CLEAVED INTRACELLULAR PLASMINOGEN-ACTIVATOR INHIBITOR-2 IN HUMAN MYELOLEUKAEMIA CELLS IS A MARKER OF APOPTOSIS

The proteolytic modification of plasminogen activator inhibitor 2 (PAI-2) was studied during apoptosis in the human promyelocytic leukaemic NB4 cell line during treatment with the phosphatase inhibitors okadaic acid and calyculin A as well as the protein synthesis inhibitor cycloheximide. The apoptic type of cell death was ascertained by morphological and biochemical criteria. in cell homogenates PAI-2 was probed by [I-125]urokinase plasminogen activator (uPA) and detected as a sodium dodecy] sulphate-stable M(T) 80,000 complex after reducing sodium dodecy] sulphate-polyacrylamide gel electrophoresis and autoradiography. During apoptosis a smaller (M(r) 70,000) uPA-PAI-2 complex was consistently detected. The modification was in the PAI-2 moiety, as the [I-125]uPA tracer could be extracted in its intact form from the complex. Thus the cleaved PAI-2 isoform is a biochemical marker of apoptosis in the promyelocytic NB4 cell line. The modified PAI-2 isoform was also detected in homogenates made from purified human mononuclear leukaemic cells aspirated from the bone marrow of patients suffering From acute and chronic myeloid leukaemia.