Transcriptional and ERK1/2-dependent synergistic upregulation of p21(cip1/waf1) associated with steel factor synergy in MO7e

Steel factor (SLF) plus GM-CSF induces proliferative synergy in myeloid pro genitors and factor-dependent cell line MO7e. We previously reported that t he protein level of cyclin-dependent kinase inhibitor p21(cip1/waf1) (p21) increased synergistically when MO7e cells were stimulated with SLF plus GM- CSF and that p21 induction was required for SLF synergistic responses. Here we show that this p21 induction is regulated at the transcriptional level. Based on use of a multiprobe RNase protection assay, the synergistic incre ase of p21 mRNA was unique among many cell cycle regulators. While STAT5A a nd 5B were activated after stimulation with GM-CSF alone or SLF plus GM-CSF , there was no difference in activation between the groups. p44/42 MAP kina se (ERK1/2) was synergistically activated by SLF plus GM-CSF, but SAPK/JNK and p38 MAP kinase were not. Synergistic induction of p21 was significantly decreased with a MEK1 inhibitor, suggesting that the ERK1/2 pathway is inv olved in the synergistic increase of p21 after GM CSF plus SLF stimulation. (C) 2001 Academic Press.