THE EFFECT OF MELITTIN ON PROLIFERATION AND DEATH OF THYMOCYTES

The effect of melittin, an activator of phospholipase A(2), on prolife ration and death of rat thymocytes in a broad concentration range was studied, Cell proliferation was estimated by the accumulation of colch icin metaphases, necrotic death was determined from lysis and staining of cells with trypan blue, and apoptosis was assessed from the type o f DNA fragmentation, the amount of fragmented DNA, and the percentage of cells with subdiploid DNA, It was shown that low melittin concentra tions (below 5 mu g/ml) stimulate thymocyte proliferation. At high mel ittin concentrations, thymocytes die by the primary necrosis type, Thr oughout the concentration range studied, melittin does not produce apo ptosis in thymocytes. Conversely, high melittin concentrations even in hibit thymocyte apoptosis in the control and after irradiation, An inh ibitor of RNA synthesis actinomycin D does not affect thymocyte death in the presence of melittin, It is concluded that the activation of ph ospholipase A(2) can induce necrosis but not apoptosis and thus is not a necessary step in the signaling cascade that initiates apoptosis in thymocytes. (C) 1997 Federation of European Biochemical Societies.