title: Evidence for glycosylation as a regulator of the pigmentary system: key roles of sialyl(α2-6)gal/GalNAc-terminated glycans in melanin synthesis and transfer.
abstract: The major regulators of melanogenesis are glycoproteins, however no role for glycosylation in the pathway has yet been described. We stained skin biopsies and melanocyte-keratinocyte co-cultures with a panel of 20 lectins as oligosaccharide markers. Notably, the Elderberry Bark Lectin (EBL/SNA) stained melanocytes in both systems. EBL binds the sequence Neu5Ac(α(2-6)Gal/GalNAc)- at the termini of some oligosaccharide antennae. We used inhibitors of synthesis and/or binding of this sequence to assess effects on pigmentation.
  
  
  METHODS
  Cell culture, lectin histochemistry, siRNA transfection, and assays for dopa oxidase and melanin were carried out by standard techniques.
  
  
  RESULTS
  6'-sialyllactose, a short homolog of the sequence in question, anti-sialyltransferase 6 (ST6) siRNA, and cytidine, a sialyltransferase (ST) inhibitor, each inhibited EBL binding, melanogenesis and melanosome transfer. Unexpectedly, 3'-sialyllactose and siRNA for ST3, chosen as a negative controls, also inhibited these processes. Though strong inhibitors of melanization, none of the agents affected tyrosinase/dopa oxidase activity, indicating previously unrecognized post-tyrosinase regulation of melanization.
  
  
  CONCLUSIONS
  We report for the first time that Neu5Ac (α(2-6)Gal/GalNAc)- and possibly Neu5Ac(α(2-3)Gal/GalNAc)-terminated oligosaccharides play multiple roles in melanin synthesis and transfer.
authors.affiliation: Analytical Sciences, The Amway Corporation, Ada, MI, USA.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Diwakar
authors.forename: Vincent
authors.initials: V
authors.lastname: Klump
authors.forename: Rossitza
authors.initials: R
authors.lastname: Lazova
authors.forename: John
authors.initials: J
authors.lastname: Pawelek
mesh_terms: D002240:Carbohydrate Sequence; D018920:Coculture Techniques; D003562:Cytidine / Q000494:pharmacology; D005688:Galactosamine / Q000378:metabolism*; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000378:metabolism; D010858:Pigmentation / Q000187:drug effects; D011134:Polysaccharides / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase
chemical_list: D008543:Melanins; D011134:Polysaccharides; D034741:RNA, Small Interfering; D003562:Cytidine; D005688:Galactosamine; D014442:Monophenol Monooxygenase; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase; C000722087:ST3GAL1 protein, human