Roles of the mitogen-activated protein kinase family in macrophage responses to colony stimulating factor-1 addition and withdrawal

Colony stimulating factor-1 (CSF-1) (or macrophage CSF) is involved in the survival, proliferation, differentiation, and activation of cells of the mo nocyte/macrophage lineage. Because the mitogen-activated protein kinase fam ily members extracellular signal-regulated kinases (ERKs), p38, and c-Jun N -terminal kinase are widely implicated in such cellular functions, we measu red their activity in growing and growth-arrested cultures of bone marrow-d erived macrophages (BMM), as well as their stimulation by saturating concen trations of CSF-1, ERK activity was approximately a-fold higher in cycling BMM compared with growth-arrested BMM; in addition, CSF-l-stimulated BMM DN A synthesis was partially inhibited by PD98059, a specific inhibitor of MEK activation, suggesting a role for a mitogen-activated protein-ERK kinase ( MEK)/ERK pathway in the control of DNA synthesis but surprisingly not in th e control of cyclin D1 mRNA or c-myc mRNA expression. The suppression of BM M apoptosis by CSF-1, i.e, enhanced survival, was not reversed by PD98059, suggesting that a MEK/ERK pathway is not involved in this process. Using a quantitative kinase assay, it was found that CSF-1 gave a slight in crease in BMM p38 activity, supporting prior data that CSF-1 is a relativel y weak stimulator of inflammatory cytokine production in monocytes/macropha ges, Relatively high concentrations of the p38 inhibitor, SKB202190, suppre ssed CSF-l-stimulated BMM DNA synthesis. No evidence could be obtained for the involvement of p38 activity in BMM apoptosis following CSF-1 withdrawal . We were not able to show that CSF-1 enhanced BMM JNK-1 activity to a sign ificant extent; again, no role could be found for JNK-1 activity in the BMM apoptosis occurring after CSF-1 removal.