HEAT-SHOCK INDUCTION OF APOPTOSIS IN PROMASTIGOTES OF THE UNICELLULARORGANISM LEISHMANIA (LEISHMANIA) AMAZONENSIS

Apoptosis and/or programmed cell death have been described in examples ranging from fungi to man as gene-regulated processes with roles in c ell and tissue physiopathology. These processes require the operation of an intercellular communicating network able to deliver alternative signals for cells with different fates and is thus considered a prerog ative of multicellular organisms. Promastigotes from Leishmania (Leish mania) amazonensis, when shifted from their optimal in vitro growth te mperature (22 degrees C) to the temperature of the mammalian host (37 degrees C), die by a calcium-modulated mechanism. More parasites die i n the presence of this ion than in its absence, as detected by a color imetric assay based on the activity of mitochondrial and cytoplasmic d ehydrogenases which measures cell death, independently of the process by which it occurs. A heat shock, unable to induce detectable parasite death (34 degrees C for 1 h), is able to significantly raise the conc entration of intracellular free calcium in these cells. Heat-shocked p arasites present ultrastructural and molecular features characteristic of cells dying by apoptosis. Morphological changes, observed only in the presence of calcium, are mainly nuclear. Cytoplasmic organelles ar e preserved. Heat shock is also able to induce DNA cleavage into an ol igonucleosomal ladder detected in agarose gels by ethidium bromide sta ining and autoradiography of [alpha(32)P]ddATP-labeled fragments. Thes e results indicate that death by apoptosis is not exclusive of multi-c ellular organisms. (C) 1996 Wiley-Liss, Inc.