Editors' ChoiceATP Signaling

A “Swell” Way to Regulate Pannexin-Mediated ATP Release

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Science Signaling  02 Aug 2011:
Vol. 4, Issue 184, pp. ec217
DOI: 10.1126/scisignal.4184ec217

Release of adenosine triphosphate (ATP), and the subsequent activation of airway epithelial cell purinergic receptors and downstream pathways involved in regulating ciliary beat frequency, contributes to lung innate defense mechanisms such as mucociliary clearance of particles and pathogens from airways. Under hypotonic conditions, such as might be encountered in the presence of pathogen-stimulated hypotonic gland secretions, pannexin 1, a plasma membrane hemichannel, mediates ATP release from cultured human airway epithelial cells. Hypotonic conditions lead to cell swelling and, consequently, to mechanical strain. Here, Seminario-Vidal et al. have identified a role for transient receptor potential vanilloid 4 (TRPV4) ion channels, which can sense osmotic stress, and the small guanosine triphosphatase (GTPase) RhoA, which can be activated by mechanical strain, upstream of pannexin 1 in promoting hypotonic stress–induced ATP release. Perfusion assays performed under hypotonic conditions revealed a reduced luminal ATP concentration (measured using a luciferase assay) in tracheas excised from pannexin 1 knockout mice compared with that in tracheas excised from wild-type littermates. Hypotonic stress–induced uptake of propidium iodide, a pannexin channel–permeable reporter dye, was also reduced in primary cultures of mouse tracheal epithelial (MTE) cells from pannexin 1 knockout mice but not in wild-type MTE cells. Pull-down assays using lysates from well-differentiated human bronchial epithelial (WD-HBE) cells revealed an increase in GTP-bound RhoA, indicative of its activation, in response to hypotonic treatment. Pharmacological inhibition of Rho kinase or myosin light chain kinase, downstream components of RhoA signaling, in WD-HBE cells or expression of a RhoA dominant-negative construct in A459 lung epithelial carcinoma cells reduced propidium iodide uptake and ATP release in response to hypotonic stress. Moreover, pharmacological inhibition of TRPV4 reduced the amount of propidium iodide uptake, ATP release, and RhoA activation induced by hypotonic treatment of WD-HBE cells. Together, the data suggest that RhoA signaling links osmotic swelling–induced strain sensed by TRPV4 to pannexin 1–mediated ATP release in airway epithelial cells.

L. Seminario-Vidal, S. F. Okada, J. I. Sesma, S. M. Kreda, C. A. van Heusden, Y. Zhu, L. C. Jones, W. K. O’Neal, S. Penuela, D. W. Laird, R. C. Boucher, E. R. Lazarowski, Rho signaling regulates pannexin 1-mediated ATP release from airway epithelia. J. Biol. Chem. 286, 26277–26286 (2011). [Abstract] [Full Text]

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