Signal transduction pathways in normal human monocytes stimulated by cytokines and mediators: Comparative study with normal human neutrophils or transformed cells and the putative roles in functionality and cell biology

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin ( IC) -3 induced tyrosine phosphorylation of 92-kDa protein in normal human m onocytes. We identified this 92-kDa protein as STAT5, but not as STATs1, 3, and 6 nor c-fes and vav protooncogene products, and demonstrated its trans location to the nucleus, enhancement of specific DNA binding capacity, and potentiation of trancriptional activity by GM-CSF. N-formyl-methionyl-leucy l-phenylalanine (FMLP) and phorbol myristate acetate (PMA) induced tyrosine phosphorylation of 42- and 44-kDa proteins, which were identified as extra cellular signal-regulated kinase (ERK), in human monocytes. In marked contr ast to neutrophils and MO7e cells, GM-CSF did not induce tyrosine phosphory lation and activation of ERK in monocytes. Among upstream signaling molecul es of ERK, She was constitutively associated with Grb2 and was not tyrosine -phosphorylated by GM-CSF and FMLP, and Sos1 and c-Raf-l were not phosphory lated by GM-CSF, IL-3, TNF, and FMLP in monocytes, whereas all these signal ing molecules were affected and/or utilized by GM-CSF in MO7e cells. In con trast to neutrophils, p38 was constitutively phosphorylated and agonist-dep endent phosphorylation and activation was not detected in human monocytes. Superoxide release stimulated by FMLP was inhibited partially by PD98059 or SB203580, a specific inhibitor of ERK or p38 pathway, and was almost compl etely inhibited by the combination of both inhibitors, whereas PMA-induced superoxide release was resistant to these two inhibitors in monocytes. PD98 059 inhibited GM-CSF-dependent proliferation of MO7e cells. Present results indicate trancriptional roles of STATS and functional roles of ERK and/or p38 in normal human monocytes stimulated by physiological receptor-mediated agonists GM-CSF and FMLP. Possible roles of ERK in proliferation of transf ormed cells were also suggested. (C) 1999 International Society for Experim ental Hematology. Published by Elsevier Science Inc.