Evaluation of signal transduction pathways in chemoattractant-induced human monocyte chemotaxis

The intracellular signaling pathways involved in human monocyte chemotaxis toward a variety of chemoattractant molecules were evaluated using selected pharmacological agents. Neither phosphatidylinositol-3-kinase (PI3 K) or e xtracellular signal-regulated kinase (ERK) activity were required for monoc yte migration toward monocyte chemoattractant protein-1 alpha (MCP-1 alpha) , RANTES (Regulated on Activation, Normal T cell Expressed and Secreted), m acrophage inflammatory protein-la (MIP-la) or formyl-Met-Leu-Phe (fMLP), si nce pretreatment with wortmannin or LY294002, or with PD098059, had no effe ct on the chemotactic response. Addition of forskolin and IBMX significantl y attenuated chemotaxis to each of these chemoattractants and was reversed by co-treatment with Rp-cAMP, a competitive inhibitor of cAMP-dependent pro tein kinase A. Incubation with the protein kinase C (PKC) inhibitor GF10920 3X-HCl (GF109) did not affect monocyte migration, but pretreatment of monoc ytes with PMA significantly impaired the response to each of these chemotac tic agents. Inhibition by PMA was reversed by co-treatment with GF109, impl ying that heterologous PKC activation is capable of desensitizing chemokine and fMLP-induced monocyte chemotaxis. These results help to define the sig nalling pathways involved in human monocyte chemotaxis and suggest pharmaco logical approaches to evaluating the cross-desensitization of chemoattracta nt-induced leukocyte migration.