A therapeutic strategy to target distinct sources of IgE and durably reverse allergy.

Immunoglobulin E (IgE) is a key driver of type 1 hypersensitivity reactions and allergic disorders, which are globally increasing in number and severity. Although eliminating pathogenic IgE may be a powerful way to treat allergy, no therapeutic strategy reported to date can fully ablate IgE production. Interleukin-4 receptor α (IL-4Rα) signaling is required for IgE class switching, and IL-4Rα blockade gradually reduces, but does not eliminate, IgE. The persistence of IgE after IL-4Rα blockade may be due to long-lived IgE+ plasma cells that maintain serological memory to allergens and thus may be susceptible to plasma cell-targeted therapeutics. We demonstrate that transient administration of a B cell maturation antigen x CD3 (BCMAxCD3) bispecific antibody markedly depletes IgE, as well as other immunoglobulins, by ablating long-lived plasma cells, although IgE and other immunoglobulins rapidly rebound after treatment. Concomitant IL-4Rα blockade specifically and durably prevents the reemergence of IgE by blocking IgE class switching while allowing the restoration of other immunoglobulins. Moreover, this combination treatment prevented anaphylaxis in mice. Together with additional cynomolgus monkey and human data, our studies demonstrate that allergic memory is primarily maintained by both non-IgE+ memory B cells that require class switching and long-lived IgE+ plasma cells. Our combination approach to durably eliminate pathogenic IgE has potential to benefit allergy in humans while preserving antibody-mediated immunity.

Stem cell exosomes inhibit angiogenesis and tumor growth of oral squamous cell carcinoma.

Recently, exosomes secreted by menstrual mesenchymal stem cells have been identified as inhibitory agents of tumor angiogenesis and modulators of the tumor cell secretome in prostate and breast cancer. However, their direct effect on endothelial cells and paracrine mediators have not yet been investigated. Using a carrier-based cell culture system to test the scalability for exosome production, we showed that different types of endothelial cells present specific kinetics for exosomes internalization. Exosome-treatment of endothelial cells increased cytotoxicity and reduced VEGF secretion and angiogenesis in a dose-dependent manner. Using the hamster buccal pouch carcinoma as a preclinical model for human oral squamous cell carcinoma, we demonstrated a significant antitumor effect of intra-tumoral injection of exosomes associated with a loss of tumor vasculature. These results address up-scaling of exosome production, a relevant issue for their clinical application, and also assess menstrual stem cell exosomes as potential anti-angiogenic agents for the treatment of neoplastic conditions.

Differential regulation of TNF receptors in maternal leukocytes is associated with severe preterm preeclampsia.

We tested the hypothesis that maternal peripheral blood leukocytes contribute to elevated levels of soluble TNF receptors (sTNFR) in preeclampsia (PE) with concomitant intrauterine growth restriction (IUGR). TNFR1 and TNFR2 were evaluated in a cross-sectional study comparing preeclamptic (n = 15) with or without IUGR versus normotensive pregnant women (PREG, n = 30), and non-pregnant controls (Con; n = 20). Plasma levels of sTNFR1 were higher in PE (1675.0 ± 227.1 pg/mL) compared with PREG (1035.0 ± 101.1 pg/mL) and Con (589.3 ± 82.67 pg/mL), with the highest values observed in PE with IUGR (2624.0 ± 421.4 pg/mL; n = 6). Plasma sTNFR2 was higher during pregnancy (PE: 1836.0 ± 198.7 pg/mL; PREG: 1697.0 ± 95.0 pg/mL) compared with Con (598.3 ± 82.7 pg/mL). Urinary levels of sTNFR1 and sTNFR2 were higher in PE and PREG compared with the Con group. Abundance of TNFR1 mRNA in peripheral blood leukocytes was strongly correlated with plasma levels of sTNFR1 in PE. However, TNFR2 mRNA accumulation in leukocytes did not correlate with sTNFR2 plasma levels. The level of sTNFR1 in plasma was correlated with body weight of the newborn (r = -0.56). The data suggest that maternal leukocytes contribute to sTNFR1 levels in plasma in association with decreasing newborn weight and PE with concomitant IUGR.

Tumor necrosis factor-alpha induces renal cyclooxygenase-2 expression in response to hypercalcemia.

The effect of tumor necrosis factor-alpha (TNF) on cyclooxygenase-2 (COX-2) expression in the renal outer medulla (OM) was determined in a model of dihydrotachysterol (DHT)-induced hypercalcemia. Increases in serum calcium and water intake were observed during ingestion of a DHT-containing diet in both wild type (WT) and TNF deficient mice (TNF(-/-)). Polyuria and a decrease in body weight were observed in response to DHT treatment in WT and TNF(-/-) mice. A transient elevation in urinary TNF was observed in WT mice treated with DHT. Moreover, increased urinary levels of prostaglandin E(2) (PGE(2)) and a corresponding increase in COX-2 expression in the OM were observed in WT mice fed DHT. Increased COX-2 expression was not observed in TNF(-/-) mice fed DHT, and the characteristics of PGE(2) synthesis were distinct from those in WT mice. This study demonstrates that COX-2 expression in the OM, secondary to hypercalemia, is TNF-dependent.

Eicosanoids and tumor necrosis factor-alpha in the kidney.

The thick ascending limb of Henle's loop (TAL) is capable of metabolizing arachidonic acid (AA) by cytochrome P450 (CYP450) and cyclooxygenase (COX) pathways and has been identified as a nephron segment that contributes to salt-sensitive hypertension. Previous studies demonstrated a prominent role for CYP450-dependent metabolism of AA to products that inhibited ion transport pathways in the TAL. However, COX-2 is constitutively expressed along all segments of the TAL and is increased in response to diverse stimuli. The ability of Tamm-Horsfall glycoprotein, a selective marker of cortical TAL (cTAL) and medullary (mTAL), to bind TNF and localize it to this nephron segment prompted studies to determine the capacity of mTAL cells to produce TNF and determine its effects on mTAL function. The colocalization of calcium-sensing receptor (CaR) and COX-2 in the TAL supports the notion that activation of CaR induces TNF-dependent COX-2 expression and PGE2 synthesis in mTAL cells. Additional studies showed that TNF produced by mTAL cells inhibits 86Rb uptake, an in vitro correlate of natriuresis, in an autocrine- and COX-2-dependent manner. The molecular mechanism for these effects likely includes inhibition of Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2) expression and trafficking.

Tumor necrosis factor-alpha is an endogenous inhibitor of Na+-K+-2Cl- cotransporter (NKCC2) isoform A in the thick ascending limb.

The effects of TNF gene deletion on renal Na(+)-K(+)-2Cl(-) cotransporter (NKCC2) expression and activity were determined. Outer medulla from TNF(-/-) mice exhibited a twofold increase in total NKCC2 protein expression compared with wild-type (WT) mice. This increase was not observed in TNF(-/-) mice treated with recombinant human TNF (hTNF) for 7 days. Administration of hTNF had no effect on total NKCC2 expression in WT mice. A fourfold increase in NKCC2A mRNA accumulation was observed in outer medulla from TNF(-/-) compared with WT mice; NKCC2F and NKCC2B mRNA accumulation was similar between genotypes. The increase in NKCC2A mRNA accumulation was attenuated when TNF(-/-) mice were treated with hTNF. Bumetanide-sensitive O(2) consumption, an in vitro correlate of NKCC2 activity, was 2.8 ± 0.2 nmol·min(-1)·mg(-1) in medullary thick ascending limb tubules from WT, representing ∼40% of total O(2) consumption, whereas, in medullary thick ascending limb tubules from TNF(-/-) mice, it was 5.6 ± 0.3 nmol·min(-1)·mg(-1), representing ∼60% of total O(2) consumption. Administration of hTNF to TNF(-/-) mice restored the bumetanide-sensitive component to ∼30% of total O(2) consumption. Ambient urine osmolality was higher in TNF(-/-) compared with WT mice (2,072 ± 104 vs. 1,696 ± 153 mosmol/kgH(2)O, P < 0.05). The diluting ability of the kidney, assessed by measuring urine osmolality before and after 1 h of water loading also was greater in TNF(-/-) compared with WT mice (174 ± 38 and 465 ± 81 mosmol/kgH(2)O, respectively, P < 0.01). Collectively, these findings suggest that TNF plays a role as an endogenous inhibitor of NKCC2 expression and function.

TNFR1-deficient mice display altered blood pressure and renal responses to ANG II infusion.

The hypothesis that TNF receptor 1-deficient (TNFR1(-/-)) mice display blood pressure (BP) and renal functional responses that differ from wild-type (WT) mice was tested in an angiotensin II (ANG II)-dependent model of hypertension. Basal systolic BP (SBP), mean arterial pressure, diastolic BP, heart rate (HR), and pulse pressure were similar in WT and TNFR1(-/-) mice. Infusion of ANG II for 7 days elevated SBP to a greater extent in TNFR1(-/-) compared with WT mice; pulse pressure was also elevated in TNFR1(-/-). HR decreased in TNFR1(-/-) mice infused with ANG II, an effect prominent on day 1. Basal urinary albumin excretion was similar in WT and TNFR1(-/-) mice but was higher in TNFR1(-/-) in response to ANG II infusion. Water intake and urine volume were increased by ANG II infusion; this increase was higher in TNFR1(-/-) vs. WT mice, whereas body weight and food intake were unaffected. Baseline creatinine clearance (Ccr), urinary sodium excretion, and fractional excretion of sodium (FE(Na)%) were similar in vehicle-treated WT and TNFR1(-/-) mice. ANG II infusion for 7 days increased Ccr and filtered load of sodium in TNFR1(-/-) but not WT mice, whereas it elicited an increase in FE(Na)% and urinary sodium excretion in WT but not TNFR1(-/-) mice. ANG II also inhibited renal TNFR1 mRNA accumulation while increasing that of TNFR2. These findings indicate deletion of TNFR1 is associated with an exacerbated SBP response, decrease in HR, and altered renal function in ANG II-dependent hypertension.

Calcium-sensing receptor signaling pathways in medullary thick ascending limb cells mediate COX-2-derived PGE2 production: functional significance.

We determined the functional implications of calcium-sensing receptor (CaR)-dependent, Gq- and Gi-coupled signaling cascades, which work in a coordinated manner to regulate activity of nuclear factor of activated T cells and tumor necrosis factor (TNF)-alpha gene transcription that cause expression of cyclooxygenase (COX)-2-derived prostaglandin E2 (PGE2) synthesis by rat medullary thick ascending limb cells (mTAL). Interruption of Gq, Gi, protein kinase C (PKC), or calcineurin (CaN) activities abolished CaR-mediated COX-2 expression and PGE2 synthesis. We tested the hypothesis that these pathways contribute to the effects of CaR activation on ion transport in mTAL cells. Ouabain-sensitive O2 consumption, an in vitro correlate of ion transport in the mTAL, was inhibited by approximately 70% in cells treated for 6 h with extracellular Ca2+ (1.2 mM), an effect prevented in mTAL cells transiently transfected with a dominant negative CaR overexpression construct (R796W), indicating that the effect was initiated by stimulation of the CaR. Pretreatment with the COX-2-selective inhibitor, NS-398 (1 microM), reversed CaR-activated decreases in ouabain-sensitive O2 consumption by approximately 60%, but did not alter basal levels of ouabain-sensitive O2 consumption. Similarly, inhibition of either Gq, Gi, PKC, or CaN, which are components of the mechanism associated with CaR-stimulated COX-2-derived PGE2 synthesis, reversed the inhibitory effects of CaR on O2 consumption without affecting basal O2 consumption. Our findings identified signaling elements required for CaR-mediated TNF production that are integral components regulating mTAL function via a mechanism involving COX-2 expression and PGE2 production.

CaR activation increases TNF production by mTAL cells via a Gi-dependent mechanism.

We evaluated the contribution of calcium-sensing receptor (CaR)-mediated G(i)-coupled signaling to TNF production in medullary thick ascending limb (mTAL) cells. A selective G(i) inhibitor, pertussis toxin (PTX), but not the inactive B-oligomer binding subunit, abolished CaR-mediated increases in TNF production. The inhibitory effect of PTX was partially reversed by using an adenylate cyclase inhibitor. CaR-mediated TNF production also was partially reversed by a cAMP analog, 8-Br-cAMP. IP(1) accumulation was CaR dependent and blocked by PI-PLC; partial inhibition also was observed with PTX. CaR increased calcineurin (CaN) activity by approximately threefold, and PTX prevented CaR-mediated increases in CaN activity, an nuclear factor of activated T cells (NFAT)-cis reporter construct, and a TNF promoter construct. The interaction between G(i) and PKC was determined, as we previously showed that CaR-mediated TNF production was CaN and NFAT- mediated and G(q) dependent. CaR activation increased PKC activity by twofold, an effect abolished by transient transfection with a dominant negative CaR construct, R796W, or pretreatment with PTX. Inhibition with the pan-specific PKC inhibitor GF 109203X (20 nM) abolished CaR-mediated increases in activity of CaN, an NFAT reporter, and a TNF promoter construct. Collectively, the data suggest that G(i)-coupled signaling contributes to NFAT-mediated TNF production in a CaN- and PKC-dependent manner and may be part of a CaR mechanism to regulate mTAL function. Moreover, concurrent G(q) and G(i) signaling is required for CaR-mediated TNF production in mTAL cells via a CaN/NFAT pathway that is PKC dependent. Understanding CaR-mediated signaling pathways that regulate TNF production in the mTAL is crucial to defining novel mechanisms that regulate extracellular fluid volume and salt balance.

Characterization of a long-term rat mTAL cell line.

A medullary thick ascending limb (mTAL) cell line, termed raTAL, has been established from freshly isolated rat mTAL tubules and cultured continuously for up to 75 passages; it retains characteristics of mTAL cells even after retrieval from storage in liquid nitrogen for several months. The cells express Tamm-Horsfall glycoprotein (THP), a TAL-specific marker, grow to confluence, exhibit a polygonal morphology characteristic of epithelial cells, and form "domes." Detection of THP, Na(+)-K(+)-2Cl(-) cotransporter (NKCC2), Na(+)-K(+)-ATPase, and renal outer medullary K(+) channel (ROMK) was achieved using indirect immunofluorescence and confocal microscopy. Western blot analysis of NKCC2 expression using two different antibodies revealed a band of approximately 160 kDa, and RT-PCR analysis demonstrated the presence of NKCC2 isoforms A and F, which was confirmed by DNA sequencing; transport of Cl(-) into raTAL cells was inhibited by furosemide. Ouabain- and bumetanide-sensitive oxygen consumption, an index of ion transport activity in the mTAL, was observed in raTAL cells, and the number of domes present was reduced significantly when cells were incubated in the presence of ouabain or bumetanide. The specific activity of Na(+)-K(+)-ATPase activity was determined in raTAL cells (0.67 +/- 0.18 nmol P(i).microg protein(-1).min(-1)), primary cultures of mTAL cells (0.39 +/- 0.08 nmol P(i).microg protein(-1).min(-1)), and freshly isolated mTAL tubules (1.10 +/- 0.29 nmol P(i).microg protein(-1).min(-1)), and approximately 30-50% of total cellular ATPase activity was inhibited by ouabain, in accord with other mTAL preparations. This cell line will be used in studies that address biochemical, molecular, and physiological mechanisms in the mTAL.

NFAT regulates calcium-sensing receptor-mediated TNF production.

Because nuclear factor of activated T cells (NFAT) has been implicated in TNF production as well as osmoregulation and salt and water homeostasis, we addressed whether calcium-sensing receptor (CaR)-mediated TNF production in medullary thick ascending limb (mTAL) cells was NFAT dependent. TNF production in response to addition of extracellular Ca(2+) (1.2 mM) was abolished in mTAL cells transiently transfected with a dominant-negative CaR construct (R796W) or pretreated with the phosphatidylinositol phospholipase C (PI-PLC) inhibitor U-73122. Cyclosporine A (CsA), an inhibitor of the serine/threonine phosphatase calcineurin, and a peptide ligand, VIVIT, that selectively inhibits calcineurin-NFAT signaling, also prevented CaR-mediated TNF production. Increases in calcineurin activity in cells challenged with Ca(2+) were inhibited after pretreatment with U-73122 and CsA, suggesting that CaR activation increases calcineurin activity in a PI-PLC-dependent manner. Moreover, U-73122, CsA, and VIVIT inhibited CaR-dependent activity of an NFAT construct that drives expression of firefly luciferase in transiently transfected mTAL cells. Collectively, these data verify the role of calcineurin and NFAT in CaR-mediated TNF production by mTAL cells. Activation of the CaR also increased the binding of NFAT to a consensus oligonucleotide, an effect that was blocked by U-73122 and CsA, suggesting that a calcineurin- and NFAT-dependent pathway increases TNF production in mTAL cells. This mechanism likely regulates TNF gene transcription as U-73122, CsA, and VIVIT blocked CaR-dependent activity of a TNF promoter construct. Elucidating CaR-mediated signaling pathways that regulate TNF production in the mTAL will be crucial to understanding mechanisms that regulate extracellular fluid volume and salt balance.

Exaggerated response to adenosine in kidneys from high salt-fed rats: role of epoxyeicosatrienoic acids.

Cytochrome P-450 (CYP)-dependent epoxyeicosatrienoic acids (EETs) dilate rat preglomerular microvessels when adenosine(2A) receptors (A(2A)R) are stimulated. As high salt (HS) intake increases epoxygenase activity and adenosine levels, we hypothesized that renal adenosine responses would be greater in HS-fed rats. Male Sprague-Dawley rats were fed either HS (4.0% NaCl) or normal salt (NS; 0.4% NaCl) diet. On day 8, isolated kidneys were perfused with Krebs' buffer containing indomethacin (10 microM) and L-NAME (200 microM) and preconstricted to approximately 150 mmHg with infusion of phenylephrine (10(-7) M). Renal effluents were extracted for analysis of eicosanoids by gas chromatography-mass spectrometry. Bolus injections of the stable adenosine analog 2-chloroadenosine (2-CA; 0.1-10 microg) resulted in dose-dependent dilation; at 10 microg, perfusion pressure (PP) was lowered to a greater extent in the kidneys of HS rats compared with NS rats (-60 +/- 4 vs. -31 +/- 8 mmHg; P < 0.05) and the area of response was increased (27 +/- 6 vs. 9 +/- 4 mm(2); P < 0.05), as was EET release (132 +/- 23 vs. 38 +/- 18 ng; P < 0.05). HS treatment increased A(2A)R and CYP2C23 protein expression. A selective epoxygenase inhibitor, MS-PPOH (12 microM), significantly reduced the response to 2-CA in HS rats; PP, area of response, and EET release decreased by 40, 70, and 81%, respectively, whereas lesser changes were evident in NS kidneys. Thus the greater vasodilator response to 2-CA seen in kidneys obtained from HS-fed rats was mediated by increased EET release. As EETs are renal vasodilator and natriuretic eicosanoids, interactions between adenosine and EETs may contribute to the adaptive response to HS intake.

Bradykinin regulates cyclooxygenase-2 in rat renal thick ascending limb cells.

Cyclooxygenase-2 (COX-2) is constitutively expressed in a subset of thick ascending limb cells in the cortex and medulla and increases when the renin-angiotensin and kallikrein-kinin systems are activated. Although the contribution of angiotensin II to the regulation of COX-2 is known, the effects of bradykinin on COX-2 expression have not been determined in this nephron segment. We evaluated expression of B2 bradykinin receptors in thick ascending limb cells containing COX-2 and the effect of bradykinin on COX-2 expression in primary cultured medullary thick ascending cells. The presence of B2 receptors was studied in renal sections by immunohistochemistry with antibodies against B2, COX-2, and Tamm-Horsfall glycoprotein. B2 receptors were detected on the apical and basolateral portion of the thick ascending cells. These cells also contained COX-2, suggesting that COX-2 expression may be regulated via B2 receptor. Incubation of cultured medullary thick ascending cells with bradykinin (10(-7) to 10(-5) mol/L) induced a significant increase on COX-2 protein expression. Maximal expression of COX-2 was observed 4 hours after exposure to bradykinin (10(-7) mol/L), effect abolished by a B2 receptor antagonist (HOE-140; 10(-6) mol/L). Prostaglandin E2 production increased when these cells were challenged with bradykinin for 4 hours, indicating that COX-2 was enzymatically active. We have demonstrated (1) the presence of B2 receptors in thick ascending limb cells expressing COX-2 and (2) the stimulatory effect of bradykinin on COX-2 protein expression, via B2 receptors, in cultured medullary thick ascending cells. We suggest that bradykinin can affect ion transport in the thick ascending limb via a COX-2-mediated mechanism.

Acute application of TNF stimulates apical 70-pS K+ channels in the thick ascending limb of rat kidney.

TNF has been shown to be synthesized by the medullary thick ascending limb (mTAL) (21). In the present study, we used the patch-clamp technique to study the acute effect of TNF on the apical 70-pS K+ channel in the mTAL. Addition of TNF (10 nM) significantly stimulated activity of the 70-pS K+ channel and increased NPo [a product of channel open probability (Po) and channel number (N)] from 0.20 to 0.97. The stimulatory effect of TNF was observed only in cell-attached patches but not in excised patches. Moreover, addition of TNF had no effect on the ROMK-like small-conductance K+ channels in the TAL. The dose-response curve of the TNF effect yielded a Km value of 1 nM, a concentration that increased channel activity to 50% maximal stimulatory effect of TNF. The concentrations required for reaching the plateau of the TNF effect were between 5 and 10 nM. The stimulatory effect of TNF on the 70-pS K+ channel was observed in the presence of N(omega)-nitro-L-arginine methyl ester. This indicated that the effect of TNF was not mediated by a nitric oxide-dependent pathway. Also, inhibition of PKA did not affect the stimulatory effect of TNF. In contrast, inhibition of protein tyrosine kinase not only increased activity of the 70-pS K+ channel but also abolished the effect of TNF. Moreover, inhibition of protein tyrosine phosphatase (PTP) blocked the stimulatory effect of TNF on the 70-pS K+ channel. The notion that the TNF effect results from stimulation of PTP activity is supported by PTP activity assay in which treatment of mTAL cells with TNF significantly increased the activity of PTP. We conclude that TNF stimulates the 70-pS K+ channel via stimulation of PTP in the mTAL.

In vitro model of "wound healing" analyzed by laser scanning cytometry: accelerated healing of epithelial cell monolayers in the presence of hyaluronate.

BACKGROUND: In vitro models of "wound healing" rely on analysis of confluent cell cultures that are mechanically wounded, e.g., by scratching the cell monolayer. Damage and removal of cells during wounding provides mitogenic signals to the adjacent cells and induces their migration to close the wound. The progress of healing is generally estimated by microscopy or time-lapse cinematography by assessing cell proliferation and/or migration that leads to the wound closure. METHODS: The aim of the present study was to adapt laser scanning cytometry (LSC) to measure cellular changes related to damage and recovery of a monolayer of primary epithelial cells from rat kidneys growing with and without hyaluronate ( approximately 6 x 10(6) average molecular weight). Because x-y coordinates of the cell position on the slide were recorded by LSC, the apoptotic and proliferative changes in individual cells induced by wounding and wound closure could be correlated, by multiparameter analysis, with the cell location with respect to the wound. RESULTS: The initial change, observed as soon as 4 h after scratching and seen among the cells at the wound edge, was the appearance of apoptotic cells, characterized by cell shrinkage, typically condensed chromatin, and activation of caspases, the latter detected by binding of fluorochrome-labeled inhibitor of caspases. Their frequency was reduced to up to sixfold in the presence of hyaluronate. Cell proliferation, measured by frequency of cells incorporating bromodeoxyuridine, also reflected by percentage of cells in S, G(2), and mitosis, was higher in proximity of the wound but was not significantly affected by hyaluronate. However, the monolayer gap closure was accelerated in the presence of hyaluronate. CONCLUSIONS: By offering the means to measure apoptosis and proliferation in relation to the cell position (distance) with respect to the wound in cell monolayer and to relocate them for visual inspection, LSC is uniquely suited to quantitatively analyze in vitro the process of wound healing. Hyaluronate, the ubiquitous component of intercellular matrix, preparations of which are being used in the clinic to suppress inflammatory reactions in tissues and promote healing, accelerated the healing process by protecting cells from apoptosis and stimulating cell migration to close the gap in the cell monolayer.

Calcium-sensing receptor-mediated TNF production in medullary thick ascending limb cells.

Medullary thick ascending limb (mTAL) cells in primary culture express the Ca(2+)-sensing receptor (CaR), a G protein-coupled receptor that senses changes in extracellular Ca(2+) (Ca(o)(2+)) concentration, resulting in increases of intracellular Ca(2+) concentration and PKC activity. Exposure of mTAL cells to either Ca(o)(2+) or the CaR-selective agonist poly-L-arginine increased TNF-alpha synthesis. Moreover, the response to Ca(o)(2+) was enhanced in mTAL cells transfected with a CaR overexpression vector. Transfection of mTAL cells with a TNF promoter construct revealed an increase in reporter gene activity after exposure of the cells to Ca(o)(2+), suggesting that intracellular signaling pathways initiated by means of activation of a CaR contribute to TNF synthesis by a mechanism that involves transcription of the TNF gene. Neutralization of TNF activity with an anti-TNF antibody attenuated Ca(2+)-mediated increases in cyclooxygenase-2 (COX-2) protein expression and PGE(2) synthesis, suggesting that TNF exerts an autocrine effect in the mTAL, which contributes to COX-2-mediated PGE(2) production. Preincubation with the PKC inhibitor bisindolylmaleimide I inhibited Ca(2+)-mediated TNF production. Significant inhibition of COX-2 protein expression and PGE(2) synthesis also was observed when cells were challenged with Ca(o)(2+) in the presence of bisindolylmaleimide I. The data suggest that increases in TNF production subsequent to activation of the CaR may be the basis of an important renal mechanism that regulates salt and water excretion.