Characterization of T2Rs in the vasculature and elucidation of T2R4 desensitization mechanism
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Date
2014, 2015
Authors
Upadhyaya, Jasbir
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Humans can taste many compounds but are able to distinguish between five basic tastes, bitter, sweet, umami, sour and salt. Bitter taste, which is mediated by 25 bitter taste receptors (T2Rs) in humans, acts as a central warning signal against the ingestion of toxic compounds. In addition to their expression in the oral cavity, T2Rs are expressed in various extra-oral tissues, suggesting that they have additional functions apart from sensing taste. The recent finding that T2Rs, upon activation with bitter tastants, cause muscle relaxation and bronchodilation of pre-contracted airway smooth muscle, has been a topic of consideration. The bronchodilatory role of T2Rs, which was three fold greater than that elicited by currently used beta-adrenergic receptor agonists, has implicated them as potential therapeutic targets for the treatment of asthma. In view of the importance of T2R function in extra-oral tissues, it is of fundamental importance to determine their physiological role in extra-oral regions like the vascular tissues, and understand how T2R signal is regulated.
In this study, two representative bitter taste receptors, T2R1 and T2R4, were selected to elucidate the function and signal regulation of T2Rs. The expression of T2Rs was characterized in pulmonary artery smooth muscle cells, and studies were pursued to explore the effects of dextromethorphan (DXM) on the pulmonary artery. DXM caused vasoconstriction in pulmonary arterial cells by activating endogenous T2R1. The structure-function role of the C-terminus of T2R4 receptor was characterized by site-directed mutagenesis. A conserved KLK motif was identified in the C-terminus and many residues involved in cell surface targeting and function of T2R4 were revealed. A constitutively active mutant (CAM) was also discovered within the T2R4 C-terminus. To identify the regulatory proteins involved in T2R4 desensitization, a molecular and pharmacological approach was used. The kinases involved in this process were identified by performing either a knockdown or by using activators and inhibitors. The potential residues of T2R4 involved in desensitization were assessed for function. In addition, the internalization status of few T2Rs was determined by using different bitter compounds. This study provides novel insights into the function and desensitization of T2Rs and reports a pharmacochaperone activity for quinine.
Description
Keywords
GPCRs, Desensitization
Citation
Dextromethorphan mediated bitter taste receptor activation in the pulmonary circuit causes vasoconstriction
The structure-function role of C-terminus in human bitter taste receptor T2R4 signalling
The structure-function role of C-terminus in human bitter taste receptor T2R4 signalling