A Method to Monitor Lysosomal Membrane Permeabilization by Immunocytochemistry

Programmed cell death involving lysosomal membrane permeabilization (LMP) is a common phenomenon--more the rule than the exception under various cytotoxic stimuli and stressful cellular conditions. The protocol presented here is based on immunocytochemical staining of cathepsin B or L to visualize translocation from the lysosomal lumen to the cytosol. In healthy cells, cathepsins appear in localized punctate structures representing intact lysosomes, whereas LMP results in a diffuse staining pattern throughout the cytoplasm. LMP can be triggered upstream, downstream, or independently of the classical apoptotic death pathway involving mitochondrial outer membrane permeabilization (MOMP). Co-staining with antibodies recognizing the active form of Bax allows investigation of the order of events between LMP and MOMP in death signaling.