Real-time three-dimensional imaging of lipid signal transduction: apical membrane insertion of epithelial Na<sup>+</sup> channels

Blazer‐Yost, Bonnie L.; Vahle, Judith C.; Byars, Jason M.; Bacallao, Robert L.

doi:10.1152/ajpcell.00226.2004

Cited by 51 publications

(45 citation statements)

References 40 publications

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“…However, PI(3,4,5)P 3 should first be produced in the inner leaflet of the basolateral membrane and then diffused in the inner leaflet to the apical membrane because the PI3K inhibitor LY294002 was added to the basolateral bath. This hypothesis is supported by previous studies, which showed that PI(3,4,5)P 3 can laterally diffuse in the inner leaflet of epithelial cell membranes from the basolateral membrane domain, where it is generated, to the apical membrane domain (30). Theoretically, the apical PI(3,4,5)P 3 would be rapidly degraded because the lipid phosphatase PTEN (phosphatase and tensin homolog) is located in the apical membrane (31).…”

Section: Discussionsupporting

confidence: 71%

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Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

2011

Journal of Biological Chemistry

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ENaC 2 in the distal nephron plays an important role in maintaining Na ϩ homeostasis and consequently controls systemic blood pressure. Excess sodium reabsorption due to enhanced ENaC activity can lead to hypertension, as is seen in Liddle syndrome (1, 2) and other genetic diseases (3). Surprisingly, whether high salt intake induces hypertension by targeting ENaC has not been examined. High salt intake can elevate both superoxide (O 2 . ) (4, 5) and H 2 O 2 (6) in the kidney by stimulating NAD(P)H oxidase (7-9), and O 2 . can increase aldosterone-me- , stimulate the non-receptor tyrosine kinase, c-Src (15). c-Src is known to be directly associated with p85, the regulatory subunit of PI3K (16). Tyrosine phosphorylation of p85 reduces its inhibitory effect on PI3K (17). These studies indicate that ROS may stimulate PI3K and consequently promote the synthesis of PI(3,4,5)P 3 . We (18 -20) and others (21,22) have previously shown that PI(3,4,5)P 3 stimulates ENaC. Taken together, these studies suggest that H 2 O 2 may stimulate ENaC by elevating PI(3,4,5)P 3 through activation of PI3K. In the present study, using patch clamp techniques combined with confocal microscopy analysis of apical PI(3,4,5)P 3 levels, we show that H 2 O 2 stimulates ENaC in A6 distal nephron cells via PI3K-dependent elevation of PI(3,4,5)P 3 in the apical membrane. MATERIALS AND METHODSCell Culture-Xenopus A6 distal nephron cells were purchased from the American Type Culture Collection (Manassas, VA). Under previously used culture conditions, basal activity of ENaC in A6 cells is relatively high (23). It is difficult to see and analyze any stimulatory effect when basal ENaC activity is high. Therefore, in the present study, we modified the culture medium to reduce basal ENaC activity. The medium contained 2 parts of DMEM/F-12 (1:1) medium (Invitrogen), 1 part of H 2 O, 15 mM NaHCO 3 (total Na ϩ ϭ 101 mM, which is ideal for amphibian A6 cells), 2 mM L-glutamine, 10% fetal bovine serum (Invitrogen), 25 units/ml penicillin, 25 units/ml streptomycin. A6 cells were cultured in plastic flasks in the presence of 1 M aldosterone at 26°C and 4% CO 2 . After the cells became 70% * This work was supported, in whole or in part, by National Institutes of Health Grant 5R01-DK067110 (to H.-P. M.

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Section: Discussionsupporting

confidence: 71%

“…Previous studies suggested that PI(3,4,5)P 3 is produced in the inner leaflet of the basolateral membrane and can freely diffuse in the inner leaflet to reach the apical membrane (30). Therefore, the PI3K inhibitor was added to the basolateral bath.…”

Section: Inhibition Of Pi3k Abolishes the Effect Of H 2 O 2 On Enac Pmentioning

confidence: 99%

Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

2011

Journal of Biological Chemistry

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“…The effects of aldosterone and insulin or IGF-1 may be additive [17]. Insulin stimulates SGK1 and is thus expected to enhance ENaC activity and renal Na + reabsorption [6][7][8]. SGK1 contributes to the regulation of renal Na + excretion by aldosterone, insulin, and IGF-1.…”

Section: Discussionmentioning

confidence: 99%

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARγ agonist pioglitazone

Artunc

Sandulache

Nasir

et al. 2008

Pflugers Arch - Eur J Physiol

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PPARγ-agonists enhance insulin sensitivity and improve glucose utilization in diabetic patients. Adverse effects of PPARγ-agonists include volume retention and edema formation. Recent observations pointed to the ability of PPARγ agonists to enhance transcription of the serum and glucocorticoid-inducible kinase SGK1, a kinase that is genomically upregulated by mineralocorticoids and stimulates various renal channels and transporters including the renal epithelial Na + channel ENaC. SGK1 has been proposed to mediate the volume retention after treatment with PPARγ agonists. To test this hypothesis, food containing the PPARγ agonist pioglitazone (0.02%, i.e., approximately 25 mg/kg bw/day) was administered to gene-targeted mice lacking SGK1 (sgk1 −/− , n=12) and their wild-type littermates (sgk1 +/+ , n=12). According to in situ hybridization, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence, treatment with pioglitazone significantly increased renal SGK1 mRNA and protein expression in sgk1 +/+ mice. The treatment increased body weight significantly in both, sgk1 +/+ mice (+2.2±0.3 g) and sgk −/− mice (+1.3±0.2 g), and decreased hematocrit significantly in sgk1 +/+ mice (−6.5±1.0%) and sgk1 −/− mice (−3.1±0.6%). Both effects were significantly (p<0.05) more pronounced in sgk1 +/+ mice. According to Evans Blue

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“…Because insulin also elevates ENaC activity via PI 3-K (28,42), PIP 3 likely also mediates the regulation of ENaC by insulin (43,44).…”

Section: Stimulation Of Steroid Receptors Increases Membrane Pip 3 Anmentioning

confidence: 99%

“…Using this method, recent studies have shown that there is an obvious elevation of apical membrane PIP 3 in response to insulin (43). We recently demonstrated that both PIP 3 and the N-terminal tail of ␥-ENaC are required for aldosteroneinduced ENaC activity and trafficking (62).…”

Section: Possible Role Of Pip 2 and Pip 3 In Receptormediated Enac Rementioning

confidence: 99%

Acute Regulation of Epithelial Sodium Channel by Anionic Phospholipids

Eaton

2005

Journal of the American Society of Nephrology

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Anionic phospholipids such as phosphatidylinositol 4,5-bisphosphate (PIP 2 ) and phosphatidylinositol 3,4,5-trisphosphate (PIP 3 ) are normally located in the inner leaflet of the plasma membrane, where these anionic phospholipids can regulate transmembrane proteins, including ion channels and transporters. Recent work has demonstrated that (1) ATP inhibits the renal epithelial sodium channel (ENaC) via a phospholipase C-dependent pathway that reduces PIP 2 , (2) aldosterone stimulates ENaC via phosphoinositide 3-kinase, and (3) PIP 2 and PIP 3 regulate ENaC. Several lines of evidence show that ATP stimulation of purinergic P2Y receptors hydrolyzes PIP 2 and that aldosterone stimulation of steroid receptors induces PIP 3 formation. These studies together suggest that one primary mechanism for regulating ENaC is by alteration of anionic phospholipids and that the receptor-mediated and hormonal regulation of ENaC works through a variety of signaling pathways, but many of these pathways finally alter ENaC activity by regulating the formation or degradation of anionic phospholipids. Therefore, changes in the concentration of PIP 2 and PIP 3 are hypothesized to participate in the regulation of ENaC by purinergic and corticoid receptors. The underlying mechanism may be associated with a physical interaction of the positively charged cytoplasmic domains of the ␤-and ␥-ENaC with the negatively charged membrane phospholipids. The exact nature of this interaction will require further investigation. T he phospholipid compositions of the two leaflets of the lipid bilayer that forms the plasma membrane are strikingly different. Anionic phospholipids are normally located in the inner leaflet to form a negatively charged surface. However, whether the phospholipid asymmetry affects the function of transmembrane proteins remains largely unknown. Recent studies have shown that one of the anionic phospholipids, phosphatidylinositol 4,5-bisphosphate (PIP 2 ), regulates Na ϩ -Ca 2ϩ exchangers and inward rectifier potassium channels (1-4). Besides PIP 2 , phosphatidylinositol 3,4,5-trisphosphate (PIP 3 ), regulates ATP-sensitive potassium (K ATP ) channels (5,6). A model for the regulation of K ATP channels by anionic phospholipids has been proposed; the negatively charged head group of PIP 2 or PIP 3 locks the positively charged carboxyl terminus of K ATP channels in an open conformation and prevents ATP binding to the cytosolic terminus (7). These recent studies suggest that anionic phospholipids may interact with the positively charged cytoplasmic termini of other ion channels and transporters. In this review, we focus primarily on the mechanism by which changes in cellular anionic phospholipids such as PIP 2 and PIP 3 regulate the renal epithelial sodium channel (ENaC) and then speculate on a possible underlying mechanism. Stimulation of Purinergic P2Y Receptors Decreases Membrane PIP 2 and ENaC ActivityIt is known that ATP binds to the purinergic P2Y receptor family, G protein-coupled receptors that activate phospholipase C (PLC...

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Real-time three-dimensional imaging of lipid signal transduction: apical membrane insertion of epithelial Na⁺ channels

Cited by 51 publications

References 40 publications

Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARγ agonist pioglitazone

Acute Regulation of Epithelial Sodium Channel by Anionic Phospholipids

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Real-time three-dimensional imaging of lipid signal transduction: apical membrane insertion of epithelial Na+ channels

Cited by 51 publications

References 40 publications

Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

Hydrogen Peroxide Stimulates the Epithelial Sodium Channel through a Phosphatidylinositide 3-Kinase-dependent Pathway

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARγ agonist pioglitazone

Acute Regulation of Epithelial Sodium Channel by Anionic Phospholipids

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Real-time three-dimensional imaging of lipid signal transduction: apical membrane insertion of epithelial Na⁺ channels