Search Results (15)

In this work, the utilization of calcium and strontium by the (Ca²⁺ + Mg²⁺)ATPase of the basolateral plasma membrane of renal proximal convoluted tubules were compared. [⁹⁰Sr]Sr²⁺ and [⁴⁵Ca]Ca²⁺ uptake by vesicles derived from this membrane were strictly dependent on ATP and Mg²⁺, and no other nucleotide was able to support the transport. Each cation inhibited the uptake of the other one in a purely competitive fashion (the same Vmax; increased K_0.5), without causing a significant change in the influx rate. These results indicate that both cations bind at the same transport site on the enzyme, facing the cytosolic surface of the cell. The K_0.5 for Sr²⁺ obtained for (Sr²⁺ + Mg²⁺)ATPase activity was 13.1 ± 0.2 µM and for Sr²⁺ uptake was 13.4 ± 0.1 µM. They were higher than K_0.5 for Ca²⁺ obtained for (Ca²⁺ + Mg²⁺)ATPase activity (0.42 ± 0.03 µM) and for Ca²⁺ uptake (0.28 ± 0.02 µM). It is postulated that the lower ATPase affinity for Sr²⁺ is associated with greater steric difficulties for the occupation by this cation of the binding and transport sites, as a consequence of its greater crystal ionic radius (1.13 Å for Sr²⁺ against 0.99 Å for Ca²⁺). Full article

The cytosolic calcium concentration ([Ca²⁺]_cyt) in yeast cells is maintained at a low level via the action of different transporters sequestrating these cations in the vacuole. Among them, the vacuolar Ca²⁺ ATPase Pmc1 crucially contributes to this process. Its inactivation in Ogataea yeasts was shown to cause sodium dodecyl sulfate (SDS) hypersensitivity that can be alleviated by the inactivation of the plasma membrane high-affinity Ca²⁺ channel Cch1. Here, we show that SDS at low concentrations induces a rapid influx of external Ca²⁺ into cells, while the plasma membrane remains impermeable for propidium iodide. The inactivation of Pmc1 disturbs efficient adaptation to this activity of SDS. The inactivation of Cch1 partially restores the ability of pmc1 mutant cells to cope with an increased [Ca²⁺]_cyt that correlates with the suppression of SDS hypersensitivity. At the same time, Cch1 is unlikely to be directly involved in SDS-induced Ca²⁺ influx, since its inactivation does not decrease the amplitude of the rapid [Ca²⁺]_cyt elevation in the pmc1-Δ mutant. The obtained data suggest that the effects of CCH1 inactivation on SDS sensitivity and coping with increased [Ca²⁺]_cyt are related to an additional Cch1 function beyond its direct involvement in Ca²⁺ transport. Full article

Identification of alternative attenuation targets of Mycobacterium tuberculosis (Mtb) is pivotal for designing new candidates for live attenuated anti-tuberculosis (TB) vaccines. In this context, the CtpF P-type ATPase of Mtb is an interesting target; specifically, this plasma membrane enzyme is involved in calcium transporting and response to oxidative stress. We found that a mutant of MtbH37Rv lacking ctpF expression (MtbΔctpF) displayed impaired proliferation in mouse alveolar macrophages (MH-S) during in vitro infection. Further, the levels of tumor necrosis factor and interferon-gamma in MH-S cells infected with MtbΔctpF were similar to those of cells infected with the parental strain, suggesting preservation of the immunogenic capacity. In addition, BALB/c mice infected with Mtb∆ctpF showed median survival times of 84 days, while mice infected with MtbH37Rv survived 59 days, suggesting reduced virulence of the mutant strain. Interestingly, the expression levels of ctpF in a mouse model of latent TB were significantly higher than in a mouse model of progressive TB, indicating that ctpF is involved in Mtb persistence in the dormancy state. Finally, the possibility of complementary mechanisms that counteract deficiencies in Ca²⁺ transport mediated by P-type ATPases is suggested. Altogether, our results demonstrate that CtpF could be a potential target for Mtb attenuation. Full article

Genome-wide association studies for severe malaria (SM) have identified 30 genetic variants mostly located in non-coding regions. Here, we aimed to identify potential causal genetic variants located in these loci and demonstrate their functional activity. We systematically investigated the regulatory effect of the SNPs in linkage disequilibrium (LD) with the malaria-associated genetic variants. Annotating and prioritizing genetic variants led to the identification of a regulatory region containing five ATP2B4 SNPs in LD with rs10900585. We found significant associations between SM and rs10900585 and our candidate SNPs (rs11240734, rs1541252, rs1541253, rs1541254, and rs1541255) in a Senegalese population. Then, we demonstrated that both individual SNPs and the combination of SNPs had regulatory effects. Moreover, CRISPR/Cas9-mediated deletion of this region decreased ATP2B4 transcript and protein levels and increased Ca²⁺ intracellular concentration in the K562 cell line. Our data demonstrate that severe malaria-associated genetic variants alter the expression of ATP2B4 encoding a plasma membrane calcium-transporting ATPase 4 (PMCA4) expressed on red blood cells. Altering the activity of this regulatory element affects the risk of SM, likely through calcium concentration effect on parasitaemia. Full article

Alzheimer’s disease is characterized by a marked dysregulation of intracellular Ca²⁺ homeostasis. In particular, toxic β-amyloids (Aβ) perturb the activities of numerous Ca²⁺ transporters or channels. Because of the tight coupling between Ca²⁺ dynamics and the membrane electrical activity, such perturbations are also expected to affect neuronal excitability. We used mathematical modeling to systematically investigate the effects of changing the activities of the various targets of Aβ peptides reported in the literature on calcium dynamics and neuronal excitability. We found that the evolution of Ca²⁺ concentration just below the plasma membrane is regulated by the exchanges with the extracellular medium, and is practically independent from the Ca²⁺ exchanges with the endoplasmic reticulum. Thus, disruptions of Ca²⁺ homeostasis interfering with signaling do not affect the electrical properties of the neurons at the single cell level. In contrast, the model predicts that by affecting the activities of L-type Ca²⁺ channels or Ca²⁺-activated K⁺ channels, Aβ peptides promote neuronal hyperexcitability. On the contrary, they induce hypo-excitability when acting on the plasma membrane Ca²⁺ ATPases. Finally, the presence of pores of amyloids in the plasma membrane can induce hypo- or hyperexcitability, depending on the conditions. These modeling conclusions should help with analyzing experimental observations in which Aβ peptides interfere at several levels with Ca²⁺ signaling and neuronal activity. Full article

In tumor cells with defects in apoptosis, autophagy allows prolonged survival. Autophagy leads to an accumulation of damaged mitochondria by autophagosomes. An acidic environment is maintained in compartments of cells, such as autophagosomes, late endosomes, and lysosomes; these organelles belong to the “acid store” of the cells. Nicotinic acid adenine dinucleotide phosphate (NAADP) may affect the release of Ca²⁺ from these organelles and affect the activity of Ca²⁺ ATPases and other ion transport proteins. Recently, a growing amount of evidence has shown that the variations in the expression of calcium channels or pumps are associated with the occurrence, disease-presentation, and the prognosis of colorectal cancer. We hypothesized that activity of ATPases in cancer tissue is higher because of intensive energy metabolism of tumor cells. The aim of our study was to ascertain the effect of NAADP on ATPase activity on tissue samples of colorectal cancer patients’ and healthy individuals. We tested the effect of NAADP on the activity of Na⁺/K⁺ ATPase; Ca²⁺ ATPase of endoplasmic reticulum (EPR) and plasma membrane (PM) and basal ATPase activity. Patients’ colon mucus cancer samples were obtained during endoscopy from cancer and healthy areas (control) of colorectal mucosa of the same patients. Results. The mean activity of Na⁺/K⁺ pump in samples of colorectal cancer patients (n = 5) was 4.66 ± 1.20 μmol P_i/mg of protein per hour, while in control samples from healthy tissues of the same patient (n = 5) this value was 3.88 ± 2.03 μmol P_i/mg of protein per hour. The activity of Ca²⁺ ATPase PM in control samples was 6.42 ± 0.63 μmol P_i/mg of protein per hour and in cancer −8.50 ± 1.40 μmol Pi/mg of protein per hour (n = 5 pts). The mean activity of Ca²⁺ ATPase of EPR in control samples was 7.59 ± 1.21 μmol P_i/mg versus 7.76 ± 0.24 μmol Pi/mg in cancer (n = 5 pts). Basal ATPase activity was 3.19 ± 0.87 in control samples versus 4.79 ± 1.86 μmol Pi/mg in cancer (n = 5 pts). In cancer samples, NAADP reduced the activity of Na⁺/K⁺ ATPase by 9-times (p < 0.01) and the activity of Ca²⁺ ATPase EPR about 2-times (p < 0.05). NAADP caused a tendency to decrease the activity of Ca²⁺ ATPase of PM, but increased basal ATPase activity by 2-fold vs. the mean of this index in cancer samples without the addition of NAADP. In control samples NAADP caused only a tendency to decrease the activities of Na⁺/K⁺ ATPase and Ca²⁺ ATPase EPR, but statistically decreased the activity of Ca²⁺ ATPase of PM (p < 0.05). In addition, NAADP caused a strong increase in basal ATPase activity in control samples (p < 0.01). Conclusions: We found that the activity of Na⁺/K⁺ pump, Ca²⁺ ATPase of PM and basal ATPase activity in cancer tissues had a strong tendency to be higher than in the controls. NAADP caused a decrease in the activities of Na⁺/K⁺ ATPase and Ca²⁺ ATPase EPR in cancer samples and increased basal ATPase activity. In control samples, NAADP decreased Ca²⁺ ATPase of PM and increased basal ATPase activity. These data confirmed different roles of NAADP-sensitive “acidic store” (autophagosomes, late endosomes, and lysosomes) in control and cancer tissue, which hypothetically may be connected with autophagy role in cancer development. The effect of NAADP on decreasing the activity of Na⁺/K⁺ pump in cancer samples was the most pronounced, both numerically and statistically. Our data shows promising possibilities for the modulation of ion-transport through the membrane of cancer cells by influence on the “acidic store” (autophagosomes, late endosomes and lysosomes) as a new approach to the treatment of colorectal cancer. Full article

Intracellular Ca²⁺ signaling engendered by Ca²⁺ influx and mobilization in odontoblasts is critical for dentinogenesis induced by multiple stimuli at the dentin surface. Increased Ca²⁺ is exported by the Na⁺–Ca²⁺ exchanger (NCX) and plasma membrane Ca²⁺–ATPase (PMCA) to maintain Ca²⁺ homeostasis. We previously demonstrated a functional coupling between Ca²⁺ extrusion by NCX and its influx through transient receptor potential channels in odontoblasts. Although the presence of PMCA in odontoblasts has been previously described, steady-state levels of mRNA-encoding PMCA subtypes, pharmacological properties, and other cellular functions remain unclear. Thus, we investigated PMCA mRNA levels and their contribution to mineralization under physiological conditions. We also examined the role of PMCA in the Ca²⁺ extrusion pathway during hypotonic and alkaline stimulation-induced increases in intracellular free Ca²⁺ concentration ([Ca²⁺]_i). We performed RT-PCR and mineralization assays in human odontoblasts. [Ca²⁺]_i was measured using fura-2 fluorescence measurements in odontoblasts isolated from newborn Wistar rat incisor teeth and human odontoblasts. We detected mRNA encoding PMCA1–4 in human odontoblasts. The application of hypotonic or alkaline solutions transiently increased [Ca²⁺]_i in odontoblasts in both rat and human odontoblasts. The Ca²⁺ extrusion efficiency during the hypotonic or alkaline solution-induced [Ca²⁺]_i increase was decreased by PMCA inhibitors in both cell types. Alizarin red and von Kossa staining showed that PMCA inhibition suppressed mineralization. In addition, alkaline stimulation (not hypotonic stimulation) to human odontoblasts upregulated the mRNA levels of dentin matrix protein-1 (DMP-1) and dentin sialophosphoprotein (DSPP). The PMCA inhibitor did not affect DMP-1 or DSPP mRNA levels at pH 7.4–8.8 and under isotonic and hypotonic conditions, respectively. We also observed PMCA1 immunoreactivity using immunofluorescence analysis. These findings indicate that PMCA participates in maintaining [Ca²⁺]_i homeostasis in odontoblasts by Ca²⁺ extrusion following [Ca²⁺]_i elevation. In addition, PMCA participates in dentinogenesis by transporting Ca²⁺ to the mineralizing front (which is independent of non-collagenous dentin matrix protein secretion) under physiological and pathological conditions following mechanical stimulation by hydrodynamic force inside dentinal tubules, or direct alkaline stimulation by the application of high-pH dental materials. Full article

Calcium in mammalian neurons is essential for developmental processes, neurotransmitter release, apoptosis, and signal transduction. Incorrectly processed Ca²⁺ signal is well-known to trigger a cascade of events leading to altered response to variety of stimuli and persistent accumulation of pathological changes at the molecular level. To counterbalance potentially detrimental consequences of Ca²⁺, neurons are equipped with sophisticated mechanisms that function to keep its concentration in a tightly regulated range. Calcium pumps belonging to the P-type family of ATPases: plasma membrane Ca²⁺-ATPase (PMCA), sarco/endoplasmic Ca²⁺-ATPase (SERCA) and secretory pathway Ca²⁺-ATPase (SPCA) are considered efficient line of defense against abnormal Ca²⁺ rises. However, their role is not limited only to Ca²⁺ transport, as they present tissue-specific functionality and unique sensitive to the regulation by the main calcium signal decoding protein—calmodulin (CaM). Based on the available literature, in this review we analyze the contribution of these three types of Ca²⁺-ATPases to neuropathology, with a special emphasis on mental diseases. Full article

Calcium levels have a huge impact on the physiology of the female reproductive system, in particular, of the ovaries. Cytosolic calcium levels are influenced by regulatory proteins (i.e., ion channels and pumps) localized in the plasmalemma and/or in the endomembranes of membrane-bound organelles. Imbalances between plasma membrane and organelle-based mechanisms for calcium regulation in different ovarian cell subtypes are contributing to ovarian pathologies, including ovarian cancer. In this review, we focused our attention on altered calcium transport and its role as a contributor to tumor progression in ovarian cancer. The most important proteins described as contributing to ovarian cancer progression are inositol trisphosphate receptors, ryanodine receptors, transient receptor potential channels, calcium ATPases, hormone receptors, G-protein-coupled receptors, and/or mitochondrial calcium uniporters. The involvement of mitochondrial and/or endoplasmic reticulum calcium imbalance in the development of resistance to chemotherapeutic drugs in ovarian cancer is also discussed, since Ca²⁺ channels and/or pumps are nowadays regarded as potential therapeutic targets and are even correlated with prognosis. Full article

Cytosolic calcium (Ca²⁺) transients control key neural processes, including neurogenesis, migration, the polarization and growth of neurons, and the establishment and maintenance of synaptic connections. They are thus involved in the development and formation of the neural system. In this study, a publicly available whole transcriptome sequencing (RNA-Seq) dataset was used to examine the expression of genes coding for putative plasma membrane and organellar Ca²⁺-transporting proteins (channels, pumps, exchangers, and transporters) during the formation of the cerebral cortex in mice. Four ages were considered: embryonic days 11 (E11), 13 (E13), and 17 (E17), and post-natal day 1 (PN1). This transcriptomic profiling was also combined with live-cell Ca²⁺ imaging recordings to assess the presence of functional Ca²⁺ transport systems in E13 neurons. The most important Ca²⁺ routes of the cortical wall at the onset of corticogenesis (E11–E13) were TACAN, GluK5, nAChR β2, Cav3.1, Orai3, transient receptor potential cation channel subfamily M member 7 (TRPM7) non-mitochondrial Na⁺/Ca²⁺ exchanger 2 (NCX2), and the connexins CX43/CX45/CX37. Hence, transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1), transmembrane protein 165 (TMEM165), and Ca²⁺ “leak” channels are prominent intracellular Ca²⁺ pathways. The Ca²⁺ pumps sarco/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) and plasma membrane Ca²⁺ ATPase 1 (PMCA1) control the resting basal Ca²⁺ levels. At the end of neurogenesis (E17 and onward), a more numerous and diverse population of Ca²⁺ uptake systems was observed. In addition to the actors listed above, prominent Ca²⁺-conducting systems of the cortical wall emerged, including acid-sensing ion channel 1 (ASIC1), Orai2, P2X2, and GluN1. Altogether, this study provides a detailed view of the pattern of expression of the main actors participating in the import, export, and release of Ca²⁺. This work can serve as a framework for further functional and mechanistic studies on Ca²⁺ signaling during cerebral cortex formation. Full article

Background: The LA hybrid lily ‘Aladdin’ has both excellent traits of Longiflorum hybrids and Asiatic hybrids—such as big and vivid flower, strong stem, high self-propagation coefficient, and shorter low temperature time required to release bulb dormancy in contrast to Oriental hybrids. A genome-wide transcriptional analysis using transcriptome RNA-Seq was performed in order to explore whether there is a gibberellin floral induction pathway in the LA hybrid lily. Subsequently, gene co-expression network analysis was used to analyze the possible interactions of key candidate genes screened from transcriptome data. At the same time, a series of physiological, biochemical, and cultivation tests were carried out. Results: The content of five endogenous hormones changed sharply in the shoot apex during the treatment of 200 mg/L exogenous gibberellin and the ratio of ABA/GA₃ dropped and stayed at a lower level after 4 hours’ treatment from the higher levels initially, reaching a dynamic balance. In addition, the metabolism of carbohydrates in the bulbs increase during exogenous gibberellin treatment. A total of 124,041 unigenes were obtained by RNA-seq. With the transcriptome analysis, 48,927 unigenes and 48,725 unigenes respectively aligned to the NR database and the Uniprot database. 114,138 unigenes, 25,369 unigenes, and 19,704 unigenes respectively aligned to the COG, GO, and KEGG databases. 2148 differentially expression genes (DEGs) were selected with the indicators RPKM ≥ 0, FDR ≤ 0.05 and |log2(ratio)| ≥ 2. The number of the upregulated unigenes was significantly more than the number of the downregulated unigenes. Some MADS-box genes related to flowering transformation—such as AGL20, SOC1, and CO—were found to be upregulated. A large number of gibberellin biosynthesis related genes such as GA2ox, GA3ox, GA20ox, Cytochrome P450, CYP81, and gibberellin signal transduction genes such as DELLA, GASA, and GID1 were significantly differentially expressed. The plant hormones related genes such as NCED3 and sugar metabolism related genes such as α-amylase, sucrose synthase hexokinase, and so on were also found expressing differentially. In addition, stress resistance related genes such as LEA1, LEA2, LEA4, serine/threonine protein kinase, LRR receptor-like serine/threonine protein kinase, P34 kinase, histidine kinase 3 and epigenetic related genes in DNA methylation, histone methylation, acetylation, ubiquitination of ribose were also found. Particularly, a large number of transcription factors responsive to the exogenous gibberellin signal including WRKY40, WRKY33, WRKY27, WRKY21, WRKY7, MYB, AP2/EREBP, bHLH, NAC1, NAC2, and NAC11 were found to be specially expressing. 30 gene sequences were selected from a large number of differentially expressed candidate genes for qRT-PCR expression verification (0, 2, 4, 8, and 16 h) and compared with the transcriptome expression levels. Conclusions: 200mg/L exogenous GA₃ can successfully break the bulb’s dormancy of the LA hybrid lily and significantly accelerated the flowering process, indicating that gibberellin floral induction pathway is present in the LA lily ‘Aladdin’. With the GCNs analysis, two second messenger G protein-coupled receptor related genes that respond to gibberellin signals in the cell were discovered. The downstream transport proteins such as AMT, calcium transport ATPase, and plasma membrane ATPase were also discovered participating in GA signal transduction. Transcription factors including WRKY7, NAC2, NAC11, and CBF specially regulated phosphorylation and glycosylation during the ubiquitination degradation process of DELLA proteins. These transcription factors also activated in abscisic acid metabolism. A large number of transcription factors such as WRKY21, WRKY22, NAC1, AP2, EREB1, P450, and CYP81 that both regulate gibberellin signaling and low-temperature signals have also been found. Finally, the molecular mechanism of GA floral induction pathway in the LA hybrid lily ‘Aladdin’ was constructed. Full article

Boron (B) is a micronutrient for plant development, and its deficiency alters many physiological processes. However, the current knowledge on how plants are able to sense the B-starvation signal is still very limited. Recently, it has been reported that B deprivation induces an increase in cytosolic calcium concentration ([Ca²⁺]_cyt) in Arabidopsis thaliana roots. The aim of this work was to research in Arabidopsis whether [Ca²⁺]_cyt is restored to initial levels when B is resupplied and elucidate whether apoplastic Ca²⁺ is the major source for B-deficiency-induced rise in [Ca²⁺]_cyt. The use of chemical compounds affecting Ca²⁺ homeostasis showed that the rise in root [Ca²⁺]_cyt induced by B deficiency was predominantly owed to Ca²⁺ influx from the apoplast through plasma membrane Ca²⁺ channels in an IP₃-independent manner. Furthermore, B resupply restored the root [Ca²⁺]_cyt. Interestingly, expression levels of genes encoding Ca²⁺ transporters (ACA10, plasma membrane P_IIB-type Ca²⁺-ATPase; and CAX3, vacuolar cation/proton exchanger) were upregulated by ethylene glycol tetraacetic acid (EGTA) and abscisic acid (ABA). The results pointed out that ACA10, and especially CAX3, would play a major role in the restoration of Ca²⁺ homeostasis after 24 h of B deficiency. Full article

Zebrafish is an emerging model for the research of body fluid ionic homeostasis. In this review, we focus on current progress on the regulation of Ca²⁺ uptake in the context of Ca²⁺ sensing and hormonal regulation in zebrafish. Na⁺-K⁺-ATPase-rich cells (NaRCs), the specialized ionocytes in the embryonic skin and adult gills, play a dominant role in Ca²⁺ uptake in zebrafish. Transepithelial Ca²⁺ transport in NaRC, through apical epithelial Ca²⁺ channels (ECaC), basolateral plasma membrane Ca²⁺-ATPase (PMCA), and Na⁺/Ca²⁺ exchanger (NCX), is analogous to mammalian renal and intestinal Ca²⁺-absorption cells. Several hormones were demonstrated to differentially regulate Ca²⁺ uptake through modulating the expression of Ca²⁺ transporters and/or the proliferation/differentiation of NaRC in zebrafish. In addition, the counterbalance among these hormones is associated with the maintenance of body fluid Ca²⁺ homeostasis. Calcium-sensing receptor (CaSR) is expressed in several hormone-secreting tissues in zebrafish, and activated CaSR differentially controls calciotropic hormones. The major principles of Ca²⁺ transport and the hormonal control appear to be conserved from zebrafish to other vertebrates including mammals. The new knowledge gained from zebrafish studies provides new insights into the related issues in vertebrates. Full article

Octylphenol (OP) and bisphenol A (BPA) are known as endocrine-disrupting chemicals (EDCs). During pregnancy, the expression of steroid hormone receptors is controlled by maternal and fetal nutrition. To evaluate the impact of EDCs during pregnancy, ethinyl estradiol (EE, 0.2 mg/kg/day), OP (50 mg/kg/day), and BPA (50 mg/kg/day) were administered to pregnant mice. The mRNA levels of TRPV6 (transient receptor potential cation channels in subfamily V, member 6) decreased significantly by EE and OP. The PMCA1 (ATPase, Ca⁺⁺ transporting, plasma membrane 1) mRNA and protein levels decreased significantly by EE, OP, and BPA. CTR1 (solute carrier family 31, member 1) and ATP7A (ATPase, Cu⁺⁺ transporting, alpha polypeptide) expression decreased significantly by EE, OP, and BPA. The mRNA levels of IREG1 (iron-regulated transporter, member 1) decreased significantly by EE. Hephaestin (HEPH) mRNA levels decreased significantly by EE, OP, and BPA, and protein levels decreased significantly by BPA. As a result of immunohistochemistry analysis, all cation transporter proteins were found in labyrinth of placenta. To confirm the cytosolic level of cations, levels of cation level in fetal serum were measured. EE, OP, and BPA significantly reduced serum calcium and copper levels, and iron levels were reduced by BPA. Taken together, some EDCs, such as OP and BPA, could modulate the calcium, copper, and iron ion-transporting channels during pregnancy. The fetus relies on the mother for ionic transportation, and, therefore, pregnant women should avoid exposure to cation-channel-disrupting chemicals. Full article

Stanniocalcin-1 (STC1) is a calcium and phosphate regulatory hormone. However, the exact molecular mechanisms underlying how STC1 affects Ca²⁺ uptake remain unclear. Here, the expression levels of the calcium transport proteins involved in transcellular transport in Caco2 cells were examined following over-expression or inhibition of STC1. These proteins include the transient receptor potential vanilloid members (TRPV) 5 and 6, the plasma membrane calcium ATPase 1b (PMCA1b), the sodium/calcium exchanger (NCX1), and the vitamin D receptor (VDR). Both gene and protein expressions of TRPV5 and TRPV6 were attenuated in response to over-expression of STC1, and the opposite trend was observed in cells treated with siRNA_STC1. To further investigate the ability of STC1 to influence TRPV6 expression, cells were treated with 100 ng/mL of recombinant human STC1 (rhSTC1) for 4 h following pre-transfection with siRNA_STC1 for 48 h. Intriguingly, the increase in the expression of TRPV6 resulting from siRNA_STC1 was reversed by rhSTC1. No significant effect of STC1 on the expression of PMCA1b, NCX1 or VDR was observed in this study. In conclusion, the effect of STC1 on calcium transport in intestinal epithelia is due to, at least in part, its negative regulation of the epithelial channels TRPV5/6 that mediate calcium influx. Full article