A role for ERK1/2 in EGF- and ATP-dependent regulation of amiloride-sensitive sodium absorption

Abstract

-Receptor-mediated inhibition of amiloride-sensitive sodium absorption was observed in primary and immortalized murine renal collecting duct cell (mCT12) monolayers. The addition of epidermal growth factor (EGF) to the basolateral bathing solution of polarized monolayers reduced amiloride-sensitive short-circuit current (I sc) by 15-25%, whereas the addition of ATP to the apical bathing solution decreased Isc by 40 -60%. Direct activation of PKC with phorbol 12-myristate 13-acetate (PMA) and mobilization of intracellular calcium with 2,5-di-tert-butyl-hydroquinone (DBHQ) reduced amiloride-sensitive I sc in mCT12 monolayers by 46 Ϯ 4% (n ϭ 8) and 22 Ϯ 2% (n ϭ 8), respectively. Exposure of mCT12 cells to EGF, ATP, PMA, and DBHQ caused an increase in phosphorylation of p42/p44 (extracellular signal-regulated kinase; ERK1/2). Pretreatment of mCT12 monolayers with an ERK kinase inhibitor (PD-98059; 30 M) prevented phosphorylation of p42/p44 and significantly reduced EGF, ATP, and PMA-induced inhibition of amiloride-sensitive I sc. In contrast, pretreatment of monolayers with a PKC inhibitor (bisindolylmaleimide I; GF109203x; 1 M) almost completely blocked the PMA-induced decrease in I sc, but did not alter the EGF-or ATP-induced inhibition of Isc. The DBHQ-mediated decrease in I sc was due to inhibition of basolateral Na ϩ -K ϩ -ATPase, but EGF-, ATP-, and PMA-induced inhibition was most likely due to reduced apical sodium entry (epithelial Na ϩ channel activity). The results of these studies demonstrate that acute inhibition of amiloride-sensitive sodium transport by extracelluar ATP and EGF involves ERK1/2 activation and suggests a role for MAP kinase signaling as a negative regulator of electrogenic sodium absorption in epithelia.mitogen-activated protein kinase; epithelial ion transport; epithelial sodium channel AMILORIDE-SENSITIVE Na ϩ transport, mediated by the epithelial Na ϩ channel (ENaC), is an important pathway for Na ϩ absorption by the colon and for Na ϩ retention by the distal nephron (16). A similar mechanism for Na ϩ transport is in the salivary duct, urinary bladder, sweat duct, and airway epithelium, where the process is responsible for the clearance of fetal lung liquid at birth (9, 28) and for control of the composition and/or depth of airway surface liquid in the postnatal lung (4). Defective regulation of ENaC and resultant Na ϩ hyperabsorption by the airway surface epithelium is thought to be an important component of the pathophysiology of cystic fibrosis (5). ENaC loss-of-function mutations (e.g., pseudohypoaldosteronism type I) are known to cause hyponatremia, hyperkalemia, and salt wasting, whereas gain-of-function mutations (e.g., salt-sensitive hypertension, Liddle's syndrome) lead to an increase in ENaC activity and excess Na ϩ reabsorption (20, 31).Corticosteroids, insulin, and vasopressin cause acute and/or chronic stimulation of sodium transport in epithelial cells (45) by several mechanisms, including alterations in ENaC open probability (23), increased synthesis of channel subunits...

Role of Epithelial Sodium Channels and Their Regulators in Hypertension

“…One of these is GILZ1 (glucocorticoid-induced leucine zipper protein 1), a small chaperone protein that has been found to stimulate ENaC surface expression by disrupting MAPK signaling (84,85). ENaC is inhibited by the Raf-MEK-ERK1/2 MAPK pathway (57,86,87). GILZ1 physically interacts with and inhibits Raf-1 (88, 89), leading to ENaC activation.…”

Purinergic signaling in the lumen of a normal nephron and in remodeled PKD encapsulated cysts

“…The higher amounts of extracellular ATP ligand are consistent with its effects on sodium (Na + ) and water (H 2 O) transport in renal collecting-duct epithelia and other ductal epithelia. Purinergic receptors attenuate epithelial sodium channel (ENaC)-mediated Na + absorption via multiple mechanisms [41][42][43][44][45][46]. In particular, Unwin and coworkers and Leipziger and colleagues have shown this elegantly in multiple in vivo, in-vivo-like, and in vitro model systems from kidney and other tissues [47][48][49][50].…”

Epithelial sodium channel regulated by differential composition of a signaling complex

“…A parallel and apparently distinct signaling cascade, the Raf-1-MAPK/ERK kinase (MEK)1/2-ERK1/2 (Raf-MEK-ERK) pathway, however, acts to inhibit cell surface ENaC through ERK1/2-dependent phosphorylation of the channel itself, which stimulates its interaction with Nedd4 (6)(7)(8)(9). Recent evidence supports the idea that the Raf-interacting protein glucocorticoid-induced leucine zipper protein 1 (GILZ1) increases plasma membrane ENaC in part by antagonizing the inhibitory effect of the Raf-MEK-ERK module (10,11).…”