Abstract
Aquaporin-5 (AQP5) facilitates passive water transport in glandular epithelia in response to secretory stimuli via intracellular pathways involving calcium release, cAMP and protein kinase A (PKA). In epithelial plasma membranes, AQP5 may be acutely regulated to facilitate water transport in response to physiological stimuli by changes in protein modifications, interactions with proteins and lipids, nanoscale membrane domain organization, and turnover rates. Such regulatory mechanisms could potentially be associated with alteration of diffusion behavior, possibly resulting in a change in the plasma membrane diffusion coefficient of AQP5. We aimed to test the short-term regulatory effects of the above pathways, by measuring lateral diffusion of AQP5 and an AQP5 phospho-mutant, T259A, using k-space Image Correlation Spectroscopy of quantum dot- and EGFP-labeled AQP5. Elevated cAMP and PKA inhibition significantly decreased lateral diffusion of AQP5, whereas T259A mutation showed opposing effects; slowing diffusion without stimulation and increasing diffusion to basal levels after cAMP elevation. Thus, lateral diffusion of AQP5 is significantly regulated by cAMP, PKA, and T259 phosphorylation, which could be important for regulating water flow in glandular secretions.
Highlights
Epithelia are functional barriers lining exterior surfaces, tubes, and glands, allowing selective transport of water, ions, and other solutes [1].Aquaporin water channels (AQP) are homotetrameric transmembrane proteins which facilitate trans-epithelial water transport across plasma membranes in response to osmotic gradients. 13 mammalian homologs (AQP0-12) have been identified and are expressed in a widePLOS ONE | DOI:10.1371/journal.pone.0133324 July 28, 2015Regulation of AQP5 Diffusion
Besides long-term regulation of AQP5 plasma membrane abundance to facilitate water transport associated with glandular secretion, AQP5 could be regulated on a fast time-scale within epithelial plasma membranes by post-translational modifications, interactions with other proteins and lipids, and incorporation into microdomains which could modulate function and/or rate of accumulation and endocytosis/turn-over
In subconfluent MDCK AQP5-EGFP cells, AQP5-EGFP was distributed homogenously throughout the entire plasma membrane (Fig 1A) and the same localization pattern was observed in MDCK cells stably expressing AQP5-myc-EGFP (Fig 1B)
Summary
Epithelia are functional barriers lining exterior surfaces, tubes, and glands, allowing selective transport of water, ions, and other solutes [1].Aquaporin water channels (AQP) are homotetrameric transmembrane proteins which facilitate trans-epithelial water transport across plasma membranes in response to osmotic gradients. 13 mammalian homologs (AQP0-12) have been identified and are expressed in a widePLOS ONE | DOI:10.1371/journal.pone.0133324 July 28, 2015Regulation of AQP5 Diffusion. Epithelia are functional barriers lining exterior surfaces, tubes, and glands, allowing selective transport of water, ions, and other solutes [1]. Aquaporin water channels (AQP) are homotetrameric transmembrane proteins which facilitate trans-epithelial water transport across plasma membranes in response to osmotic gradients. 13 mammalian homologs (AQP0-12) have been identified and are expressed in a wide.
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