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Differential effects of membrane sphingomyelin and cholesterol on agonist-induced bitter taste receptor T2R14 signaling

  • Feroz Ahmed Shaik
  • Prashen ChelikaniEmail author
Article
  • 197 Downloads

Abstract

Membrane lipids regulate the structure and function of G protein-coupled receptors (GPCRs). Previously we have shown that membrane cholesterol regulates the signaling of two human bitter taste receptors (T2Rs), T2R4 and T2R14. Another major plasma membrane lipid known to influence the function of membrane proteins including GPCRs is sphingomyelin. The role of sphingomyelin in T2R function is unexplored thus far. In this work, we examined the significance of sphingomyelin in T2R14 signaling. Results suggest that unavailability of membrane sphingomyelin did not affect the agonist-promoted T2R14 Ca2+ signaling in heterologous expression system and also in primary airway smooth muscle cells (HASM cells). In addition, T2R14 mediated downstream AMPK activation was also unaffected in sphingomyelin-depleted condition; however, cholesterol depletion impaired the T2R14-mediated AMPK activation. Angiotensin II type1A receptor (AT1R) expressed in HASM cells and signals through Ca2+ and AMPK was used as a control. Results suggest that similar to T2R14, membrane sphingomyelin depletion did not affect AT1R signaling. However, membrane cholesterol depletion impaired AT1R mediated Ca2+ signaling and AMPK activation. Interestingly, amino acid sequence analysis revealed the presence of putative sphingolipid binding motif in both T2R14 and AT1R suggesting that the presence of a motif alone might not be suggestive of sphingomyelin sensitivity. In conclusion, these results demonstrate that in contrast to membrane cholesterol, sphingomyelin does not affect the agonist-induced T2R14 signaling, however it may play a role in other aspects of T2R14 function.

Keywords

Bitter taste receptor (T2R) G protein-coupled receptor (GPCR) Human airway smooth muscle Sphingomyelinase Sphingolipid Cholesterol 

Abbreviations

AMPK

AMP activated protein kinase

AngII

Angiotensin II human

AT1R

Angiotensin II type1 receptor

CARC

Mirror version of CRAC motif

CRAC

Cholesterol recognition amino acid consensus

DPH

Diphenhydramine

EC50

Half-maximal effective concentration

FFA

Flufenamic acid

GPCR

G protein-coupled receptors

GRM

Metabotropic glutamate receptors

HASM

Human airway smooth muscle

IC50

Half-maximal inhibitory concentration

MßCD

Methyl-ß-cyclodextrin

p-AMPK

Phosphorylated amp activated protein kinase

SBM

Sphingolipid binding motif

SMase

Sphingomyelinase

T1Rs

Sweet and umami taste receptors

T2Rs

Bitter taste receptors

Notes

Acknowledgements

This work was supported by a grant from Natural Sciences and Engineering Research Council of Canada (RGPIN-2014-04099) and Cystic Fibrosis Canada operating Grant (491120) to PC, and University of Manitoba Graduate Fellowship to FAS.

Compliance with ethical standards

Conflict of interest

The authors declare no conflicts of interest.

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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Manitoba Chemosensory Biology Research Group, Department of Oral Biology, Children’s Hospital Research Institute of ManitobaUniversity of ManitobaWinnipegCanada
  2. 2.D319, Manitoba Chemosensory Biology Research Group and Department of Oral BiologyUniversity of ManitobaWinnipegCanada

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