The BH3-only member Noxa causes apoptosis in melanoma cells by multiple pathways.

The molecular causes for resistance of melanoma to apoptosis are currently only partly understood. In the present study, we examined gene transfer and expression of the proapoptotic BH3-only protein Noxa as an alternative approach to chemotherapy and investigated the molecular mechanisms regulating Noxa-induced apoptosis. Noxa gene transfer caused dysregulation of both mitochondria and, as shown for the first time, also the endoplasmic reticulum, resulting in the accumulation of reactive oxygen species. Interestingly, expression of Noxa not only triggered the classical mitochondrial caspase cascade, but also resulted in the activation of apoptosis signal-regulating kinase1 and its downstream effectors c-Jun N-terminal kinase and p38. The activation of these kinases was abolished by antioxidants. Moreover, inhibition of the kinases by RNA interference or pharmacological inhibitors significantly attenuated Noxa-induced apoptosis. Thus, our data provide evidence for the involvement of multiple pathways in Noxa-induced apoptosis that are triggered at mitochondria and the endoplasmic reticulum, and suggest Noxa gene transfer as a complementary approach to chemotherapy.