Rapid activation of Na + /H + -exchange in MDCK cells by aldosterone involves MAP-kinases ERK 1/2

Abstract

The mineralocorticoid aldosterone is essential for the adequate regulation of electrolyte homeostasis, extracellular volume and blood pressure. As a steroid hormone it influences cellular functions by genomic actions. Previously it has been shown that aldosterone can activate Na+/H+-exchange (NHE) by a rapid, nongenomic mechanism. Because (1) NHE can be regulated by ERK1/2 (extracellular signal-regulated kinase) and (2) steroids have been reported to rapidly activate ERK1/2, we tested the hypothesis that activation of NHE by aldosterone involves ERK1/2, using MDCK-C11 cells. We show that nanomolar concentrations of aldosterone induce a rapid, non-genomic activation of NHE, which is characterized by an increased affinity for H+ with minor changes in the maximum transport rate. Accordingly, aldosterone led to an increase of cytosolic steady-state pH. The aldosterone-induced activation of NHE was prevented by the two specific inhibitors of ERK1/2 activation, PD 98059 (2.5 x 10(-5) mol/l) and U0126 (10(-5) mol/l). Furthermore, in the presence of U0126 there was no aldosterone-induced increase of steady-state pH. Finally, aldosterone induced a rapid phosphorylation of ERK1/2, indicating its ability to activate ERK1/2. The data presented here support the hypothesis that the rapid activation of NHE by aldosterone at nanomolar concentrations involves ERK1/2. Thus, in certain cell types, the MAPK cascade may represent an additional pathway mediating rapid aldosterone effects.

Aldosterone, Through Novel Signaling Proteins, Is a Fundamental Molecular Bridge Between the Genetic Defect and the Cardiac Phenotype of Hypertrophic Cardiomyopathy

“…The molecular mechanisms that regulate expression of CYP11B2 and production of aldosterone in the heart in general and in HCM in particular remain to be established. Aldosterone imparts a diverse array of biological effects comprising genomic (slow) and nongenomic (rapid) components, including but not limited to changes in the intracellular calcium concentration, 36 Na ϩ /H ϩ exchanger, 37 and activation of extracellular signal-regulated kinases p22/44, 25 phospholipase C, 23 and calcineurin. 24 The present findings implicate PKD and PI3K-p110␦ as the molecular mediators of cardiac hypertrophic and profibrotic effects and provide for novel mechanisms for the actions of aldosterone.…”

c-Src–Dependent Nongenomic Signaling Responses to Aldosterone Are Increased in Vascular Myocytes From Spontaneously Hypertensive Rats

“…9,11,18,29 Besides its well-known genomic actions, aldosterone induces rapid cellular responses by activating signaling pathways independently of genomic effects. [17][18][19][20][21][22][23][24][25][26][27][28][29] The protein tyrosine kinase c-Src is abundant in the vasculature and appears to be an important signaling molecule in VSMCs. c-Src induces activation of MAPKs (p38MAPK, c-Jun NH 2 -terminal kinase, and ERK1/2), which are associated with cell growth, apoptosis, and collagen deposition.…”

“…Aldosterone induces rapid cellular responses by modulating intracellular calcium (Ca 2ϩ ) and cAMP levels, Na ϩ /H ϩ exchanger activity, and phosphorylation of signaling molecules, including protein kinase C, epidermal growth factor receptor, and mitogen-activated protein kinases (MAPKs), including c-Jun NH 2 -terminal kinase, and extracellular signal-regulated kinases (ERKs) 1/2. [17][18][19][20][21][22][23][24][25][26][27][28] We recently demonstrated that aldosterone rapidly increases activation of p38 MAPK and NAD(P)H oxidase through c-Src-dependent pathways in vascular smooth muscle cells (VSMCs). In addition, the profibrotic action of aldosterone was dependent on c-Src-regulated p38 MAPK.…”

G Protein-Coupled Receptors-Induced Activation of Extracellular Signal-Regulated Protein Kinase (ERK) and Sodium-Proton Exchanger Type 1 (NHE1)

“…Specifically, they showed that expression of a dominant negative p44 ERK or of the MAPK phosphatase MKP-1, or treatment with the MEK1 inhibitor PD98059 reduced activation of NHE-1 by mixtures of growth factors by about 50%. Further, it has been shown that short-term activation of ERK leads to rapid stimulation of NHE1 in multiple cell types (erythrocytes, fibroblasts, MDCK-11 cells, rabbit skeletal muscle, and cultured rat neonatal and adult ventricular cardiomyocytes) when activated by diverse stimuli including growth factors, angiotensin II, and aldosterone (Wang et al, 1997;Sabri et al, 1998;Bouboula et al, 1999;Gekle et al, 2001;Wei et al, 2001;Moor et al, 2001;Snabaitis et al, 2002). At least in some cases, the short term-stimulation of NHE1 by ERK is mediated by phosphorylation of NHE1 either by ERK itself, or by p90RSK, an ERK-regulated kinase (Takahashi et al, 1999).…”

“…Indeed, in some cell types ERK plays a clear role in either the short or long term activation of NHE1 (Aharonovitz & Granot, 1996;Bianchini et al, 1997;Wang et al, 1997;Sabri et al, 1998;Bouaboula et al, 1999;Gekle et al, 2001). However, several groups were unable to demonstrate any role of ERK in regulation of NHE1 in a number of cell types (Gillis et al, 2001;Kang et al, 1998;Pederson et al, 2002;Garnovskaya et al, 1998;Di Sario et al, 2003).…”