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

Abstract Recently, the proto-oncogenes bcl-2 and bax have emerged as important regulators of the apoptotic form of cell death. We examined UV irradiation-elicited apoptosis and regulation of bcl-2 and bax expression both in vivo in human skin and in vitro in HeLa cells. Using flow cytometric analysis, HeLa cells were found to undergo apoptosis at the 12-h time-point after exposure to UVB irradiation (100 mJ/cm²). The expression of bcl-2 mRNA was found to decrease after a single dose of UVB radiation (doses 10–200 mJ/ cm²). In contrast, the expression of bax mRNA was not significantly changed. When human skin was irradiated with a single dose of solar-simulated radiation (40 mJ/cm²), Bcl-2-positive cells were significantly reduced in the epidermis at the 3- and 6-h time-points. Our results suggest that UV irradiation downregulates bcl-2 expression both in vitro at the mRNA level and in vivo at the protein level, and that downregulation of bcl-2 constitutes a mechanism of potential importance in UV-induced apoptosis in human epidermis.