived 2-related factor 2 (NRF2), and its C-terminal domain was necessary and sufficient for NRF2 degradation via the proteasome pathway. Decreased NRF2 expression in the nucleus resulted in a decrease in its transcriptional target ferroportin, encoding the sole macrophage iron exporter, thus ultimately decreasing iron efflux and increasing the intracellular iron content. Additionally, SpvB contributes to the pathogenesis of Salmonella including severe serum hypoferremia, increased splenic and hepatic bacterial burden, and inflammatory injury in vivo. Together, our observations uncovered a novel contribution of SpvB to Salmonella pathology via interference with host intracellular iron metabolism.-Yang, S., Deng, Q., Sun, L., Dong, K., Li, Y., Wu, S., Huang, R. Salmonella effector SpvB interferes with intracellular iron homeostasis via regulation of transcription factor NRF2.

Ferroportin inhibition attenuates plasma iron, oxidant stress, and renal injury following red blood cell transfusion in guinea pigs.

BACKGROUND: Red blood cell (RBC) transfusions result in the sequestration and metabolism of storage-damaged RBCs within the spleen and liver. These events are followed by increased plasma iron concentrations that can contribute to oxidant stress and cellular injury. We hypothesized that administration of a ferroportin inhibitor (FPN-INH) immediately after acute RBC exchange transfusion could attenuate posttransfusion circulatory compartment iron exposure, by retaining iron in spleen and hepatic macrophages. STUDY DESIGN AND METHODS: Donor guinea pig blood was leukoreduced, and RBCs were preserved at 4°C. Recipient guinea pigs (n = 5/group) were exchange transfused with donor RBCs after refrigerator preservation and dosed intravenously with a small-molecule FPN-INH. Groups included transfusion with vehicle (saline), 5 mg/kg or 25 mg/kg FPN-INH. A time course of RBC morphology, plasma non-transferrin-bound iron (NTBI) and plasma hemoglobin (Hb) were evaluated. End-study spleen, liver, and kidney organ iron levels, as well as renal tissue oxidation and injury, were measured acutely (24-hr after transfusion). RESULTS: RBC transfusion increased plasma NTBI, with maximal concentrations occurring 8 hours after transfusion. Posttransfusion iron accumulation resulted in tubule oxidation and acute kidney injury. FPN inhibition increased spleen and liver parenchymal/macrophage iron accumulation, but attenuated plasma NTBI, and subsequent renal tissue oxidation/injury. CONCLUSION: In situations of acute RBC transfusion, minimizing circulatory NTBI exposure by FPN inhibition may attenuate organ-specific adverse consequences of iron exposure.

Oral ferroportin inhibitor VIT-2763: First-in-human, phase 1 study in healthy volunteers.

Restriction of iron availability by ferroportin inhibition is a novel approach to treating non-transfusion-dependent thalassemia (ß-thalassemia intermedia). This first-in-human, Phase I study (https://www.clinicaltrialsregister.eu; EudraCT no. 2017-003395-31) assessed the safety, tolerability, pharmacokinetics and pharmacodynamics of single- and multiple-ascending doses (SAD and MAD) of the oral ferroportin inhibitor, VIT-2763, in healthy volunteers. Participants received VIT-2763 5/15/60/120/240 mg or placebo in the SAD phase and VIT-2763 60/120 mg once daily, VIT-2763 60/120 mg twice daily, or placebo for 7 days in the MAD phase. Seventy-two participants completed treatment. VIT-2763 was well tolerated and demonstrated a similar safety profile to the placebo. There were no serious or severe adverse events, or discontinuations due to adverse events. VIT-2763 absorption was relatively fast, with detectable levels 15 to 30 minutes post-dose. Following multiple dosing there was no apparent change in absorption and accumulation was minimal. Mean elimination half-life was 1.9 to 5.3 hours following single dosing, and 2.1 to 3.8 hours on Day 1 and 2.6 to 5.3 hours on Day 7, following repeated dosing. There was a temporary decrease in mean serum iron levels with VIT-2763 single doses ≥60 mg and all multiple doses; mean calculated transferrin saturation (only assessed following multiple dosing) also temporarily decreased. A shift in mean serum hepcidin peaks followed administration of all iron-lowering doses of VIT-2763. This effect was less pronounced after 7 days of multiple dosing (aside from with 120 mg once daily). These results support the initiation of clinical studies in patients with non-transfusion-dependent thalassemia and documented iron overload due to ineffective erythropoiesis.

Ascorbate inducible N259 glycans on prolyl 4-hydroxylase subunit α1 promote hydroxylation and secretion of type I collagen.

Ascorbic acid (vitamin C, VC) increases the secretion of mature collagen by promoting the activity of prolyl 4-hydroxylase subunit α 1 (P4HA1). To explore the mechanism involved, we investigated the role of N-linked glycosylation, which can regulate enzyme activity. P4HA1 has two glycosylation sites, Asn (N) 113 and N259. Our studies show that glycosylation of N259, but not N113, by STT3B and magnesium transporter 1 (MAGT1) is augmented by VC. N259 glycosylation on P4HA1 correlates with enhanced pepsin-resistant collagen 1α2 secretion. Downregulation of Stt3b and Magt1 reduces N259 glycans on P4HA1. In collagen 1α2 purified from Stt3b-silenced fibroblasts, decreased hydroxylation is found at five specific proline residues, while significantly increased hydroxylation is noted at two proline residues. Similarly, in collagen 1α1, reduced proline hydroxylation is detected at eight sites and increased proline hydroxylation is found at four sites. These results suggest that N-linked glycosylation of P4HA1 can direct hydroxylation at specific proline residues and affect collagen maturation.

Towards an Integral Therapeutic Protocol for Breast Cancer Based upon the New H+-Centered Anticancer Paradigm of the Late Post-Warburg Era.

A brand new approach to the understanding of breast cancer (BC) is urgently needed. In this contribution, the etiology, pathogenesis, and treatment of this disease is approached from the new pH-centric anticancer paradigm. Only this unitarian perspective, based upon the hydrogen ion (H+) dynamics of cancer, allows for the understanding and integration of the many dualisms, confusions, and paradoxes of the disease. The new H+-related, wide-ranging model can embrace, from a unique perspective, the many aspects of the disease and, at the same time, therapeutically interfere with most, if not all, of the hallmarks of cancer known to date. The pH-related armamentarium available for the treatment of BC reviewed here may be beneficial for all types and stages of the disease. In this vein, we have attempted a megasynthesis of traditional and new knowledge in the different areas of breast cancer research and treatment based upon the wide-ranging approach afforded by the hydrogen ion dynamics of cancer. The concerted utilization of the pH-related drugs that are available nowadays for the treatment of breast cancer is advanced.

Biochemical characterization and chemical inhibition of PfATP4-associated Na+-ATPase activity in Plasmodium falciparum membranes.

The antimalarial activity of chemically diverse compounds, including the clinical candidate cipargamin, has been linked to the ATPase PfATP4 in the malaria-causing parasite Plasmodium falciparum The characterization of PfATP4 has been hampered by the inability thus far to achieve its functional expression in a heterologous system. Here, we optimized a membrane ATPase assay to probe the function of PfATP4 and its chemical sensitivity. We found that cipargamin inhibited the Na+-dependent ATPase activity present in P. falciparum membranes from WT parasites and that its potency was reduced in cipargamin-resistant PfATP4-mutant parasites. The cipargamin-sensitive fraction of membrane ATPase activity was inhibited by all 28 of the compounds in the "Malaria Box" shown previously to disrupt ion regulation in P. falciparum in a cipargamin-like manner. This is consistent with PfATP4 being the direct target of these compounds. Characterization of the cipargamin-sensitive ATPase activity yielded data consistent with PfATP4 being a Na+ transporter that is sensitive to physiologically relevant perturbations of pH, but not of [K+] or [Ca2+]. With an apparent Km for ATP of 0.2 mm and an apparent Km for Na+ of 16-17 mm, the protein is predicted to operate at below its half-maximal rate under normal physiological conditions, allowing the rate of Na+ efflux to increase in response to an increase in cytosolic [Na+]. In membranes from a cipargamin-resistant PfATP4-mutant line, the apparent Km for Na+ is slightly elevated. Our study provides new insights into the biochemical properties and chemical sensitivity of an important new antimalarial drug target.

microRNA-199a-5p suppresses glioma progression by inhibiting MAGT1.

microRNAs (miRNAs) can function as a tumor suppressor or oncogenic genes in human cancers. Alternation expression of miR-199a-5p has been revealed in several human cancers. However, its expression pattern and biological roles in glioma remain unclear. Expression levels of miR-199a-5p in glioma were evaluated at first. The effects of miR-199a-5p expression on cell proliferation, migration, and invasion were investigated using the MTT assay, wound-healing assay, and transwell invasion assay. The expression of miR-199a-5p was found to be reduced in glioma cell lines. Overexpression of miR-199a-5p inhibits glioma cell proliferation, migration, and invasion in vitro. Furthermore, the target of miR-199a-5p was predicted by TargetScan and validated by luciferase activity reporter assay. We found magnesium transporter 1 (MAGT1) was a direct target of miR-199a-5p. Overexpression of MAGT1 reversed the effects of miR-199a-5p on glioma cell behaviors. Taken together, our study revealed that miR-199a-5p and MAGT1 have the potential to be used as a biomarker for glioma.

Leishmania donovani inhibits ferroportin translation by modulating FBXL5-IRP2 axis for its growth within host macrophages.

Hepcidin mediated ferroportin (Fpn) degradation in macrophages is a well adopted strategy to limit iron availability towards invading pathogens. Leishmania donovani (LD), a protozoan parasite, resides within macrophage and competes with host for availing iron. Using in vitro and in vivo model of infection, we reveal that LD decreases Fpn abundance in host macrophages by hepcidin independent mechanism. Unaffected level of Fpn-FLAG in LD infected J774 macrophage confirms that Fpn down-regulation is not due its degradation. While increased Fpn mRNA but decreased protein expression in macrophages suggests blocking of Fpn translation by LD infection that is confirmed by 35 S-methionine labelling assay. We further reveal that LD blocks Fpn translation by induced binding of iron regulatory proteins (IRPs) to the iron responsive element present in its 5'UTR. Supershift analysis provides evidence of involvement of IRP2 particularly during in vivo infection. Accordingly, a significant increase in IRP2 protein expression with simultaneous decrease in its stability regulator F-box and leucine-rich repeat Protein 5 (FBXL5) is detected in splenocytes of LD-infected mice. Increased intracellular growth due to compromised expressions of Fpn and FBXL5 by specific siRNAs reveals that LD uses a novel strategy of manipulating IRP2-FBXL5 axis to inhibit host Fpn expression.

Targeting the hepcidin-ferroportin pathway in anaemia of chronic kidney disease.

AIMS: Erythropoiesis-stimulating agents used to treat anaemia in patients with chronic kidney disease (CKD) have been associated with cardiovascular adverse events. Hepcidin production, controlled by bone morphogenic protein 6 (BMP6), regulates iron homeostasis via interactions with the iron transporter, ferroportin. High hepcidin levels are thought to contribute to increased iron sequestration and subsequent anaemia in CKD patients. To investigate alternative therapies to erythropoiesis-stimulating agents for CKD patients, monoclonal antibodies, LY3113593 and LY2928057, targeting BMP6 and ferroportin respectively, were tested in CKD patients. METHODS: Preclinical in vitro/vivo data and clinical data in healthy subjects and CKD patients were used to illustrate the translation of pharmacological properties of LY3113593 and LY2928057, highlighting the novelty of targeting these nodes within the hepcidin-ferroportin pathway. RESULTS: LY2928057 bound ferroportin and blocked interactions with hepcidin, allowing iron efflux, leading to increased serum iron and transferrin saturation levels and increased hepcidin in monkeys and humans. In CKD patients, LY2928057 led to slower haemoglobin decline and reduction in ferritin (compared to placebo). Serum iron increase was (mean [90% confidence interval]) 1.98 [1.46-2.68] and 1.36 [1.22-1.51] fold-relative to baseline following LY2928057 600 mg and LY311593 150 mg respectively in CKD patients. LY3113593 specifically blocked BMP6 binding to its receptor and produced increases in iron and transferrin saturation and decreases in hepcidin preclinically and clinically. In CKD patients, LY3113593 produced an increase in haemoglobin and reduction in ferritin (compared to placebo). CONCLUSION: LY3113593 and LY2928057 pharmacological effects (serum iron and ferritin) were translated from preclinical-to-clinical development. Such interventions may lead to new CKD anaemia treatments.

Activation and Inhibition of Sodium-Hydrogen Exchanger Is a Mechanism That Links the Pathophysiology and Treatment of Diabetes Mellitus With That of Heart Failure.

The mechanisms underlying the progression of diabetes mellitus and heart failure are closely intertwined, such that worsening of one condition is frequently accompanied by worsening of the other; the degree of clinical acceleration is marked when the 2 coexist. Activation of the sodium-hydrogen exchanger in the heart and vasculature (NHE1 isoform) and the kidneys (NHE3 isoform) may serve as a common mechanism that links both disorders and may underlie their interplay. Insulin insensitivity and adipokine abnormalities (the hallmarks of type 2 diabetes mellitus) are characteristic features of heart failure; conversely, neurohormonal systems activated in heart failure (norepinephrine, angiotensin II, aldosterone, and neprilysin) impair insulin sensitivity and contribute to microvascular disease in diabetes mellitus. Each of these neurohormonal derangements may act through increased activity of both NHE1 and NHE3. Drugs used to treat diabetes mellitus may favorably affect the pathophysiological mechanisms of heart failure by inhibiting either or both NHE isoforms, and drugs used to treat heart failure may have beneficial effects on glucose tolerance and the complications of diabetes mellitus by interfering with the actions of NHE1 and NHE3. The efficacy of NHE inhibitors on the risk of cardiovascular events may be enhanced when heart failure and glucose intolerance coexist and may be attenuated when drugs with NHE inhibitory actions are given concomitantly. Therefore, the sodium-hydrogen exchanger may play a central role in the interplay of diabetes mellitus and heart failure, contribute to the physiological and clinical progression of both diseases, and explain certain drug-drug and drug-disease interactions that have been reported in large-scale randomized clinical trials.

RHCG suppresses cervical cancer progression through inhibiting migration and inducing apoptosis regulated by TGF-ß1.

Cervical cancer is the second commonest cancer among women in the worldwide, and the majority cause of death in various countries, highlighting the importance of investigating new therapeutic targets. Rh family, C glycoprotein (RHCG) belongs to the Rhesus (Rh) family and was first identified as Rh blood group antigens. It has been confirmed to function in cancer progression, including prostate cancer and esophageal squamous cell carcinoma. However, its role in cervical cancer has never been explored. The present study indicated that RHCG was down-regulated in cervical cancers compared to that in normal cervical tissues, and further decreased in cervical cancer cell lines. Functionally, RHCG overexpression reduced cervical cancer cell proliferation and migration, as evidenced by the decreased transforming growth factor (TGF)-ß1, matrix metalloproteinase (MMP)-2 and MMP-9 expressions in cancer cells; however, an opposite effect was observed when RHCG was knocked down. Further, increase of RHCG markedly induced apoptosis in cervical cancer cells by improving the cleavage of Caspase-3 and poly (ADP-Ribose) polymerase (PARP). And cells transfected with RHCG siRNA exhibited a notable reduction of cleaved Caspase-3 and PARP. Moreover, nucleus nuclear factor-κB (NF-κB) and whole cell xIPA expressions were markedly reduced by over-expressing RHCG. Conversely, suppressing RHCG elevated NF-κB activation and xIPA expression in cervical cancer cells. Notably, we found that TGF-ß1 treatment could abolish the effects of RHCG over-expression on the reduction of cell migration and enhancement of apoptosis in cervical cancer cells. Over-expressing RHCG-reduced NF-κB activation and xIPA expression were also abrogated by TGF-ß1 pre-treatment. Additionally, enhancing NF-κB activity could restore xIPA expressions and decrease apoptotic response in cervical cancer cells over-expressing RHCG. In vivo, we also found that RHCG over-expression reduced cervical tumor growth through the same signaling pathways as we found in vitro. Therefore, RHCG may be a potential prognostic biomarker and therapeutic target for human cervical cancer.

Merestinib blocks Mnk kinase activity in acute myeloid leukemia progenitors and exhibits antileukemic effects in vitro and in vivo.

Mitogen-activated protein kinase interacting protein kinases (Mnks) play important roles in the development and progression of acute myeloid leukemia (AML) by regulating eukaryotic translation initiation factor 4E (eIF4E) activation. Inhibiting Mnk1/2-induced phosphorylation of eIF4E may represent a unique approach for the treatment of AML. We provide evidence for antileukemic effects of merestinib, an orally bioavailable multikinase inhibitor with suppressive effects on Mnk activity. Our studies show that merestinib effectively blocks eIF4E phosphorylation in AML cells and suppresses primitive leukemic progenitors from AML patients in vitro and in an AML xenograft model in vivo. Our findings provide evidence for potent preclinical antileukemic properties of merestinib and support its clinical development for the treatment of patients with AML.

Suppression of ferroportin expression by cadmium stimulates proliferation, EMT, and migration in triple-negative breast cancer cells.

Cadmium (Cd) has been linked to a variety of cancers, including breast cancer; however, the molecular mechanism of its carcinogenic activity is not fully understood. To this end, the present study investigated the roles of ferroportin (FPN), a prognostic marker of breast cancer, in Cd-induced stimulation of cell proliferation and cell migration. Triple-negative MDA-MB-231 cells were treated with 1-3 µM Cd. The cells exhibited significant reduction in FPN expression and concomitant increase in iron concentration. Cells treated with Cd for 8 weeks displayed elevated proliferative and migratory activities which were inversely related with FPN expression. Reduced FPN expression also resulted in EMT as indicated by an increase in the expression of E-cadherin, and a decrease in the expression of N-cadherin, Twist and Slug. Further investigation revealed that Cd suppressed FPN expression at least partially by activating TGF-ß, a known regulator of FPN expression. Taken together, these results indicate that Cd-induced stimulation of MDA-MB-231 cell proliferation, EMT, and migration is brought about by suppression of FPN expression and associated disruption of iron homeostasis.

Selective Assembly of Na,K-ATPase α2ß2 Heterodimers in the Heart: DISTINCT FUNCTIONAL PROPERTIES AND ISOFORM-SELECTIVE INHIBITORS.

The Na,K-ATPase α2 subunit plays a key role in cardiac muscle contraction by regulating intracellular Ca2+, whereas α1 has a more conventional role of maintaining ion homeostasis. The ß subunit differentially regulates maturation, trafficking, and activity of α-ß heterodimers. It is not known whether the distinct role of α2 in the heart is related to selective assembly with a particular one of the three ß isoforms. We show here by immunofluorescence and co-immunoprecipitation that α2 is preferentially expressed with ß2 in T-tubules of cardiac myocytes, forming α2ß2 heterodimers. We have expressed human α1ß1, α2ß1, α2ß2, and α2ß3 in Pichia pastoris, purified the complexes, and compared their functional properties. α2ß2 and α2ß3 differ significantly from both α2ß1 and α1ß1 in having a higher K0.5K+ and lower K0.5Na+ for activating Na,K-ATPase. These features are the result of a large reduction in binding affinity for extracellular K+ and shift of the E1P-E2P conformational equilibrium toward E1P. A screen of perhydro-1,4-oxazepine derivatives of digoxin identified several derivatives (e.g. cyclobutyl) with strongly increased selectivity for inhibition of α2ß2 and α2ß3 over α1ß1 (range 22-33-fold). Molecular modeling suggests a possible basis for isoform selectivity. The preferential assembly, specific T-tubular localization, and low K+ affinity of α2ß2 could allow an acute response to raised ambient K+ concentrations in physiological conditions and explain the importance of α2ß2 for cardiac muscle contractility. The high sensitivity of α2ß2 to digoxin derivatives explains beneficial effects of cardiac glycosides for treatment of heart failure and potential of α2ß2-selective digoxin derivatives for reducing cardiotoxicity.

Na(+)/H(+) antiporter (NHE1) and lactate/H(+) symporters (MCTs) in pH homeostasis and cancer metabolism.

The Na(+)/H(+)-exchanger NHE1 and the monocarboxylate transporters MCT1 and MCT4 are crucial for intracellular pH regulation, particularly under active metabolism. NHE1, a reversible antiporter, uses the energy provided by the Na(+) gradient to expel H(+) ions generated in the cytosol. The reversible H(+)/lactate(-) symporters MCT1 and 4 cotransport lactate and proton, leading to the net extrusion of lactic acid in glycolytic tumors. In the first two sections of this article we review important features and remaining questions on the structure, biochemical function and cellular roles of these transporters. We then use a fully-coupled mathematical model to simulate their relative contribution to pH regulation in response to lactate production, as it occurs in highly hypoxic and glycolytic tumor cells. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.