Suppressing Effect of Na+/Ca2+ Exchanger (NCX) Inhibitors on the Growth of Melanoma Cells

Perfluorooctane sulfonate-induced Sertoli cell injury through c-Jun N-terminal kinase: a study by RNA-Seq

Per- and polyfluoroalkyl substances (PFASs) are a family of "forever chemicals" including perfluorooctane sulfonate (PFOS). These toxic chemicals do not break down in the environment or in our bodies. In the human body, PFOS and perfluoroctanoic acid (PFOA) have a half-life (T1/2) of about 4-5 yr so low daily consumption of these chemicals can accumulate in the human body to a harmful level over a long period. Although the use of PFOS in consumer products was banned in the United States in 2022/2023, this forever chemical remains detectable in our tap water and food products. Every American tested has a high level of PFAS in their blood (https://cleanwater.org/pfas-forever-chemicals). In this report, we used a Sertoli cell blood-testis barrier (BTB) model with primary Sertoli cells cultured in vitro with an established functional tight junction (TJ)-permeability barrier that mimicked the BTB in vivo. Treatment of Sertoli cells with PFOS was found to perturb the TJ-barrier, which was the result of cytoskeletal disruption across the cell cytoplasm, disrupting actin and microtubule polymerization. These changes thus affected the proper localization of BTB-associated proteins at the BTB. Using RNA-Seq transcriptome profiling, bioinformatics analysis, and pertinent biochemical and cell biology techniques, it was discovered that PFOS -induced Sertoli cell toxicity through the c-Jun N-terminal kinase (JNK; also known as stress-activated protein kinase, SAPK) and its phosphorylated/active form p-JNK signaling pathway. More importantly, KB-R7943 mesylate (KB), a JNK/p-JNK activator, was capable of blocking PFOS-induced Sertoli cell injury, supporting the notion that PFOS-induced cell injury can possibly be therapeutically managed.NEW & NOTEWORTHY PFOS induces Sertoli cell injury, including disruption of the 1) blood-testis barrier function and 2) cytoskeletal organization, which, in turn, impedes male reproductive function. These changes are mediated by JNK/p-JNK signaling pathway. However, the use of KB-R7943, a JNK/p-JNK activator was capable of blocking PFOS-induced Sertoli cell injury, supporting the possibility of therapeutically managing PFOS-induced reproductive dysfunction.

Identification and validation of calcium extrusion-related genes prognostic signature in colon adenocarcinoma

Background

Disruptions in calcium homeostasis are associated with a wide range of diseases, and play a pivotal role in the development of cancer. However, the construction of prognostic models using calcium extrusion-related genes in colon adenocarcinoma (COAD) has not been well studied. We aimed to identify whether calcium extrusion-related genes serve as a potential prognostic biomarker in the COAD progression.

Methods

We constructed a prognostic model based on the expression of calcium extrusion-related genes (SLC8A1, SLC8A2, SLC8A3, SLC8B1, SLC24A2, SLC24A3 and SLC24A4) in COAD. Subsequently, we evaluated the associations between the risk score calculated by calcium extrusion-related genes and mutation signature, immune cell infiltration, and immune checkpoint molecules. Then we calculated the immune score, stromal score, tumor purity and estimate score using the Estimation of STromal and Immune cells in MAlignant Tumor tissues using Expression data (ESTIMATE) algorithm. The response to immunotherapy was assessed using tumor immune dysfunction and exclusion (TIDE). Finally, colorectal cancer cells migration, growth and colony formation assays were performed in RKO cells with the overexpression or knockdown SLC8A3, SLC24A2, SLC24A3, or SLC24A4.

Results

We found that patients with high risk score of calcium extrusion-related genes tend to have a poorer prognosis than those in the low-risk group. Additionally, patients in high-risk group had higher rates of KRAS mutations and lower MUC16 mutations, implying a strong correlation between KRAS and MUC16 mutations and calcium homeostasis in COAD. Moreover, the high-risk group showed a higher infiltration of regulatory T cells (Tregs) in the tumor microenvironment. Finally, our study identified two previously unreported model genes (SLC8A3 and SLC24A4) that contribute to the growth and migration of colorectal cancer RKO cells.

Conclusions

Altogether, we developed a prognostic risk model for predicting the prognosis of COAD patients based on the expression profiles of calcium extrusion-related genes, Furthermore, we validated two previously unreported tumor suppressor genes (SLC8A3 and SLC24A4) involved in colorectal cancer progression.

NCX1/Ca2+ promotes autophagy and decreases bortezomib activity in multiple myeloma through non-canonical NFκB signaling pathway

Although bortezomib (BTZ) is the cornerstone of anti-multiple myeloma (MM) therapy, the inevitable primary and secondary drug resistance still seriously affects the prognosis of patients. New treatment strategies are in need. Sodium-calcium exchanger 1 (NCX1) is a calcium-permeable ion transporter on the membrane, and our previous studies showed that low NCX1 confers inferior viability in MM cells and suppressed osteoclast differentiation. However, the effect of NCX1 on BTZ sensitivity of MM and its possible mechanism remain unclear. In this study, we investigated the effect of NCX1 on BTZ sensitivity in MM, focusing on cellular processes of autophagy and cell viability. Our results provide evidence that NCX1 expression correlates with MM disease progression and low NCX1 expression increases BTZ sensitivity. NCX1/Ca2+ triggered autophagic flux through non-canonical NFκB pathway in MM cells, leading to attenuated the sensitivity of BTZ. Knockdown or inhibition of NCX1 could potentiate the anti-MM activity of BTZ in vitro and vivo, and inhibition of autophagy sensitized NCX1-overexpressing MM cells to BTZ. In general, this work implicates NCX1 as a potential therapeutic target in MM with BTZ resistance and provides novel mechanistic insights into its vital role in combating BTZ resistance.

Application of calcium overload-based ion interference therapy in tumor treatment: strategies, outcomes, and prospects

Low selectivity and tumor drug resistance are the main hinderances to conventional radiotherapy and chemotherapy against tumor. Ion interference therapy is an innovative anti-tumor strategy that has been recently reported to induce metabolic disorders and inhibit proliferation of tumor cells by reordering bioactive ions within the tumor cells. Calcium cation (Ca2+) are indispensable for all physiological activities of cells. In particular, calcium overload, characterized by the abnormal intracellular Ca2+ accumulation, causes irreversible cell death. Consequently, calcium overload-based ion interference therapy has the potential to overcome resistance to traditional tumor treatment strategies and holds promise for clinical application. In this review, we 1) Summed up the current strategies employed in this therapy; 2) Described the outcome of tumor cell death resulting from this therapy; 3) Discussed its potential application in synergistic therapy with immunotherapy.

Suppression of Metastatic Ovarian Cancer Cells by Bepridil, a Calcium Channel Blocker

Although surgery followed by platinum-based therapy is effective as a standard treatment in the early stages of ovarian cancer, the majority of cases are diagnosed at advanced stages, leading to poor prognosis. Thus, the identification of novel therapeutic drugs is needed. In this study, we assessed the effectiveness of bepridil-a calcium channel blocker-in ovarian cancer cells using two cell lines: SKOV-3, and SKOV-3-13 (a highly metastatic clone of SKOV-3). Treatment of these cell lines with bepridil significantly reduced cell viability, migration, and invasion. Notably, SKOV-3-13 was more sensitive to bepridil than SKOV-3. The TGF-β1-induced epithelial-mesenchymal transition (EMT)-like phenotype was reversed by treatment with bepridil in both cell lines. Consistently, expression levels of EMT-related markers, including vimentin, β-catenin, and Snail, were also substantially decreased by the treatment with bepridil. An in vivo mouse xenograft model was used to confirm these findings. Tumor growth was significantly reduced by bepridil treatment in SKOV-3-13-inoculated mice, and immunohistochemistry showed consistently decreased expression of EMT-related markers. Our findings are the first to report anticancer effects of bepridil in ovarian cancer, and they suggest that bepridil holds significant promise as an effective therapeutic agent for targeting metastatic ovarian cancer.

Inhibition of Voltage-Gated Na+ Currents Exerted by KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea), an Inhibitor of Na+-Ca2+ Exchanging Process

KB-R7943, an isothiourea derivative, has been recognized as an inhibitor in the reverse mode of the Na⁺-Ca²⁺ exchanging process. This compound was demonstrated to prevent intracellular Na⁺-dependent Ca²⁺ uptake in intact cells; however, it is much less effective at preventing extracellular Na⁺-dependent Ca²⁺ efflux. Therefore, whether or how this compound may produce any perturbations on other types of ionic currents, particularly on voltage-gated Na⁺ current (I_Na), needs to be further studied. In this study, the whole-cell current recordings demonstrated that upon abrupt depolarization in pituitary GH₃ cells, the exposure to KB-R7943 concentration-dependently depressed the transient (I_Na(T)) or late component (I_Na(L)) of I_Na with an IC₅₀ value of 11 or 0.9 μM, respectively. Likewise, the dissociation constant for the KB-R7943-mediated block of I_Na on the basis of a minimum reaction scheme was estimated to be 0.97 μM. The presence of benzamil or amiloride could suppress the I_Na(L) magnitude. The instantaneous window Na⁺ current (I_Na(W)) activated by abrupt ascending ramp voltage (V_ramp) was suppressed by adding KB-R7943; however, subsequent addition of deltamethrin or tefluthrin (Tef) effectively reversed KB-R7943-inhibted I_Na(W). With prolonged duration of depolarizing pulses, the I_Na(L) amplitude became exponentially decreased; moreover, KB-R7943 diminished I_Na(L) magnitude. The resurgent Na⁺ current (I_Na(R)) evoked by a repolarizing V_ramp was also suppressed by adding this compound; moreover, subsequent addition of ranolazine or Tef further diminished or reversed, respectively, its reduction in I_Na(R) magnitude. The persistent Na⁺ current (I_Na(P)) activated by sinusoidal voltage waveform became enhanced by Tef; however, subsequent application of KB-R7943 counteracted Tef-stimulated I_Na(P). The docking prediction reflected that there seem to be molecular interactions of this molecule with the hNa_V1.2 or hNa_V1.7 channels. Collectively, this study highlights evidence showing that KB-R7943 has the propensity to perturb the magnitude and gating kinetics of I_Na (e.g., I_Na(T), I_Na(L), I_Na(W), I_Na(R), and I_Na(P)) and that the Na_V channels appear to be important targets for the in vivo actions of KB-R7943 or other relevant compounds.

Structure-Based Function and Regulation of NCX Variants: Updates and Challenges

The plasma-membrane homeostasis Na⁺/Ca²⁺ exchangers (NCXs) mediate Ca²⁺ extrusion/entry to dynamically shape Ca²⁺ signaling/in biological systems ranging from bacteria to humans. The NCX gene orthologs, isoforms, and their splice variants are expressed in a tissue-specific manner and exhibit nearly 10⁴-fold differences in the transport rates and regulatory specificities to match the cell-specific requirements. Selective pharmacological targeting of NCX variants could benefit many clinical applications, although this intervention remains challenging, mainly because a full-size structure of eukaryotic NCX is unavailable. The crystal structure of the archaeal NCX_Mj, in conjunction with biophysical, computational, and functional analyses, provided a breakthrough in resolving the ion transport mechanisms. However, NCX_Mj (whose size is nearly three times smaller than that of mammalian NCXs) cannot serve as a structure-dynamic model for imitating high transport rates and regulatory modules possessed by eukaryotic NCXs. The crystal structures of isolated regulatory domains (obtained from eukaryotic NCXs) and their biophysical analyses by SAXS, NMR, FRET, and HDX-MS approaches revealed structure-based variances of regulatory modules. Despite these achievements, it remains unclear how multi-domain interactions can decode and integrate diverse allosteric signals, thereby yielding distinct regulatory outcomes in a given ortholog/isoform/splice variant. This article summarizes the relevant issues from the perspective of future developments.

NCX1 coupled with TRPC1 to promote gastric cancer via Ca2+/AKT/β-catenin pathway

Plasma membrane Na⁺/Ca²⁺ exchanger 1 (NCX1) is a bidirectional ion transporter to operate in Ca²⁺ entry or exit modes, and TRPC1 is Ca²⁺-permeable channel. Both NCX1 and TRPC1 play critical roles in maintaining cytosolic free Ca²⁺ ([Ca²⁺]_cyt) homeostasis in mammalian cells. Although either TRPC1 channel or Ca²⁺ entry mode of NCX1 is implicated in some tumorigenesis, it has not been explored if a coordination of NCX1 and TRPC1 involves in the pathogenesis of H. pylori-associated human gastric cancer (GC). Here we found the protein expression of NCX1 was significantly enhanced in human GC specimens, which correlated with tumor progression and poor survival in GC patients. TRPC1 and NCX1 were parallelly enhanced, co-localized and bound in human GC cells. By a functional coupling, TRPC1 drives NCX1 to the Ca²⁺ entry mode, raising [Ca²⁺]_cyt in GC cells. Moreover, CaCl₂, H. pylori and their virulence factors all enhanced expressions and activities of NCX1 and TRPC1, and evoked aberrant Ca²⁺ entry to promote proliferation, migration, and invasion of GC cells through AKT/β-catenin pathway. Tumor growth and metastasis also depended on the enhanced expression of NCX1 in subcutaneously xenografted GC mouse model. Overall, our findings indicate that TRPC1/NCX1 coupling may promote H. pylori-associated GC through the Ca²⁺/AKT/β-catenin pathway. Since the Ca²⁺ exit mode and the Ca²⁺ entry mode of NCX1 play different roles under mostly physiological and pathological conditions respectively, targeting TRPC1/NCX1 coupling could be a novel strategy for selectively blocking Ca²⁺ entry mode to potentially treat digestive cancer with less side effect.

Control of Ca2+ and metabolic homeostasis by the Na+/Ca2+ exchangers (NCXs) in health and disease

Spatial and temporal control of calcium (Ca²⁺) levels is essential for the background rhythms and responses of living cells to environmental stimuli. Whatever other regulators a given cellular activity may have, localized and wider scale Ca²⁺ events (sparks, transients, and waves) are hierarchical determinants of fundamental processes such as cell contraction, excitability, growth, metabolism and survival. Different cell types express specific channels, pumps and exchangers to efficiently generate and adapt Ca²⁺ patterns to cell requirements. The Na⁺/Ca²⁺ exchangers (NCXs) in particular contribute to Ca²⁺ homeostasis by buffering intracellular Ca²⁺ loads according to the electrochemical gradients of substrate ions - i.e., Ca²⁺ and sodium (Na⁺) - and under a dynamic control of redundant regulatory processes. An interesting feature of NCX emerges from the strict relationship that connects transporter activity with cell metabolism: on the one hand NCX operates under constant control of ATP-dependent regulatory processes, on the other hand the ion fluxes generated through NCX provide mechanistic support for the Na⁺-driven uptake of glutamate and Ca²⁺ influx to fuel mitochondrial respiration. Proof of concept evidence highlights therapeutic potential of preserving a timed and balanced NCX activity in a growing rate of diseases (including excitability, neurodegenerative, and proliferative disorders) because of an improved ability of stressed cells to safely maintain ion gradients and mitochondrial bioenergetics. Here, we will summarize and review recent works that have focused on the pathophysiological roles of NCXs in balancing the two-way relationship between Ca²⁺ signals and metabolism.