Expression of mitochondrial Apo2.7 molecules and caspase-3 activation in human lymphocytes treated with the ribosome-inhibiting mistletoe lectins and the cell membrane permeabilizing viscotoxins

Abstract

Background: It is unclear whether expression of newly described mitochondrial Apo2.7 molecules (7A6 antigen) is specific for apoptosis or may also occur in necrosis. Methods: We incubated human lymphocytes with the apoptosis-inducing mistletoe lectin (ML) I and the cell membrane- permeabilizing viscotoxins (VT), and measured cell death-associated changes by flow cytometry. Results: In ML I-treated lymphocytes, Apo2.7 expression and caspase-3 activation was recognized within 24 h. In VT-treated cells, we observed an Apo2.7 expression with low fluorescence level, while active caspase-3 and DNA fragments (TUNEL) were not detected within 24 h. In these cells, caspase-3 activation was recognized 48 h later. As a major subset of ML-treated cells expressing Apo2.7 molecules did not activated caspase-3, while all caspase-3+ cells did express Apo2.7, one may suggest that the caspase pathway is activated secondarily to mitochondrial events. Conclusions: Expression of Apo2.7 is sensitive marker of cell death but may not be specific for apoptosis alone as it can be detected also in cells treated with cell membrane-permeabilizing toxins. On the other hand, this expression may be the consequence of an induction of distinct 'death signals' resulting in apoptosis later on.