title: Influence of alpha-melanocyte-stimulating hormone and ultraviolet radiation on the transfer of melanosomes to keratinocytes.
abstract: The epidermal melanin unit in human skin is composed of melanocytes and keratinocytes. Melanocytes, located in the basal layer of the epidermis, manufacture melanin-loaded organelles called melanosomes. Through their dendritic processes, melanocytes distribute melanosomes to neighboring keratinocytes, where their presence confers to the skin its characteristic color and photoprotective properties. In this study, we used murine melanocytes and keratinocytes alone and in coculture to characterize the processes involved in melanosome transfer. Ultraviolet (UV) radiation induced an accumulation of melanosomes in melanocytes, whereas treatment with a-melanocyte-stimulating hormone (MSH) induced exocytosis of melanosomes accompanied by ruffling of the melanocyte membrane. We found that keratinocytes phagocytose melanosomes and latex beads equally well and that this phagocytic process was increased by exposure of keratinocytes to UV radiation or to MSH. Coculture of melanocytes and keratinocytes resulted in an increase in MSH released to the medium. Gene array analysis of MSH-treated melanocytes showed up-regulation of many genes associated with exocytosis. In our studies, we never observed cytophagocytosis of melanosome-filled processes. This result, together with the other findings, suggests that a combination of signals that increase melanosome production and release by melanocytes and that stimulate phagocytosis by keratinocytes are the most relevant mechanisms involved in skin tanning.
authors.affiliation: Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health (NIH), Bethesda, Maryland, 20892, USA.
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Virador
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Muller
authors.forename: Xufneg
authors.initials: X
authors.lastname: Wu
authors.forename: Zalfa A
authors.initials: ZA
authors.lastname: Abdel-Malek
authors.forename: Zu-Xi
authors.initials: ZX
authors.lastname: Yu
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Ferrans
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
authors.forename: John A
authors.initials: JA
authors.lastname: Hammer
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
mesh_terms: D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D018920:Coculture Techniques; D005089:Exocytosis; D020869:Gene Expression Profiling; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008863:Microspheres; D008954:Models, Biological; D020411:Oligonucleotide Array Sequence Analysis; D010587:Phagocytosis / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays; D000521:alpha-MSH / Q000494:pharmacology*
chemical_list: D000521:alpha-MSH