Lysosomal membrane permeabilization during apoptosis--involvement of Bax?
Bcl-2 family members have long been known to control permeabilization of the mitochondrial membrane during apoptosis, but involvement of these proteins in lysosomal membrane permeabilization (LMP) was not considered until recently. The aim of this study was to investigate the mechanism underlying the release of lysosomal proteases to the cytosol seen during apoptosis, with special emphasis on the role of Bax. In human fibroblasts, exposed to the apoptosis-inducing drug staurosporine (STS), the release of the lysosomal protease cathepsin D to the cytosol was observed by immunocytochemistry. In response to STS treatment, there was a shift in Bax immunostaining from a diffuse to a punctate pattern. Confocal microscopy showed co-localization of Bax with both lysosomes and mitochondria in dying cells. Presence of Bax at the lysosomal membrane was confirmed by immuno-electron microscopy. Furthermore, when recombinant Bax was incubated with pure lysosomal fractions, Bax inserted into the lysosomal membrane and induced the release of lysosomal enzymes. Thus, we suggest that Bax is a mediator of LMP, possibly promoting the release of lysosomal enzymes to the cytosol during apoptosis.
Kågedal
Katarina
K
Division of Pathology II, Faculty of Health Sciences, Linköping University, Linköping, Sweden. katarina.kagedal@inr.liu.se
Johansson
Ann-Charlotte
AC
Johansson
Uno
U
Heimlich
Gerd
G
Roberg
Karin
K
Wang
Nancy S
NS
Jürgensmeier
Juliane M
JM
Ollinger
Karin
K
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001692:Biological Transport; D015153:Blotting, Western; D002402:Cathepsin D / Q000378:metabolism; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D007425:Intracellular Membranes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure*; D008247:Lysosomes / Q000378:metabolism*; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D010539:Permeability / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D019311:Staurosporine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D011493:Protein Kinase C; D002402:Cathepsin D; D019311:Staurosporine