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Coupling of Airway Smooth Muscle Bitter Taste Receptors to Intracellular Signaling and Relaxation Is via Gαi1,2,3.


ABSTRACT: Bitter taste receptors (TAS2Rs) are expressed on human airway smooth muscle (HASM) and evoke marked relaxation. Agonist interaction with TAS2Rs activates phospholipase C and increases compartmentalized intracellular Ca2+ ([Ca2+]i) via inositol 1,4,5 triphosphate. In taste cells, the G protein gustducin couples TAS2R to phospholipase C; however, we find very low levels of Gαgust mRNA or protein in HASM. We hypothesized that another G protein in HASM transmits TAS2R function. TAS2R signaling to [Ca2+]i, extracellular signal-regulated kinase (ERK) 1/2, and physiologic relaxation was sensitive to pertussis toxin, confirming a role for a member of the Gi family. α subunit expression in HASM was Gαi2 > Gαi1 = Gαi3 > Gαtrans1 ≈ Gαtrans2, with Gαgust and Gαo at the limits of detection (>100-fold lower than Gαi2). Small interfering RNA knockdowns in HASM showed losses of [Ca2+]i and ERK1/2 signaling when Gαi1, Gαi2, or Gαi3 were reduced. Gαtrans1 and Gαtrans2 knockdowns had no effect on [Ca2+]i and a minimal, transient effect on ERK1/2 phosphorylation. Furthermore, Gαgust and Gαo knockdowns did not affect any TAS2R signaling. In overexpression experiments in human embryonic kidney-293T cells, we confirmed an agonist-dependent physical interaction between TAS2R14 and Gαi2. ASM cells from transgenic mice expressing a peptide inhibitor of Gαi2 had attenuated relaxation to TAS2R agonist. These data indicate that, unlike in taste cells, TAS2Rs couple to the prevalent G proteins, Gαi1, Gαi2, and Gαi3, with no evidence for functional coupling to Gαgust. This absence of function for the "canonical" TAS2R G protein in HASM may be due to the very low expression of Gαgust, indicating that TAS2Rs can optionally couple to several G proteins in a cell type-dependent manner contingent upon G protein expression.

SUBMITTER: Kim D 

PROVIDER: S-EPMC5516295 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Coupling of Airway Smooth Muscle Bitter Taste Receptors to Intracellular Signaling and Relaxation Is via G<sub>αi1,2,3</sub>.

Kim Donghwa D   Woo Jung A JA   Geffken Ezekiel E   An Steven S SS   Liggett Stephen B SB  

American journal of respiratory cell and molecular biology 20170601 6


Bitter taste receptors (TAS2Rs) are expressed on human airway smooth muscle (HASM) and evoke marked relaxation. Agonist interaction with TAS2Rs activates phospholipase C and increases compartmentalized intracellular Ca<sup>2+</sup> ([Ca<sup>2+</sup>]<sub>i</sub>) via inositol 1,4,5 triphosphate. In taste cells, the G protein gustducin couples TAS2R to phospholipase C; however, we find very low levels of G<sub>αgust</sub> mRNA or protein in HASM. We hypothesized that another G protein in HASM tra  ...[more]

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