ZINC AND DNA FRAGMENTATION IN KERATINOCYTE APOPTOSIS - ITS INHIBITORYEFFECT IN UVB IRRADIATED-CELLS

Zinc has been shown to have antioxidant properties and to exhibit inhi bitory effects on apoptosis. In this work we investigated the effect o f zinc on DNA integrity and on apoptosis of HaCaT keratinocytes. Cells were submitted to zinc deprivation by a diffusible zinc chelator, ,N, N',N'-tetrakis(2-pyridylmethyl)ethylenediamine) (TPEN) or supplied wit h zinc chloride and submitted to UVB radiation. After cell exposure to TPEN for 2 h, strand breaks significantly impaired DNA resistance to alkaline denaturation. DNA strand breaks induced by a 6 h TPEN applica tion were significantly prevented if zinc chloride was supplied togeth er with the chelator. TPEN also generated, after 4-6 h Of application, cytoplasmic histone-associated DNA fragments (mononucleosomes and oli gonucleosomes), features of cell death by apoptosis. Moreover, UVB irr adiation led to early DNA strand breaks and to an increase in cytoplas mic nucleosomes which was maximum 10 h after irradiation. These effect s were prevented by the supply of zinc chloride (0.1 mM) in the cultur e medium. These results suggest that zinc ions interfere with the apop tosis process at an early stage, by decreasing DNA damage able to trig ger apoptosis.