Low UVA doses activate the transcription factor NFAT in human fibroblasts by a calcium-calcineurin pathway.
UVA radiation induces an inflammatory response as observed in erythema, and the cytokine genes involved in this response are under the control of the transcription factor NFAT (nuclear factor of activated T lymphocytes). The effects of UVA on NFAT DNA binding activity were investigated in cultured human fibroblasts. A dose-dependent increase was observed within the range of 0.6-4.5 J/cm2 UVA. Beyond this value, the activity decreased and a value of 60% of control was found at 13.5 J/cm2. The enhancement of NFAT activity was transient and peaked 45 min after irradiation. Furthermore, immunoblot analysis demonstrated a nuclear translocation of NFAT under low UVA doses. Concomitantly, as assessed by the fluorescent probe Fluo3, UVA induced an increase in intracellular free calcium, with a maximum increase found at 9 J/cm2. The UVA-induced activation of NFAT was prevented by the intracellular calcium trapping drug BAPTA, whereas the extracellular calcium chelator EGTA had no significant effect. In addition, the calcineurin inhibitors cyclosporin A and FK506 both prevented the UVA-induced NFAT activation. Furthermore, the antioxidant vitamin E prevented the UVA-induced increase in both intracellular free calcium and NFAT binding activity. Finally, the cytotoxicity of UVA was enhanced in the presence of the inhibitors cyclosporin and FK506, suggesting that the activation of NFAT might play a protective role after the UVA-induced oxidative stress. These results demonstrate that UVA activates the calcium-calcineurin signaling pathway of NFAT activation, that the calcium ions are mainly released from intracellular stores, and that the increase in calcium is, at least partially, due to the oxidative stress generated under UVA. Because NFAT regulates several genes implicated in the inflammatory response, the enhancement of NFAT activity by low UVA doses might be interpreted in view of the proinflammatory action of solar radiation.
Mazière
Cécile
C
Laboratoire de Biochimie EA 2087 and INSERM-ERI 12, CHU Amiens, Hôpital Nord, Place Victor Pauchet, 80054 Amiens Cedex 1, France. maziere.cecile@chu-amiens.fr
Morlière
Patrice
P
Louandre
Christophe
C
Conte
Marie-Alix
MA
Gomilla
Cathy
C
Santus
René
R
Antonicelli
Franck
F
Hornebeck
William
W
Mazière
Jean-Claude
JC
D000975:Antioxidants / Q000494:pharmacology; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D004247:DNA / Q000378:metabolism / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D050778:NFATC Transcription Factors / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects*; D016559:Tacrolimus / Q000494:pharmacology; D014466:Ultraviolet Rays; D014810:Vitamin E / Q000494:pharmacology
D000975:Antioxidants; D065095:Calcineurin Inhibitors; D050778:NFATC Transcription Factors; D014810:Vitamin E; D004533:Egtazic Acid; D016572:Cyclosporine; D004247:DNA; D019703:Calcineurin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D016559:Tacrolimus