Faculty Bibliography

Cross linking of the IgE receptor (FcepsilonRI) on mast cells plays a critical role in IgE-dependent allergy including allergic rhinitis, asthma, anaphylaxis, and delayed type hypersensitivity reactions. The Ca2+ activated K+ channel, KCa3.1, plays a critical role in IgE-stimulated Ca2+ entry and degranulation in mast cells by helping to maintain a negative membrane potential, which provides an electrochemical gradient to drive Ca2+ influx. Of the 3 classes of PI3K, the class II PI3Ks are the least studied and little is known about the roles for class II PI3Ks in vivo in the context of the whole organism under normal and pathological conditions. Studying bone marrow derived mast cells (BMMC) isolated from PI3KC2beta-/- mice, we now show that the class II PI3KC2beta is critical for FcepsilonRI stimulated KCa3.1 channel activation and the subsequent activation of mast cells. We found FcepsilonRI-stimulated Ca2+ entry, cytokine production, and degranulation are decreased in BMMC isolated from PI3KC2beta-/- mice. In addition, PI3KC2beta-/- mice are markedly resistant to both passive cutaneous and passive systemic anaphylaxis. These findings identify PI3KC2beta as a new pharmacologic target to treat IgE-mediated disease.

Regulation of integrins is critical for lymphocyte adhesion to endothelium and migration throughout the body. Inside-out signaling to integrins is mediated by the small GTPase Ras-proximate-1 (Rap1). Using an RNA-mediated interference screen, we identified phospholipase Cepsilon 1 (PLCepsilon1) as a crucial regulator of stromal cell-derived factor 1 alpha (SDF-1alpha)-induced Rap1 activation. We have shown that SDF-1alpha-induced activation of Rap1 is transient in comparison with the sustained level following cross-linking of the antigen receptor. We identified that PLCepsilon1 was necessary for SDF-1alpha-induced adhesion using shear stress, cell morphology alterations, and crawling on intercellular adhesion molecule 1 (ICAM-1)-expressing cells. Structure-function experiments to separate the dual-enzymatic function of PLCepsilon1 uncover necessary contributions of the CDC25, Pleckstrin homology, and Ras-associating domains, but not phospholipase activity, to this pathway. In the mouse model of delayed type hypersensitivity, we have shown an essential role for PLCepsilon1 in T-cell migration to inflamed skin, but not for cytokine secretion and proliferation in regional lymph nodes. Our results reveal a signaling pathway where SDF-1alpha induces T-cell adhesion through activation of PLCepsilon1, suggesting that PLCepsilon1 is a specific potential target in treating conditions involving migration of T cells to inflamed organs.

BACKGROUND: -Chronic heart failure (HF) is associated with altered signal transduction via beta-adrenoceptors and G proteins, and with reduced cAMP formation. Nucleoside diphosphate kinases (NDPKs) are enriched at the plasma membrane of end-stage HF patients, but the functional consequences of this are largely unknown, particularly for NDPK-C. Here, we investigated the potential role of NDPK-C in cardiac cAMP formation and contractility. METHODS: -Real-time PCR, (Far) Western blot, immunoprecipitation, and immunocytochemistry were used to study the expression, interaction with G proteins, and localization of NDPKs. cAMP levels were determined using immunoassays or fluorescent resonance energy transfer, and contractility was determined in cardiomyocytes (cell shortening) and in vivo (fractional shortening). RESULTS: -NDPK-C was essential for the formation of a NDPK-B/G proteins complex. Protein and mRNA levels of NDPK-C were up-regulated in end-stage human HF, in rats following chronic isoprenaline (ISO) stimulation through osmotic minipumps, and after incubation of rat neonatal cardiomyocytes with ISO. ISO also promoted translocation of NDPK-C to the plasma membrane. Overexpression of NDPK-C in cardiomyocytes increased cAMP levels and sensitized cardiomyocytes to ISO-induced augmentation of contractility, whereas NDPK-C knockdown decreased cAMP levels. In vivo, depletion of NDPK-C in zebrafish embryos caused cardiac edema and ventricular dysfunction. NDPK-B knockout mice had unaltered NDPK-C expression, but showed contractile dysfunction and exacerbated cardiac remodeling during chronic ISO stimulation. In human end-stage HF, the complex formation between NDPK-C and Galphai2 was increased, whereas NDPK-C/Galphas interaction was decreased, producing a switch that may contribute to an NDPK-C-dependent cAMP-reduction in HF. CONCLUSIONS: -Our findings identify NDPK-C as an essential requirement for both the interaction between NDPK isoforms and with G proteins. NDPK-C is a novel critical regulator of beta-adrenoceptor/cAMP signaling and cardiac contractility. By switching from Galphas to Galphai2 activation, NDPK-C may contribute to lower cAMP levels and the related contractile dysfunction in HF.

KCa2.1, KCa2.2, KCa2.3, and KCa3.1 constitute a family of mammalian small- to intermediate-conductance potassium channels that are activated by calcium-calmodulin. KCa3.1 is unique among these four channels in that activation requires, in addition to calcium, phosphorylation of a single histidine residue (His358) in the cytoplasmic region, by nucleoside diphosphate kinase-B (NPDK-B). The mechanism by which KCa3.1 is activated by histidine phosphorylation is unknown. Histidine phosphorylation is well characterized in prokaryotes but poorly understood in eukaryotes. Here we demonstrate that phosphorylation of His358 activates KCa3.1 by antagonizing copper-mediated inhibition of the channel. Furthermore, we show that activated CD4+ T cells deficient in intracellular copper exhibit increased KCa3.1 histidine phosphorylation and channel activity, leading to increased calcium flux and cytokine production. These findings reveal a novel regulatory mechanism for a mammalian potassium channel and for T-cell activation, and highlight a unique feature of histidine versus serine/threonine and tyrosine as a regulatory phosphorylation site.

Whereas phosphorylation of serine, threonine, and tyrosine is exceedingly well characterized, the role of histidine phosphorylation in mammalian signaling is largely unexplored. Here we show that phosphoglycerate mutase family 5 (PGAM5) functions as a phosphohistidine phosphatase that specifically associates with and dephosphorylates the catalytic histidine on nucleoside diphosphate kinase B (NDPK-B). By dephosphorylating NDPK-B, PGAM5 negatively regulates CD4+ T cells by inhibiting NDPK-B-mediated histidine phosphorylation and activation of the K+ channel KCa3.1, which is required for TCR-stimulated Ca2+ influx and cytokine production. Using recently developed monoclonal antibodies that specifically recognize phosphorylation of nitrogens at the N1 (1-pHis) or N3 (3-pHis) positions of the imidazole ring, we detect for the first time phosphoisoform-specific regulation of histidine-phosphorylated proteins in vivo, and we link these modifications to TCR signaling. These results represent an important step forward in studying the role of histidine phosphorylation in mammalian biology and disease.

OBJECTIVE: The purpose of this article is to compare the effectiveness of a treatment algorithm for small renal tumors incorporating the nephrometry score, a renal tumor anatomy scoring system developed by urologists, with the current standard of uniformly recommended partial nephrectomy in patients with mild-to-moderate chronic kidney disease (CKD). MATERIALS AND METHODS: We developed a state-transition microsimulation model to project life expectancy (LE) in hypothetic patients with baseline mild or moderate CKD undergoing treatment of small renal masses. Our model incorporated the nephrometry score, which is predictive of postsurgical renal function loss. The two tested strategies were uniform treatment with partial nephrectomy and selective treatment based on nephrometry score and CKD stage, including percutaneous ablation for CKD stages 2 or 3a and intermediate-to-high nephrometry score or stage 3b CKD and any nephrometry score; otherwise, partial nephrectomy was assumed for other CKD stages and nephrometry scores. The model accounted for benign and malignant lesions, renal function decline, recurrence, and metastatic disease rates specific to each treatment, mortality by CKD stage, and comorbidities. Sensitivity analysis tested the stability of results when varying key parameters. RESULTS: Selective treatment with partial nephrectomy resulted in an average LE benefit of 0.48 year (95% interpercentile range, 0.42-0.54 year) in 65-year-old men and 0.37 year (95% interpercentile range, 0.30-0.43 year) in 65-year-old women relative to nondiscriminatory surgery, due to worsening CKD and cardiovascular mortality associated with partial nephrectomy. Model results were most sensitive to the rate of renal function decline and CKD-related mortality. CONCLUSION: Nephron-sparing treatment selection for small renal masses based on nephrometry score may improve LE in patients with mild or moderate CKD.

AIMS: Nucleoside diphosphate kinase B (NDPKB) is capable of maintaining the cellular nucleotide triphosphate pools. It might therefore supply UTP for the formation of UDP-GlcNAc from glucose. As NDPKB contributes to vascular dysfunction, we speculate that NDPKB might play a role in microangiopathies, such as diabetic retinopathy (DR). Therefore, we investigated the impact of NDPKB on retinal vascular damage using NDPKB-/- mice during development of DR and its possible mechanisms. METHODS: Pericyte loss and acellular capillary (AC) formation were assessed in streptozotocin-induced diabetic NDPKB-/- and wild-type (WT) mice. Expression of angiopoietin-2 (Ang2) and protein N-acetylglucosamine modification (GlcNAcylation) were assessed by western blot and/or immunofluorescence in the diabetic retinas as well as in endothelial cells depleted of NDPKB by siRNA and stimulated with high glucose. RESULTS: Similar to diabetic WT retinas, non-diabetic NDPKB-/- retinas showed a significant decrease in pericyte coverage in comparison with non-diabetic WT retinas. Hyperglycemia further aggravates pericyte loss in diabetic NDPKB-/- retinas. AC formation was detected in the diabetic NDPKB-/- retinas. Similar to hyperglycemia, NDPKB deficiency induced Ang2 expression and protein GlcNAcylation that were not further altered in the diabetic retinas. In cultured endothelial cells, stimulation with high glucose and NDPKB depletion comparably increased Ang2 expression and protein GlcNAcylation. CONCLUSIONS: Our data identify NDPKB as a protective factor in the retina, which controls Ang2 expression and the hexosamine pathway. NDPKB-deficient mice are a suitable model for studying mechanisms underlying diabetic retinal vascular damage.

OBJECTIVE: Vascular smooth muscle cells (VSMC) proliferation is a hallmark of atherosclerosis and vascular restenosis. The intermediate conductance Ca2+-activated K+ (SK4) channel is required for pathological VSMC proliferation. In T lymphocytes, nucleoside diphosphate kinase B (NDPKB) has been implicated in SK4 channel activation. We thus investigated the role of NDPKB in the regulation of SK4 currents (ISK4) in proliferating VSMC and neointima formation. APPROACH AND RESULTS: Function and expression of SK4 channels in VSMC from injured mouse carotid arteries were assessed by patch-clamping and real-time polymerase chain reaction. ISK4 was detectable in VSMC from injured but not from uninjured arteries correlating with the occurrence of the proliferative phenotype. Direct application of NDPKB to the membrane of inside-out patches increased ISK4, whereas NDPKB did not alter currents in VSMC obtained from injured vessels of SK4-deficient mice. The NDPKB-induced increase in ISK4 was prevented by protein histidine phosphatase 1, but not an inactive protein histidine phosphatase 1 mutant indicating that ISK4 is regulated via histidine phosphorylation in proliferating VSMC; moreover, genetic NDPKB ablation reduced ISK4 by 50% suggesting a constitutive activation of ISK4 in proliferating VSMC. In line, neointima formation after wire injury of the carotid artery was substantially reduced in mice deficient in SK4 channels or NDPKB. CONCLUSIONS: NDPKB to SK4 signaling is required for neointima formation. Constitutive activation of SK4 by NDPKB in proliferating VSMC suggests that targeting this interaction via, for example, activation of protein histidine phosphatase 1 may provide clinically meaningful effects in vasculoproliferative diseases such as atherosclerosis and post angioplasty restenosis.

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.