Epo-induced Ba/F3-d392 cells, like BA/F3-WT cells, increase Bcl-X_L mRNA levels, but do not induce MAPK tyrosine phosphorylation or p70^S6K activation. (A) Ba/F3-WT and -d392 cells stimulated with or without 50 U/mL of Epo for 30 minutes in the presence of SS or 50% FCS were lysed and subjected to immunoprecipitation with anti-MAPK antibodies and Western analysis with 4G10. The lower panel is a reprobing with anti-MAPK antibodies to show equal loading. (B) Ba/F3-WT and Ba/F3-d392 cells were starved for 4 hours in RPMI 1640 plus 0.1% BSA (lane 1), stimulated for 90 minutes with 5 U/mL Epo (lane 2) or 5 U/mL Epo + 10% FCS (lane 3), and total cellular RNA subjected to Northern blot analysis with bcl-x_L, bcl-2 and GAPDH probes as described in Materials and Methods. (C) Ba/F3-WT and Ba/F3-d392 cells were starved for 4 hours in RPMI 1640 plus 0.1% BSA, incubated with 5 U/mL Epo for 0, 30, 60, and 120 minutes and then lysed, immunoprecipitated with anti-p70^S6K antibodies, and the immunoprecipitate subjected to an in vitro kinase assay using the substrate peptide S610. The results are representative of two independent experiments.