Control of survival of proliferating L1210 cells by soluble guanylate cyclase and p44/42 mitogen-activated protein kinase modulators

Intracellular signaling pathways involved in the survival of proliferating L1210 leukemia cells were investigated by using specific modulators. Among the various inhibitors tested, only 1H-[1,2,4]oxadiazole [4,3-a]quinoxalin- 1-one (ODQ), a soluble guanylate cyclase (sGC) inhibitor, was found to indu ce a marked increase in caspase activity, which was associated with a loss of cell viability and a reduction in cGMP content. ODQ also provoked the pr ocessing of caspases-3 and -9, release of cytochrome c and, as early events , reduction of Bcl-2 content and dephosphorylation of Bad at Ser 112. Furth ermore, YC-1, an sGC activator, and 8-Br-cGMP, a cell-permeant analogue of cGMP, exerted some protection against various apoptotic stimuli, such as se rum deprivation or spermine accumulation. Although PD98059 (2'-amino-3'-met hoxyflavone), an inhibitor of the p44/42 mitogen-activated protein kinase ( MAPK) pathway, did not increase basal caspase activity, and ODQ did not aff ect p44/42 MAPK phosphorylation significantly, phorbol myristate acetate st imulated p44/42 MAPK and reduced caspase activation induced by ODQ, serum d eprivation, and spermine in a p44/42-dependent manner. SB203580 (4-(4-fluor ophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl) 1H-imidazole), a p38 MAPK inhibitor, also partially protected against ODQ-induced apoptosis by incre asing p44/42 MAPK phosphorylation. In conclusion, these results suggest tha t sGC may be relevant both for survival of L1210 cells under basal growing conditions and for protection against various apoptotic stimuli. p44/42 MAP K activation may also confer some protection from apoptosis, but apparently through a pathway largely independent of cGMP. (C) 2001 Elsevier Science I nc. All rights reserved.