title: Induction of gene expression via activator protein-1 in the ascorbate protection against UV-induced damage.
abstract: UV irradiation is a major insult to the skin. We have shown previously that exogenous vitamin C (ascorbate) accumulates in HaCaT keratinocytes, thus conferring the ability to prevent radical formation and cell death elicited by UV-B. Here, we have investigated the potential mechanisms accounting for the cytoprotective effects exerted by this antioxidant. Using a cDNA microarray hybridization, we identified several genes whose expression was up-regulated by ascorbate. We focused on the fra-1 gene, a member of the Fos family of transcription factors that down-regulates activator protein-1 (AP-1) target genes. Both in HaCaT and in normal human epidermal keratinocytes, we found Fra-1 mRNA induction as early as 2 h after ascorbate loading. Electrophoretic mobility-shift assay and antibody supershift analysis revealed that ascorbate modulates AP-1 DNA-binding activity and that Fra-1 is in AP-1 complexes in treated cells. Furthermore, transient-transfection studies, using an AP-1 reporter construct, showed that ascorbate was able to inhibit both basal and UV-B-induced AP-1-dependent transcription. Ascorbate also modulates UV-B-induced AP-1 activity by preventing the phosphorylation and activation of the upstream c-Jun N-terminal kinase (JNK), thus inhibiting phosphorylation of the endogenous c-Jun protein. These data suggest that ascorbate mediates cellular responses aimed at counteracting UV-mediated cell damage and cell death by interfering at multiple levels with the activity of the JNK/AP-1 pathway and modulating the expression of AP-1-regulated genes.
authors.affiliation: Biochemistry Laboratory, IDI-IRCCS, c/o Department of Experimental Medicine & Biochemical Sciences, University of Rome Tor Vergata, Via di Tor Vergata 135, 00133 Rome, Italy.
authors.forename: M V
authors.initials: MV
authors.lastname: Catani
authors.forename: A
authors.initials: A
authors.lastname: Rossi
authors.forename: A
authors.initials: A
authors.lastname: Costanzo
authors.forename: S
authors.initials: S
authors.lastname: Sabatini
authors.forename: M
authors.initials: M
authors.lastname: Levrero
authors.forename: G
authors.initials: G
authors.lastname: Melino
authors.forename: L
authors.initials: L
authors.lastname: Avigliano
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000528:radiation effects*; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D011837:Radiation-Protective Agents; D018808:Transcription Factor AP-1; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D001205:Ascorbic Acid