CD 95-independent mechanisms of IL-2 deprivation-induced apoptosis in activated human lymphocytes.
Growth factor deprivation-induced apoptosis plays an important role in several cellular systems. However, knowledge of the molecular mechanisms involved are restricted to a few murine models or tumor cell lines. Therefore, we aimed studying signaling pathways leading to apoptosis in activated human peripheral T cells after IL-2 withdrawal. Lymphoblasts from patients with CD 95 (Fas/APO-1)-deficiency revealed that functional CD95 was not required to induce apoptosis after IL-2 withdrawal. Moreover, apoptosis induction in response to various cytotoxic stimuli was found to be mediated in the absence of functional CD95 but was affirmatorily influenced by IL-2 signaling. Immunoblots showed no downregulation of Bcl-2 or Bcl-xL and no upregulation of Bax, whereas decreased mitochondrial membrane potential was readily measurable 24 h after cytokine deprivation. Tetrapeptide inhibitors showed limited efficacy in preventing apoptosis whereas the caspase inhibitor zVAD-FMK potently blocked induction of apoptosis. Cleavage of different fluorogenic substrates revealed multiple caspase enzyme activities in lymphoblasts, which were not negatively affected by the fas mutation. Starting at 8 h after IL-2 withdrawal, upregulation of active caspase-3 but not of caspase-8 could be detected. Taken together, our data argue for molecular mechanisms of cytokine deprivation-induced apoptosis in activated human lymphocytes independent of CD95.
Hieronymus
T
T
Department of Medicine III, Institute for Clinical Immunology and Rheumatology, University of Erlangen-Nuremberg, 91054 Erlangen, Germany.
Blank
N
N
Gruenke
M
M
Winkler
S
S
Haas
J P
JP
Kalden
J R
JR
Lorenz
H M
HM
D017209:Apoptosis / Q000187:drug effects*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects*; D008928:Mitochondria / Q000378:metabolism; D010835:Phytohemagglutinins / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D019014:fas Receptor / Q000096:biosynthesis*
C494826:BAX protein, human; C494811:BCL2L1 protein, human; D007376:Interleukin-2; D010835:Phytohemagglutinins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D019014:fas Receptor