Differential inhibition in proliferation of G1E-ER2 cells by p38 inhibitor and stromal cells expressing different isoforms of SCF.

G1E-ER2 cells were cocultured for 48 hours with mitomycin C–treated stable stromal cell transfectants expressing S-SCF, MA-SCF, MR-SCF, or rrSCF in the absence or presence of indicated concentrations of the p38 inhibitor SB203580. (A) Proliferation was measured by thymidine incorporation assay. Bars denote the mean inhibition in proliferation (± SEM) of 2 independent experiments in the presence of an increasing concentration of SB203580 performed in replicates of 6. *P < .05 S-SCF and rrSCF (12.5 and 25 μM) versus MA-SCF (12.5 and 25 μM) and MR-SCF (12.5 and 25 μM). (B) Level of p38 inhibition in G1E-ER2 cells treated with 12.5 or 25 μM SB203580 and stimulated with soluble SCF or MR-SCF. Lanes 1 and 5: unstimulated G1E-ER2 cells. Lanes 2 and 6: G1E-ER2 cells stimulated with soluble SCF and MR-SCF, respectively. Lanes 3 and 7: 12.5 μM SB203580 pretreated G1E-ER2 cells stimulated with soluble and MR-SCF, respectively. Lanes 4 and 8: 25 μM SB203580 pretreated G1E-ER2 cells stimulated with soluble and MR-SCF, respectively. Arrows indicate the phosphorylated and total p38 protein.