Regulation of epithelial sodium channels by cGMP/PKGII

Abstract

Airway and alveolar fluid clearance is mainly governed by vectorial salt movement via apically located rate-limiting Na + channels (ENaC) and basolateral Na + /K + -ATPases. ENaC is regulated by a spectrum of protein kinases, i.e. protein kinase A (PKA), C (PKC), and G (PKG). However, the molecular mechanisms for the regulation of ENaC by cGMP/PKG remain to be elucidated. In the present study, we studied the pharmacological responses of native epithelial Na + channels in human Clara cells and human αβγδ ENaCs expressed in oocytes to cGMP. 8-pCPT-cGMP increased amiloride-sensitive short-circuit current (I sc ) across H441 monolayers and heterologously expressed αβγδ ENaC activity in a dose-dependent manner. Similarly, 8-pCPT-cGMP (a PKGII activator) but not 8-Br-cGMP (a PKGI activator) increased amiloride-sensitive whole cell currents in H441 cells in the presence of CFTRinh-172 and diltiazem. In all cases, the cGMP-activated Na + channel activity was inhibited by Rp-8-pCPT-cGMP, a specific PKGII inhibitor. This was substantiated by the evidence that PKGII was the sole isoform expressed in H441 cells at the protein level. Importantly, intratracheal instillation of 8-pCPT-cGMP in BALB/c mice increased amiloride-sensitive alveolar fluid clearance by ∼30%, consistent with the in vitro results. We therefore conclude that PKGII is an activator of lung epithelial Na + channels, which may expedite the resolution of oedematous fluid in alveolar sacs.

8-(4-Chlorophenylthio)-Guanosine-3′,5′-Cyclic Monophosphate-Na Stimulates Human Alveolar Fluid Clearance by Releasing External Na+ Self-Inhibition of Epithelial Na+ Channels

“…CPT-cGMP, but not parent cGMP, acutely activated human ENaC activity as an external ligand (19,26). The aim of this study was to examine whether CPT-cGMP could be used as a pharmaceutical strategy to up-regulate alveolar fluid clearance (AFC) via stimulating ENaC and its underlying mechanisms.…”

“…A mutation (a F61L ) at the amino terminal of the protein, adjacent to the gating tract in the M1 domain, enhanced self-inhibition (25). Our current understanding of the nature of ENaC gating mechanisms provides no unequivocal answers to the question of how the aforementioned domains affect self-inhibition.CPT-cGMP, but not parent cGMP, acutely activated human ENaC activity as an external ligand (19,26). The aim of this study was to examine whether CPT-cGMP could be used as a pharmaceutical strategy to up-regulate alveolar fluid clearance (AFC) via stimulating ENaC and its underlying mechanisms.…”

Type II cyclic guanosine monophosphate-dependent protein kinase inhibits epidermal growth factor receptor activation in different cancer cell lines

“…However, novel functions of PKG II have been identified, including an involvement in mechano-signal transduction in osteoblasts, and in the regulation of sodium channels (20,21). In addition, previous studies have indicated that PKG II may be a potential cancer suppressor due to its role in the regulation of proliferation and apoptosis in cancer cells (22,23).…”

Type II cGMP-dependent protein kinase inhibits EGF-induced MAPK/JNK signal transduction in breast cancer cells

“…However, recent data show that this kinase has some new functions: Nie et al (18) found that PKGII regulated epithelial sodium channels; Rangaswami et al (19,20) reported that PKGII had an important role in mechano-transduction of osteoblast. A more important finding in research of PKGII is that this kinase has a role in regulating proliferation and apoptosis of cells and is potentially associated with tumorigenesis.…”