Lysosomal membrane permeabilization and cathepsin release is a Bax/Bak-dependent, amplifying event of apoptosis in fibroblasts and monocytes.
Apoptotic stimuli have been shown to trigger lysosomal membrane permeability (LMP), leading to the release of cathepsins, which activate death signaling pathways in the cytosol. However, it is unknown whether this process is an initiating or amplifying event in apoptosis. In this study, we used fibroblasts and monocytes exposed to etoposide, ultraviolet light, FasL or deprived of interleukin-3 (IL-3) to show that LMP and the cytosolic release of cathepsins B, L and D consistently depends on Bax/Bak and components of the apoptosome. Neither Bax nor Bak resided on the lysosomes, indicating that lysosomes were not directly perforated by Bax/Bak but by effectors downstream of the apoptosome. Detailed kinetic analysis of cells lacking cathepsin B or L or treated with the cysteine protease inhibitor, E64d, revealed a delay in these cells in etoposide- and IL-3 deprivation-induced caspase-3 activation and apoptosis induction but not clonogenic survival, indicating that cathepsins amplify rather than initiate apoptosis.
Oberle
C
C
Institute of Molecular Medicine and Cell Research, Center for Biochemistry and Molecular Cell Research, Albert Ludwigs University Freiburg, Freiburg, Germany.
Huai
J
J
Reinheckel
T
T
Tacke
M
M
Rassner
M
M
Ekert
P G
PG
Buellesbach
J
J
Borner
C
C
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D053478:Apoptosomes / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism*; D002463:Cell Membrane Permeability; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D053222:Fas Ligand Protein / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D055785:Gene Knockdown Techniques; D007377:Interleukin-3 / Q000235:genetics / Q000378:metabolism; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D009000:Monocytes / Q000378:metabolism; D014466:Ultraviolet Rays; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
D000972:Antineoplastic Agents, Phytogenic; D053478:Apoptosomes; D015853:Cysteine Proteinase Inhibitors; D053222:Fas Ligand Protein; D007377:Interleukin-3; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D005047:Etoposide; D002403:Cathepsins; D053148:Caspase 3; D007930:Leucine; C108192:aloxistatin