The A-kinase anchoring protein 15 regulates feedback inhibition of the epithelial Na+ channel.
Protein kinase A anchoring proteins or AKAPs regulate the activity of many ion channels. Protein kinase A (PKA) is a well-recognized target of AKAPs, with other kinases now emerging as additional targets. We examined the roles of epithelial-expressed AKAPs in regulating the epithelial Na+ channel (ENaC). Experiments used heterologous expression with AKAP15, AKAP-KL, and AKAP79 in Xenopus oocytes. Experiments were carried out under high and low Na+ conditions, as Na+ loading is known to affect the baseline activity of ENaC in a PKC-dependent mechanism. ENaC activity was unaffected by AKAP79 and AKAP-KL expression. However, oocytes coexpressing AKAP15 exhibited an 80% and 91% reduction in the amiloride-sensitive, whole-cell conductance in high and low Na+ conditions, respectively. The reduced channel activity was unaffected by PKA activation or inhibition, indicating a PKA-independent mechanism. Expression with a membrane-targeting domain, mutant form of AKAP15 (AKAP15m) prevented the decrease of ENaC activity, but only under low Na+ conditions. In high sodium conditions, coexpression with AKAP15m led to an increase of ENaC activity to levels similar to those observed under low Na+. These results indicate that membrane-associated AKAP15 reduces ENaC activity whereas the cytoplasmically associated one may participate in the channel's feedback inhibition by intracellular Na+, a process known to involve PKC. This hypothesis was further confirmed in coexpression experiments, which demonstrated functional and physical interaction between AKAP15 and PKCalpha. We propose that AKAP15 regulates ENaC via a novel PKA-independent pathway.
Bengrine
Abderrahmane
A
Department of Physiology and Biophysics, SUNY at Buffalo, 3435 Main St., Buffalo, NY 14214, USA.
Li
Jinqing
J
Awayda
Mouhamed S
MS
D054758:A Kinase Anchor Proteins; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D025461:Feedback, Physiological; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D014981:Xenopus
D054758:A Kinase Anchor Proteins; C484688:AKAP2 protein, human; C487775:AKAP5 protein, human; C112596:AKAP7 protein, human; D048868:Adaptor Proteins, Signal Transducing; D053503:Epithelial Sodium Channels; D008565:Membrane Proteins; D012964:Sodium; D017868:Cyclic AMP-Dependent Protein Kinases