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, theGprotein gustducin couples TAS2R to phospholipase C; however, we find very low levels ofGagustmRNAor protein in HASM.Wehypothesized that anotherGprotein inHASM 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. a subunit expression in HASM was Gαi2.Gαi1=Gαi3. Gαtrans1≈Gatrans2, with Gagust and Gao at the limits of detection (.100-fold lower than Gai2). Small interfering RNA knockdowns in HASM showed losses of [Ca21]i and ERK1/2 signaling when Gai3, Gai2, orGai3 were reduced. Gαtrans1 and Gatrans2 knockdowns had no effect on [Ca21]i and a minimal, transient effect on ERK1/2 phosphorylation. Furthermore, Gαgust and Gαoknockdowns did not affect any TAS2R signaling. In overexpression experiments in human embryonic kidney-293T cells, we confirmed an agonistdependent physical interaction between TAS2R14 and Gai2. ASM cells from transgenic mice expressing a peptide inhibitor ofGαi2 had attenuated relaxation to TAS2R agonist. These data indicate that, unlike in taste cells, TAS2Rs couple to the prevalent G proteins, Gαi1, Gαi2, and Gai3, 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 Gagust, indicating that TAS2Rs can optionally couple to several G proteins in a cell type-dependent manner contingent upon G protein expression.
Original language | English (US) |
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Pages (from-to) | 762-771 |
Number of pages | 10 |
Journal | American journal of respiratory cell and molecular biology |
Volume | 56 |
Issue number | 6 |
DOIs | |
State | Published - Jun 2017 |
Externally published | Yes |
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Pulmonary and Respiratory Medicine
- Clinical Biochemistry
- Cell Biology
Keywords
- Airway smooth muscle
- Asthma
- Bitter taste receptors
- Chronic obstructive pulmonary disease
- G proteins