title: Agouti signaling protein inhibits melanogenesis and the response of human melanocytes to alpha-melanotropin.
abstract: In mouse follicular melanocytes, the switch between eumelanin and pheomelanin synthesis is regulated by the extension locus, which encodes the melanocortin-1 receptor (MC1R) and the agouti locus, which encodes a novel paracrine-signaling molecule that inhibits binding of melanocortins to the MC1R. Human melanocytes express the MC1R and respond to melanotropins with increased proliferation and eumelanogenesis, but a potential role for the human homolog of agouti-signaling protein, ASIP, in human pigmentation has not been investigated. Here we report that ASIP blocked the binding of alpha-melanocyte-stimulating hormone (alpha-MSH) to the MC1R and inhibited the effects of alpha-MSH on human melanocytes. Treatment of human melanocytes with 1 nM-10 nM recombinant mouse or human ASIP blocked the stimulatory effects of alpha-MSH on cAMP accumulation, tyrosinase activity, and cell proliferation. In the absence of exogenous alpha-MSH, ASIP inhibited basal levels of tyrosinase activity and cell proliferation and reduced the level of immunoreactive tyrosinase-related protein-1 (TRP-1) without significantly altering the level of immunoreactive tyrosinase. In addition, ASIP blocked the stimulatory effects of forskolin or dibutyryl cAMP, agents that act downstream from the MC1R, on tyrosinase activity and cell proliferation. These results demonstrate that the functional relationship between the agouti and MC1R gene products is similar in mice and humans and suggest a potential physiologic role for ASIP in regulation of human pigmentation.
authors.affiliation: POLA Laboratories, Yokohama, Japan.
authors.forename: I
authors.initials: I
authors.lastname: Suzuki
authors.forename: A
authors.initials: A
authors.lastname: Tada
authors.forename: M M
authors.initials: MM
authors.lastname: Ollmann
authors.forename: G S
authors.initials: GS
authors.lastname: Barsh
authors.forename: S
authors.initials: S
authors.lastname: Im
authors.forename: M L
authors.initials: ML
authors.lastname: Lamoreux
authors.forename: V J
authors.initials: VJ
authors.lastname: Hearing
authors.forename: J J
authors.initials: JJ
authors.lastname: Nordlund
authors.forename: Z A
authors.initials: ZA
authors.lastname: Abdel-Malek
mesh_terms: D054366:Agouti Signaling Protein; D000818:Animals; D015153:Blotting, Western; D003994:Bucladesine / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D008543:Melanins / Q000378:metabolism*; D008544:Melanocytes / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D008562:Membrane Glycoproteins; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases; D010858:Pigmentation / Q000502:physiology; D011506:Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D011979:Receptors, Pituitary Hormone / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D000521:alpha-MSH / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D054366:Agouti Signaling Protein; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D008543:Melanins; D008562:Membrane Glycoproteins; D008934:Mitogens; D011506:Proteins; D011979:Receptors, Pituitary Hormone; D011994:Recombinant Proteins; D005576:Colforsin; D000521:alpha-MSH; D003994:Bucladesine; C029446:MSH receptor; D000242:Cyclic AMP; D010088:Oxidoreductases; C489799:TYRP1 protein, human; C079621:Tyrp1 protein, mouse; C064056:tyrosinase-related protein-1; D014442:Monophenol Monooxygenase