Evidence for distinct intracellular signaling pathways in CD34(+) progenitor to dendritic cell differentiation from a human cell line model

Intracellular signals that mediate differentiation of pluripotent hemopoiet ic progenitors to dendritic cells (DC) are largely undefined. We have previ ously shown that protein kinase C (PKC) activation (with phorbol ester (PMA ) alone) specifically induces differentiation of primary human CD34(+) hemo poietic progenitor cells (HPC) to mature DC. We now find that cytokine-driv en (granulocyte-macrophage CSF and TNF-alpha) CD34(+) HPC --> DC differenti ation is preferentially blocked by inhibitors of PKC activation. To further identify intracellular signals and downstream events important in CD34(+) HPC --> DC differentiation we have characterized a human leukemic cell line model of this process. The CD34(+) myelomonocytic cell line KG1 differenti ates into dendritic-like cells in response to granulocyte-macrophage CSF pl us TNF-alpha, or PMA (with or without the calcium ionophore ionomycin, or T NF-alpha), with different stimuli mediating different aspects of the proces s. Phenotypic DC characteristics of KG1 dendritic-like cells include morpho logy (loosely adherent cells with long neurite processes), MHC I+/MHC IIbri ght/CD83(+)/CD86(+)/CD14(-) surface Ag expression, and RelB and DC-CK1 gene expression. Functional DC characteristics include fluid phase macromolecul e uptake (FITC-dextran) and activation of resting T cells. Comparison of KG 1 to the PMA-unresponsive subline KG1a reveals differences in expression of TNF receptors 1 and 2; PKC isoforms alpha, beta I, beta II, and mu; and Re lB, suggesting that these components/pathways are important for DC differen tiation. Together, these findings demonstrate that cytokine or phorbol este r stimulation of KG1 is a model of human CD34(+) HPC to DC differentiation and suggest that specific intracellular signaling pathways mediate specific events in DC lineage commitment.