cAMP-stimulated Na⁺transport in H441 distal lung epithelial cells: role of PKA, phosphatidylinositol 3-kinase, and sgk1

Abstract

H441 cells, a bronchiolar epithelial cell line, develop a cAMP-regulated benzamil-sensitive Na+ transport pathway on permeable supports (Itani OA, Auerbach SD, Husted RF, Volk KA, Ageloff S, Knepper MA, Stokes JB, Thomas CP. Am J Physiol Lung Cell Mol Physiol 282: L631-L641, 2002). To understand the molecular basis for the stimulation of Na+ transport, we delineated the role of specific intracellular pathways and examined the effect of cAMP on alphabetagamma-epithelial Na+ channel (ENaC) and sgk1 expression. Na+ transport increases within 5 min of cAMP stimulation and is sustained for >24 h. The sustained effect of cAMP on Na+ transport is abolished by LY-294002, an inhibitor of phosphatidylinositol 3-kinase, by H89, an inhibitor of PKA, or by SB-202190, an inhibitor of p38 MAP kinase. The sustained effect of cAMP was associated with increases in alpha-ENaC mRNA and protein but without a detectable increase in betagamma-ENaC and sgk1. The early effect of cAMP on Na+ transport is brefeldin sensitive and is mediated via PKA. These results are consistent with a model where the early effect of cAMP is to increase trafficking of Na+ channels to the apical cell surface whereas the sustained effect requires the synthesis of alpha-ENaC.

The regulation of selective and nonselective Na+ conductances in H441 human airway epithelial cells

“…This was surprising since previous studies of H441 cells indicated that PI3K played a central role in the control of Na ϩ transport (51). However, the cells used in this earlier study displayed a Na ϩ -absorbing phenotype under basal conditions (51), whereas, in our hands, G Na is negligible in hormonedeprived cells (see also Ref.…”

“…These observations are consistent with a body of data that highlights SGK1 as an important regulator of G Na in absorptive epithelia (1-3, 31, 49 -51, 53, 57). Although it is clear that glucocorticoid hormones do induce SGK1 expression (31), SGK1 is an important downstream target of PI3K (29), and data from several absorptive cell types have suggested that insulin can increase the apical abundance of ENaC via a mechanism dependent on a PI3K-mediated increase in SGK1 activity (2,8,46,51). Moreover, PIP 2 and PIP 3 also activate ENaC by binding to the channel complex, and this provides another mechanism by which PI3K-coupled agonists, such as insulin, can stimulate Na ϩ transport (20,42,43,52).…”

Glucose homeostasis across human airway epithelial cell monolayers: role of diffusion, transport and metabolism

“…When cultured at air interface, these cells form an absorptive epithelial monolayer, exhibit vectorial ion transport processes and have similar morphological and phenotypic characteristics to primary cultured human airway epithelial cells (HBEC) and in vivo human airway [4,8,19]. Therefore, they have been used by us and a number of other researchers as a model of absorptive human airway epithelium [25,36,41,42]. The aim of this study was to use H441 cell monolayers to explore the process by which glucose diffuses across airway epithelium, to identify the function of GLUT transporters and the role of glucose metabolism in maintaining low glucose concentrations in human ASL.…”

Modulation of epithelial sodium channel in human alveolar epithelial cells by lipoxin A4 through AhR-cAMP-dependent pathway

“…Studies have shown that AhR induces signaling pathways that entail ERK, PKA, MMP9 and cAMP, cGMP and Ca 2+ [22]. It has also been shown that AhR is more sensitive to the cAMP signaling pathway [22,23], and that cAMP induces nuclear translocation of the AhR [24]. Thus it appears that the two signaling pathways for regulation of ENaC, cAMP, and cGMP are compartmentalized.…”