title: Biased signaling initiated by agouti-related peptide through human melanocortin-3 and -4 receptors.
abstract: The neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), have been increasingly recognized as important regulators of energy homeostasis. The orexigenic agouti-related peptide (AgRP), initially identified as an endogenous antagonist for both neural MCRs, has been suggested to be a biased agonist of MC4R independent of its antagonizing effects. In the present study, we sought to determine the potential of AgRP to regulate the activation of intracellular kinases, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), AKT and AMP-activated protein kinase (AMPK), through neural MCRs. We showed that AgRP acted as a biased agonist in human MC3R (hMC3R), decreasing cAMP activity of constitutively active mutant (F347A) hMC3R but stimulating ERK1/2 activation in both wide type and F347A hMC3Rs. AgRP-stimulated ERK1/2 phosphorylation through MC3R was abolished by protein kinase A (PKA) inhibitor H-89 but not Rp-cAMPS, whereas AgRP-initiated ERK1/2 activation through MC4R was inhibited by phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002. Both NDP-MSH and AgRP treatment induced significant AKT phosphorylation in GT1-7 cells but not in MC3R- or MC4R-transfected HEK293T cells. The phosphorylated AMPK levels in both GT1-7 cells and HERK293T cells transfected with neural MCRs were significantly decreased upon stimulation with NDP-MSH but not with AgRP. In summary, we provided novel data for AgRP-initiated multiple intracellular signaling pathways, demonstrating biased agonism of AgRP in both neural MCRs, leading to a better understanding of neural MCR pharmacology.
authors.affiliation: Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, United States.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, United States. Electronic address: taoyaxi@auburn.edu.
authors.forename: Ya-Xiong
authors.initials: YX
authors.lastname: Tao
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D054369:Agouti-Related Protein / Q000378:metabolism*; D019943:Amino Acid Substitution; D002490:Central Nervous System / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D008024:Ligands; D020935:MAP Kinase Signaling System; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D044104:Receptor, Melanocortin, Type 3 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D044105:Receptor, Melanocortin, Type 4 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D054369:Agouti-Related Protein; D008024:Ligands; C505392:MC3R protein, human; C470072:MC4R protein, human; D010446:Peptide Fragments; D044104:Receptor, Melanocortin, Type 3; D044105:Receptor, Melanocortin, Type 4; D011994:Recombinant Proteins; C430443:agouti-related protein (86-132), human; D000242:Cyclic AMP; D051057:Proto-Oncogene Proteins c-akt; D055372:AMP-Activated Protein Kinases
keywords: Agouti-related peptide; Biased signaling; Melanocortin-3 receptor; Melanocortin-4 receptor