Hypotonic stress upregulates β- and γ-ENaC expression through suppression of ERK by inducing MKP-1

Yue

American Journal of Physiology-Lung Cellular and Molecular Phys

et al. 2014

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We used a PKC-α knockout model to investigate the regulation of alveolar epithelial Na(+) channels (ENaC) by PKC. Primary alveolar type II (ATII) cells were subjected to cell-attached patch clamp. In the absence of PKC-α, the open probability (Po) of ENaC was decreased by half compared with wild-type mice. The channel density (N) was also reduced in the knockout mice. Using in vivo biotinylation, membrane localization of all three ENaC subunits (α, β, and γ) was decreased in the PKC-α knockout lung, compared with the wild-type. Confocal microscopy of lung slices showed elevated levels of reactive oxygen species (ROS) in the lungs of the PKC-α knockout mice vs. the wild-type. High levels of ROS in the knockout lung can be explained by a decrease in both cytosolic and mitochondrial superoxide dismutase activity. Elevated levels of ROS in the knockout lung activates PKC-δ and leads to reduced dephosphorylation of ERK1/2 by MAP kinase phosphatase, which in turn causes increased internalization of ENaC via ubiquitination by the ubiquitin-ligase Nedd4-2. In addition, in the knockout lung, PKC-δ activates ERK, causing a decrease in ENaC density at the apical alveolar membrane. PKC-δ also phosphorylates MARCKS, leading to a decrease in ENaC Po. The effects of ROS and PKC-δ were confirmed with patch-clamp experiments on isolated ATII cells in which the ROS scavenger, Tempol, or a PKC-δ-specific inhibitor added to patches reversed the observed decrease in ENaC apical channel density and Po. These results explain the decrease in ENaC activity in PKC-α knockout lung.

Section: Less Absorptionmentioning

confidence: 99%

ENaC activity and expression is decreased in the lungs of protein kinase C-α knockout mice

Yue

American Journal of Physiology-Lung Cellular and Molecular Phys

et al. 2014

Self Cite

American Journal of Physiology-Renal Physiology

“…DUSPs have been implicated as major modulators of signaling pathways affecting various physiological processes (11). A recent study showed that hypotonic stress stimulates ␤-epithelial sodium channel (ENaC) and ␥-ENaC mRNA expression through suppression of ERK by inducing MKP-1 (28). DUSP6, also known as MAP kinase phosphatase 3 (MKP-3), is specifically responsible for ERK1/2 dephosphorylation (1, 26).…”

mentioning

confidence: 99%

Aldosterone modulates thiazide-sensitive sodium chloride cotransporter abundance via DUSP6-mediated ERK1/2 signaling pathway

Zhang

Shao

et al. 2015

modulates thiazide-sensitive sodium chloride cotransporter abundance via DUSP6-mediated ERK1/2 signaling pathway. Am J Physiol Renal Physiol 308: F1119 -F1127, 2015. First published March 11, 2015 doi:10.1152/ajprenal.00543.2014.-Thiazide-sensitive sodium chloride cotransporter (NCC) plays an important role in maintaining blood pressure. Aldosterone is known to modulate NCC abundance. Previous studies reported that dietary salts modulated NCC abundance through either WNK4 [with no lysine (k) kinase 4]-SPAK (Ste20-related proline alanine-rich kinase) or WNK4-extracellular signalregulated kinase-1 and -2 (ERK1/2) signaling pathways. To exclude the influence of SPAK signaling pathway on the role of the aldosterone-mediated ERK1/2 pathway in NCC regulation, we investigated the effects of dietary salt changes and aldosterone on NCC abundance in SPAK knockout (KO) mice. We found that in SPAK KO mice low-salt diet significantly increased total NCC abundance while reducing ERK1/2 phosphorylation, whereas high-salt diet decreased total NCC while increasing ERK1/2 phosphorylation. Importantly, exogenous aldosterone administration increased total NCC abundance in SPAK KO mice while increasing DUSP6 expression, an ERK1/2-specific phosphatase, and led to decreasing ERK1/2 phosphorylation without changing the ratio of phospho-T53-NCC/total NCC. In mouse distal convoluted tubule (mDCT) cells, aldosterone increased DUSP6 expression while reducing ERK1/2 phosphorylation. DUSP6 Knockdown increased ERK1/2 phosphorylation while reducing total NCC expression. Inhibition of DUSP6 by (E)-2-benzylidene-3-(cyclohexylamino)-2,3-dihydro-1H-inden-1-one increased ERK1/2 phosphorylation and reversed the aldosterone-mediated increments of NCC partly by increasing NCC ubiquitination. Therefore, these data suggest that aldosterone modulates NCC abundance via altering NCC ubiquitination through a DUSP6-dependent ERK1/2 signal pathway in SPAK KO mice and part of the effects of dietary salt changes may be mediated by aldosterone in the DCTs. aldosterone; dietary salt; sodium chloride cotransporter; dual-specificity protein phosphatase 6; ERK1/2; SPAK KO mice THE THIAZIDE-SENSITIVE SODIUM chloride cotransporter (NCC), located in the apical membrane of the distal convoluted tubule (DCT) of the kidney, is responsible for 5-7% of sodium reabsorption (6). NCC plays a key role in the regulation of blood pressure and electrolytes homeostasis (6, 12). Loss-offunction mutations in NCC have been reported to cause Gitelman's syndrome (GS), which is characterized by salt-wasting and low blood pressure (15). NCC is known to be modulated by two different types of regulation, type 1-altering its membrane expression, and type 2-altering the transporter kinetics (17).Aldosterone has been shown to increase the thiazide-sensitive NCC protein in rats (20). Previous studies reported that the regulation of NCC by aldosterone is mediated through a WNK4 [with no lysine (k) kinase 4]-SPAK (Ste20-related proline alanine-rich kinase)-dependent pathway in response to the di...

“…Both lack of effect [64] and a positive effect of JNK1/2 [55] on NFAT5 have been reported. Like the effect on p38, hypotonicity also increases phosphorylation of ERK1/2 in human keratinocytes [73] , mIMCD3 cells [77] , renal epithelial A6 cells [72] , although inhibition of ERK by hypotonic stress in A6 cells was also reported [78] . Therefore, the mechanism for how ERK1/2 contributes to tonicity-dependent activation of NFAT5 remains to be elucidated.…”

Section: Potential Clinical Significance Of This Reviewmentioning

confidence: 89%

How do kinases contribute to tonicity-dependent regulation of the transcription factor NFAT5?

Zhou

2016

WJN

NFAT5 plays a critical role in maintaining the renal functions. Its dis-regulation in the kidney leads to or is associated with certain renal diseases or disorders, most notably the urinary concentration defect. Hypertonicity, which the kidney medulla is normally exposed to, activates NFAT5 through phosphorylation of a signaling molecule or NFAT5 itself. Hypotonicity inhibits NFAT5 through a similar mechanism. More than a dozen of protein and lipid kinases have been identified to contribute to tonicity-dependent regulation of NFAT5. Hypertonicity activates NFAT5 by increasing its nuclear localization and transactivating activity in the early phase and protein abundance in the late phase. The known mechanism for inhibition of NFAT5 by hypotonicity is a decrease of nuclear NFAT5. The present article reviews the effect of each kinase on NFAT5 nuclear localization, transactivation and protein abundance, and the relationship among these kinases, if known. Cyclosporine A and tacrolimus suppress immune reactions by inhibiting the phosphatase calcineurin-dependent activation of NFAT1. It is hoped that this review would stimulate the interest to seek explanations from the NFAT5 regulatory pathways for certain clinical presentations and to explore novel therapeutic approaches based on the pathways. On the basic science front, this review raises two interesting questions. The first one is how these kinases can specifically signal to NFAT5 in the context of hypertonicity or hypotonicity, because they also regulate other cellular activities and even opposite activities in some cases. The second one is why these many kinases, some of which might have redundant functions, are needed to regulate NFAT5 activity. This review reiterates the concept of signaling through cooperation. Cells need these kinases working in a coordinated way to provide the signaling specificity that is lacking in the individual one. Redundancy in regulation of NFAT5 is a critical strategy for cells to maintain robustness against hypertonic or hypotonic stress. Core tip: NFAT5 is critical for kidney functions. Its disregulation results in or is associated with the renal diseases and disorders. More than a dozen of kinases have been identified to contribute to tonicity-dependent regulation of NFAT5. The present review is focused on how these kinases regulate NFAT5 activity under the context of hypertonicity or hypotonicity. Understanding these regulatory mechanisms will have therapeutic implications. A precedent example is that recognition of the cyclosporine immunosuppressive effect resulted from inhibition of the phosphatase calcineurin-dependent activation of NFAT1 allows combination use of cyclosporine with other mechanistically different immunosuppressants to improve their therapeutic efficacy and reduce their side effects.Zhou X. How do kinases contribute to tonicity-dependent regulation of the transcription factor NFAT5? World J Nephrol 2016; 5(1): 20-32 Available from: