Journal Article

TAS2R5 screening reveals biased agonism that fails to evoke internalization and downregulation resulting in attenuated desensitization

Kim, Donghwa, Liggett, Stephen B., Strzelinski, Hannah R.

2025

Overview

The bitter taste receptor type 5 (TAS2R5) is expressed on multiple cell types and appears to be a suitable target for novel agonist treatments across multiple therapeutic areas. Like most G protein coupled receptors (GPCRs), TAS2R5 undergoes functional desensitization with prolonged agonist exposure which could limit effectiveness. The net loss of cellular receptors (termed downregulation) is a prominent mechanism of long-term desensitization; we screened 13 agonists for downregulation of receptor protein in TAS2R5-transfected HEK-293T and airway smooth muscle cells in culture, searching for pathway selectivity favoring G protein coupling over downregulation. The benchmark agonist 1,10-phenanthroline (denoted T5-1) evoked as much as 75% downregulation of TAS2R5 protein expression with 18-24 hrs of agonist exposure, while an analogue of T5-1 (denoted T5-12) caused a 2-3 fold increase in expression. Functionally, T5-1 and T5-12 were found to be full agonists when measuring [Ca 2+ ] i or ERK1/2 stimulation. The T5-12 phenotype was found to be due to agonist-induced stabilization of the receptor confining it to the cell membrane with subsequent failure to undergo internalization and receptor degradation. This occurred despite normal (referenced to T5-1) GRK-mediated receptor phosphorylation and β-arrestin recruitment by T5-12. Consistent with the lack of downregulation, T5-12 evoked much less functional desensitization of the [Ca 2+ ] i (43% vs 78%) and ERK1/2 (64% vs > 95%) responses compared to T5-1, respectively. We conclude that TAS2R5 pathway signaling is malleable to a more favorable therapeutic profile by agonist-receptor interactions that preserve primary signaling and minimizes desensitization.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Agonists / Agonists (Biochemistry) / Antibodies / Arrestin / Biology and Life Sciences / Bitter taste / Calcium (intracellular) / Calcium - metabolism / Calcium ions / Cell culture / Cell membranes / Desensitization / Down-regulation / Down-Regulation - drug effects / Extracellular signal-regulated kinase / G protein-coupled receptors / HEK293 Cells / Humans / Identification and classification / Influence / Internalization / Myocytes, Smooth Muscle - drug effects / Myocytes, Smooth Muscle - metabolism / Net losses / Phenotypes / Phosphorylation / Physiological aspects / Protein folding / Proteins / Receptors / Receptors, G-Protein-Coupled - agonists / Receptors, G-Protein-Coupled - genetics / Receptors, G-Protein-Coupled - metabolism / Research and Analysis Methods / Signal Transduction / Smooth muscle / Taste buds / Taste receptors / Taste Receptors, Type 2