The tyrosine kinase lck is required for CD95-independent caspase-8 activation and apoptosis in response to ionizing radiation.
Induction of apoptosis is a hallmark of cytostatic drug and radiation-induced cell death in human lymphocytes and lymphoma cells. However, the mechanisms leading to apoptosis are not well understood. We provide evidence that ionizing radiation induces a rapid activation of caspase-8 (FLICE) followed by apoptosis independently of CD95 ligand/receptor interaction. The radiation induced cleavage pattern of procaspase-8 into mature caspase-8 resembled that following CD95 crosslinking and resulted in cleavage of the proapoptotic substrate BID. Overexpression of dominant-negative caspase-8 interfered with radiation-induced apoptosis. Caspase-8 activation by ionizing radiation was not observed in cells genetically defective for the Src-like tyrosine kinase Lck. Cells lacking Lck also displayed a marked resistance towards apoptosis induction upon ionizing radiation. After retransfection of Lck, caspase-8 activation and the capability to undergo apoptosis in response to ionizing radiation was restored. We conclude that radiation activates caspase-8 via an Lck-controlled pathway independently of CD95 ligand expression. This is a novel signaling event required for radiation induced apoptosis in T lymphoma cells.
Belka
C
C
Department of Radiation Oncology, University of Tuebingen (Germany), Hoppe Seyler Str. 3, 72076 Tuebingen, Germany.
Marini
P
P
Lepple-Wienhues
A
A
Budach
W
W
Jekle
A
A
Los
M
M
Lang
F
F
Schulze-Osthoff
K
K
Gulbins
E
E
Bamberg
M
M
D000906:Antibodies; D017209:Apoptosis / Q000528:radiation effects*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000528:radiation effects; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D053222:Fas Ligand Protein; D005799:Genes, Dominant / Q000235:genetics; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011499:Protein Processing, Post-Translational / Q000528:radiation effects; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D011839:Radiation, Ionizing; D015398:Signal Transduction / Q000528:radiation effects*; D012995:Solubility; D014162:Transfection; D019014:fas Receptor / Q000378:metabolism*
D000906:Antibodies; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D004792:Enzyme Precursors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D019014:fas Receptor; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases