Inhibition of UV irradiation-induced oxidative stress and apoptotic biochemical changes in human epidermal carcinoma A431 cells by genistein

Ultraviolet (UV) light is a strong apoptotic trigger that can induce a casp ase-dependent biochemical change in cells. We previously showed that UV irr adiation can elicit caspase-3 activation and the subsequent cleavage and ac tivation of p21-activated kinase 2 (PAK2) in human epidermal carcinoma A431 cells. We report that genistein, an isoflavone compound with known inhibit ory activities to protein tyrosine kinases (PTKs) and topoisomerase-II (top o-II), can prevent UV irradiation-induced apoptotic biochemical changes (DN A fragmentation, caspase-3 activation, and cleavage/activation of PAK2) in A431 cells. Surprisingly, two typical PTK inhibitors (tyrphostin A47 and he rbimycin A) and three known topo-II inhibitors (etoposide, daunorubicin, an d novomycin) had no effect on UV irradiation-induced apoptotic biochemical changes, suggesting that the inhibitory effect of genistein is not dependen t on its property as a PTK/topo-II inhibitor. In contrast, azide, a reactiv e oxygen species (ROS) scavenger, could effectively block the UV irradiatio n-induced apoptotic cell responses. Flow cytometric analysis using the cell -permeable dye 2',7'-dichlorofluorescin diacetate as an indicator of the ge neration of ROS showed that UV irradiation caused increase of the intracell ular oxidative stress and that this increase could be abolished by azide, s uggesting that oxidative stress plays an important role in mediating the ap optotic effect of UV irradiation. Importantly, the UV irradiation-induced o xidative stress in cells could be significantly attenuated by genistein, su ggesting that impairment of ROS formation during UV irradiation is responsi ble for the antiapoptotic effect of genistein. Collectively, our results de monstrate the involvement of oxidative stress in the UV irradiation-induced caspase activation and the subsequent apoptotic biochemical changes and sh ow that genistein is a potent inhibitor for this process. (C) 2000Wiley-Lis s, Inc.