Activation of p38 and JNK/SAPK, but not ERK, is required for stress-induced erythroid differentiation. SKT6 cells mixed with various concentrations (0 to 30 μmol/L) of antisense S-oligos (•) or sense S-oligos (○) of p38, JNK1, JNK2, ERKs (common to both ERK1 and ERK2), or scrambled S-oligos were (A) osmotic shocked or (B) heat shocked for 1 hour, and the percentage of hemoglobinized cells was counted after 4.5 days. The percentage of hemoglobinized cells after stress treatment without S-oligos is defined as 100%. Each point represents the mean of five replicates.