Melanin-concentrating hormone activates signaling pathways in 3T3-L1 adipocytes.
Energy homeostasis is regulated by peripheral signals, such as leptin, and by several orexigenic and anorectic neuropeptides. Recently, we reported that the orexigenic neuropeptide melanin-concentrating hormone (MCH) stimulates leptin production by rat adipocytes and that the MCH receptor (MCH-R1) is present on these cells. Here, we show that MCH-R1 is present on murine 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with 1 micromolar MCH for up to 2 h acutely downregulated MCH-R1, indicating a mechanism of ligand-induced receptor downregulation. Potential signaling pathways mediating MCH-R1 action in adipocytes were investigated. Treatment of 3T3-L1 adipocytes with 1 micromolar MCH rapidly induced a threefold and a fivefold increase in p44/42 MAPK and pp70 S6 kinase activities, respectively. In addition, 3T3-L1 adipocytes transiently transfected with a murine leptin-luciferase promoter construct showed a fourfold and a sixfold increase in leptin promoter-reporter gene expression at 1 h and 4 h, respectively, in response to MCH. Activity decreased to basal levels at 8 h. Furthermore, MCH-stimulated leptin promoter-driven luciferase activity was diminished in the presence of the MAP/ERK kinase inhibitor PD-98059 and in the presence of rapamycin, an inhibitor of pp70 S6 kinase activation. These results provide further evidence for a functional MCH signaling pathway in adipocytes.
Bradley
Richard L
RL
Research Division, Joslin Diabetes Center and the Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.
Mansfield
Julia P R
JP
Maratos-Flier
Eleftheria
E
Cheatham
Bentley
B
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000502:physiology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D015536:Down-Regulation; D004983:Ethanolamines / Q000494:pharmacology; D007028:Hypothalamic Hormones / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D020738:Leptin / Q000235:genetics / Q000494:pharmacology; D008156:Luciferases / Q000378:metabolism; D008543:Melanins / Q000494:pharmacology*; D051379:Mice; D010907:Pituitary Hormones / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D011979:Receptors, Pituitary Hormone / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*
D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; D007028:Hypothalamic Hormones; D007328:Insulin; D020738:Leptin; D008543:Melanins; D010907:Pituitary Hormones; D011979:Receptors, Pituitary Hormone; C092274:melanin-concentrating hormone receptor; C057368:BRL 37344; C019463:melanin-concentrating hormone; D008156:Luciferases