Figure 4

p38 MAPK is activated and promotes survival in U937 cells. (a, b) U937 cells were pretreated with SB203580 (10 μM), inhibitor of p38 MAPK or with PD98059 (10 μM), inhibitor of ERK MAPK for 30 min and then exposed or not to OUA (100 nM) for 24h. (a) U937 cells were fixed and stained with propidium iodide; subG1 events in the cell cycle were evaluated under cytofluorimetry. (b) A portion of unfixed cells were counted in a hemocytometer as excluding and not excluding trypan blue. Viability was obtained by calculating live (trypan blue-excluding) cells as a percentage of all counted cells. The reported values represent the means and the error bars the SD of the percentage of live cells (trypan blue-excluding) or subG1 events of five independent experiments. Assessment of cell survival was investigated and statistically significant differences (P<0.01) were found between the data obtained using OUA and (SB+OUA). c) Western blot analysis of activated p38 in the lysates of U937 cells either pretreated or not with KBR (10 μM) and then exposed or not to ouabain 100 nM for the time indicated. Blotted proteins were probed with anti-phospho-p38 and then with anti-p38 antibodies, each followed by peroxidase-conjugated secondary antibody. Anysomicin treated cells were used as positive control for the detection of pp38. The level of β-actin is shown at the bottom as a loading control. One representative experiment of three independent experiments is shown.