Effect of C-2 ceramide on the inositol phospholipid metabolism (uptake of P-32, H-3-serine and H-3-palmitic acid) and apoptosis-related morphologicalchanges in Tetrahymena

Sphingomyelin metabolites have significant role in the regulation of many l ife processes of mammalian cells. In the present experiments the influence of phospholipid turnover and apoptosis related morphologic signs by one of this metabolite, C-2 ceramide was studied, and compared to the control, unt reated cells, in the unicellular Tetrahymena. The incorporation of phosphol ipid head group components (serine, phosphorus) show a clear time-dependenc e; while the incorporation of fatty acid component (palmitic acid) is very fast: no significant alterations were found between 5- and 60-min incubatio ns. C-2 ceramide treatment didn't alter H-3-palmitic acid incorporation int o phospholipids, however H-3-serine incorporation was mainly inhibited. The amount of total incorporated P-32 was also decreased, on the other hand th e lover concentration C-2 ceramide (10 mu M) elevated the synthesis of inos itol phospholipids. The higher concentration of C-2 ceramide (50 mu M) had inhibitory effect on the synthesis of each phospholipids examined. This mea ns that in the presence of the C-2 ceramide the synthesis, recovery and tur nover of phospholipids, participating in signal transduction, are altered. However these observations were based the uptake of labeled phospholipid pr ecursors, which gives information on the dynamics of the process, without u sing lipid mass measurements. C-2 ceramide also caused the rounding off the cells, DNA degradation and nuclear condensation. These latter observations point to morphological signs of apoptosis. The results call attention to t he role of sphingomyelin metabolites on signalization of unicellulars, to t he cross-talk between the inositol phospholipids and sphingomyelin metaboli tes, and the role of these molecules in the apoptotic processes at a low ev olutionary level. (C) 1999 Elsevier Science Inc. All rights reserved.