Calcium mobilization in human myeloid cells results in acquisition of individual dendritic cell-like characteristics through discrete signaling pathways

We have shown previously that calcium ionophore (CI) treatment of various m yeloid origin cells results in rapid acquisition of properties associated w ith mature, activated dendritic cells. These properties include increased C D83 and costimulatory molecule expression, tendencies to form dendritic pro cesses, loss of CD14 expression by monocytes, and typically an enhanced cap acity to sensitize T lymphocytes to Ag, We here analyze the intracellular s ignaling pathways by which CI induces acquisition of such properties. Thaps igargin, which raises intracellular Ca2+ levels by antagonizing its sequest ration, induced immunophenotypic and morphologic changes that paralleled CI treatment. CI-induced activation was broadly attenuated by the Ca2+ chelat ing compound EGTA and by calmodulin antagonists trifluoperazine dimaleate a nd W-7, However, antagonists of signaling pathways downstream to calmodulin displayed more selective inhibitory effects: Calcineurin antagonists cyclo sporin A and the FK-506 analogue, ascomycin, diminished costimulatory molec ule and CD83 expression, as well as formation of dendritic processes in CI- treated myeloid cells, and strongly attenuated the T cell allosensitizing c apacity of CI-treated HL-60 cells. These calcineurin antagonists displayed minimal effect on CI-induced CD14 down-regulation in monocytes, In contrast , the calmodulin dependent protein kinase antagonists, K252a and KT5926, wh ile displaying only modest effects on CI-induced costimulatory molecule and CD83 expression, strongly blocked CD14 down-regulation. These results are consistent with a Ca2+-dependent mechanism for CI-induced differentiation o f myeloid cells, and indicate that multiple discrete signaling pathways dow nstream to calcium mobilization and calmodulin activation may be essential in regulating this process.