Signal transduction pathways that contribute to myeloid differentiation.

The production of mature, differentiated myeloid cells is regulated by the action of hematopoietic cytokines on progenitor cells in the bone marrow. Cytokines drive the process of myeloid differentiation by binding to specific cell-surface receptors in a stage- and lineage-specific manner. Following the binding of a cytokine to its cognate receptor, intracellular signal-transduction pathways become activated that facilitate the myeloid differentiation process. These intracellular signaling pathways may promote myelopoiesis by stimulating expansion of a progenitor pool, supporting cellular survival during the differentiation process, or by directly driving the phenotypic changes associated with differentiation. Ultimately, pathways that drive the differentiation process converge on myeloid transcription factors, including PU.1 and the C/EBP family, that are critical for differentiation to proceed. While much is known about the cytokines, cytokine receptors and transcription factors that regulate myeloid differentiation, less is known about the precise roles that specific signaling mediators play in promoting myeloid differentiation. Recently, however, the application of novel pharmacologic inhibitors, siRNA strategies, and transgenic and knockout models has begun to shed light on the involvement and function of signaling pathways in normal myeloid differentiation. This review will discuss the roles that key signaling pathways and mediators play in myeloid differentiation.