Phosphorylated P53 on serine 15, occurring as a response to DNA damage was previously shown to integrate into lysosomal membranes leading to their permeabilization (Johansson et al., 2010). ER stress and autophagic processes are known to lead to acidification of lysosomes (Kouroku et al., 2007). However, the present data do not clearly indicate that lysosomal acidification is the reason for lysosomal

permeabilization, as the decrease in lysosomal mass (permeabilization) preceded acidification. Nevertheless, the data shown in Fig. 3F indicate, that autophagic signalling does occur in endothelial cells in response to Cd exposure. Interestingly, we could previously show that cigarette smoke extract (cigarette smoke is the most important source for Cd uptake by non-occupationally exposed humans)

also induces autophagy. It may be speculated that Roxadustat price Cd is the autophagy-inducing agent in cigarette smoke (Csordas PR-171 research buy et al., 2011). Lysosomes are highly redox sensitive organelles, and some previous studies have provided data that Cd induces the formation of reactive oxygen species (ROS) and oxidative stress (Pathak and Khandelwal, 2008 and Yang et al., 2008). However, in our own previous study the occurrence of oxidative stress in response to Cd treatment of endothelial cells was ruled out as a mechanism in Cd-induced cell death (Messner et al., 2009). Mitochondria are known to be interconnected to lysosomes, via the mitochondrial–lysosomal axis. In essence, mitochondrial permeabilization can cause lysosomal permeabilization, via ROS, and lysosomes can cause mitochondrial permeabilization via cathepsins (Jaattela, 2004, Johansson

et al., 2010 and Repnik et al., 2012). As above, as the occurrence of ROS in Cd-induced cell death was ruled out, the present data suggest that it is rather that Cd-induced lysosomal permeabilization causes mitochondrial permeabilization, than the other way round. Finally, Ca2+ is known to be a stimulator of lysosomal permeabilization (Kroemer and Jaattela, 2005). Sources for a cytosolic increase in Ca2+ are Ixazomib supplier the extracellular space, mitochondria, and the ER. Hence, the involvement of extracellular Ca2+, the ER, and mitochondria, all central elements in Ca2+ signalling cannot be excluded as players in Cd-induced lysosomal permeabilization and necrosis. In summary, the data provided herein show that Cd-induced cell death signalling, in the rather terminal stages, still 24 h prior to plasma membrane rupture, leads to acidification and permeabilization of lysosomes. The disintegration of lysosomes, indicated by the reduction in lysosomal dye signal intensity and the increase of DNAse activity in the cytosol of Cd-treated cells leads to proteolysis, lipidolysis and digestion of nucleic acids – consequently to the deterioration of physiological functions, ultimately resulting in cellular necrosis (Fig. 4). The site of the inhibitory activity of BCL-XL could not definitely be demonstrated.