A Par3/LIM Kinase/Cofilin Pathway Mediates Human Airway Smooth Muscle Relaxation by TAS2R14.

Bitter taste receptors (TAS2Rs) are G protein-coupled receptors expressed on human airway smooth muscle (HASM) cells; when activated by receptor agonists they evoke marked airway relaxation. In both taste and HASM cells, TAS2Rs activate a canonical G βγ mediated stimulation of Ca 2+ release from intracellular stores by activation of phospholipase Cβ(PLCβ). Alone, this [Ca 2+ ] i signaling does not readily account for relaxation, particularly since bronchoconstrictive agonists acting at G q coupled receptors also increase [Ca 2+ ] i . We established that TAS2R14 activation in HASM promotes relaxation through F-actin severing. This destabilization of actin was from agonist-promoted activation (dephosphorylation) of cofilin, which was pertussis toxin sensitive. Cofilin dephosphorylation was due to TAS2R-mediated deactivation of LIM kinase. The link between early receptor action and the distal cofilin dephosphorylation was found to be the polarity protein Par3, a known binding partner with PLCβ that inhibits LIM kinase. The physiologic relevance of this pathway was assessed using knock-downs of cofilin and Par3 in HASM cells and in human precision cut lung slices. Relaxation by TAS2R14 agonists was ablated with knock-down of either protein as assessed by magnetic twisting cytometry in isolated cells or intact airways in the slices. Blocking [Ca 2+ ] i release by TAS2R14 inhibited agonist-promoted cofilin dephosphorylation, confirming a role for [Ca 2+ ] i in actin-modifying pathways. These results further elucidate the mechanistic basis of TAS2R-mediated HASM relaxation and point towards nodal points that may act as asthma or COPD disease/response modifiers or additional targets for novel bronchodilators. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).