UV irradiation induces downregulation of bcl-2 expression in vitro and in vivo

Recently, the proto-oncogenes bcl-2 and bar have emerged as important regul ators of the apoptotic form of cell death. We examined UV irradiation-elici ted apoptosis and regulation of bcl-2 and bar expression both in vivo in hu man skin and in vitro in HeLa cells. Using flow cytometric analysis, HeLa c ells were found to undergo apoptosis at the 12-h time-point after exposure to UVB irradiation (100 mJ/cm(2)), The expression of bcl-2 mRNA was found t o decrease after a single dose of UVB radiation (doses 10-200 mJ/cm(2)). In contrast, the expression of bax mRNA was not significantly changed. When h uman skin was irradiated with a single dose of solar-simulated radiation (4 0 mJ/cm(2)), Bcl-2-positive cells were significantly reduced in the epiderm is at the 3- and 6-h time-points. Our results suggest that UV irradiation d ownregulates bcl-2 expression both in vitro at the mRNA level and in vivo a t the protein level, and that downregulation of bcl-2 constitutes a mechani sm of potential importance in UV-induced apoptosis in human epidermis.