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Temporal Selectivity of Melanocortin‐4 Receptor Agonist to Modulate Signaling by Increased Intracellular cAMP
Author(s) -
Cooney Kimberly,
Molden Brent,
West Kirk,
Baldini Giulia
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.728.23
Subject(s) - agonist , receptor , melanocortin 4 receptor , chemistry , desensitization (medicine) , endocrinology , functional selectivity , internalization , förster resonance energy transfer , intracellular , g protein coupled receptor , medicine , endogenous agonist , homologous desensitization , microbiology and biotechnology , melanocortin , biophysics , biology , biochemistry , fluorescence , physics , quantum mechanics , dopamine receptor d1
Melanocortin‐4 Receptor (MC4R) is a G‐protein coupled receptor expressed in the brain where it functions to regulate food intake and energy expenditure. MC4R signals in response to its natural agonist, α‐MSH, by increasing intracellular cAMP. It is not known whether synthetic MC4R agonists exhibit functional selectivity to modulate the cAMP signal. Effects by α‐MSH and two synthetic agonists, Melanotan II (MT‐II) and THIQ, were monitored using Neuro‐2A cells expressing both endogenous MC4R and exogenous tagged HA‐MC4R‐GFP, which can be visualized directly by fluorescence microscopy. By using Fluorescence Resonance Energy Transfer (FRET) we determined that α‐MSH induces a cAMP signal that disappears rapidly, within 15 min after agonist withdrawal. Conversely, MT‐II and THIQ induce a more prolonged cAMP signal, lasting for at least 40 min after agonist withdrawal. Internalization rate of ligand‐free MC4R and MC4R in a complex with a‐MSH and MT‐II, monitored by Fluorescence Recovery after Photobleaching (FRAP) occurred with the same half‐life of ~2.5 min. Together, these data indicate that MT‐II can induce a cAMP signal even after being internalized. Exposure to a‐MSH for 4 hours increased the distribution of MC4R to the intracellular localization more efficiently than MT‐II and THIQ, however desensitization of the receptor was the same for all agonists. We conclude that MC4R agonists have temporal selectivity to modulate the duration of the cAMP signal after agonist withdrawal, but not to change the desensitization properties of the receptor. NIH Grants R01‐DK080424 (to G. B.) and Intramural Funding Support from the UAMS College of Medicine Research Council