title: Characterization of keratinocyte differentiation induced by ascorbic acid: protein kinase C involvement and vitamin C homeostasis.
abstract: Epidermal keratinocytes undergo differentiation in response to several stimuli to form the cornified envelope, a structure that contributes to the barrier function of skin. Although differentiation has been extensively analyzed, the precise role of vitamin C during this process is still not defined. Ascorbic acid, besides acting as a radical scavenger, has been shown to promote mesenchymal differentiation. In this study, we found that keratinocytes grown in ascorbate-supplemented medium developed a differentiated phenotype, as demonstrated by enhanced expression of marker genes and increase in cornified envelope content. The pro-differentiating effects of ascorbate were mediated by the protein-kinase-C-dependent induction of activating protein 1 DNA binding activity; indeed, down-modulation of protein kinase C activity abolished differentiation triggered by ascorbic acid. Although vitamin C appeared to regulate the same signaling pathway modulated by calcium, a classical in vitro inducer of epidermal differentiation, nonetheless terminally differentiated keratinocytes exhibited different ascorbate homeostasis and cellular antioxidant status. Indeed, we found that, unlike calcium, differentiation promoted by ascorbate was accompanied by (i) an enhanced ascorbate transport, due to overexpression of specific transporters, (ii) a great efficiency of dehydroascorbate uptake, and (iii) an increase in glutathione content with respect to proliferating cells. Ascorbic acid may be useful to promote epidermal differentiation, avoiding depletion of hydrophilic antioxidant stores.
authors.affiliation: Department of Experimental Medicine and Biochemical Sciences, University of Rome Tor Vergata, Rome, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Savini
authors.forename: Maria Valeria
authors.initials: MV
authors.lastname: Catani
authors.forename: Antonello
authors.initials: A
authors.lastname: Rossi
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Duranti
authors.forename: Gerry
authors.initials: G
authors.lastname: Melino
authors.forename: Luciana
authors.initials: L
authors.lastname: Avigliano
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism* / Q000494:pharmacology*; D001692:Biological Transport / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006706:Homeostasis; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000502:physiology
chemical_list: D018808:Transcription Factor AP-1; D011493:Protein Kinase C; D001205:Ascorbic Acid