Two pathways of apoptosis induced with all-trans retinoic acid and etoposide in the myeloid cell line P39

P3B/Tsugane is a myelomonocytoid cell line derived from a patient with myelodysplastic syndrome (MDS), The cells readily undergo apoptosis in response to various agents, and the cell line has been suggested as a useful model to study apoptosis in MDS, The aims of the present study were to assess differentiation and apoptosis induced with all-trans retinoic acid (ATRA) and etoposide, to characterize the mode of apoptosis in these two model systems, and to assess the influence of granulocyte colony-stimulating factor (G-CSF), which in combination with erythropoietin has been shown to inhibit apoptosis in MDS, ATRA induced differentiation and apoptosis in a concentration- and time-dependent manner. Differentiated cells were partially rescued (by 50%) from apoptosis with G-CSF, Etoposide induced apoptosis in a concentration- and time-dependent manner, but no signs of preceding maturation or G-CSF rescue were detected. ATRA- and etoposide-induced apoptosis were both mediated through the caspase pathway and were partially blocked with the general caspase inhibitor zVAD-fmk, Simultaneous treatment with G-CSP and zVAD-fmk additively blocked ATRA-induced apoptosis, However, the two pathways differed in terms of substrate cleavage during apoptosis, ATRA-induced apoptosis caused actin cleavage, which was not affected by G-CSF, and Bcl-2 downregulation, Etoposide induced a caspase-dependent cleavage of Bcl-2, while actin remained intact. The Fas system did not seem to play a major role in any of these apoptotic pathways, Our results may provide new tools to study the mechanisms of apoptosis in MDS. (C) 1999 International Society for Experimental Hematology. Published by Elsevier Science Inc.