Stimulation of neutrophils by prenylcysteine analogs: Ca²⁺ release and influx

Farnesylthiosalicylic acid (FTS), a synthetic analog of the terminal prenylcysteine present in signaling proteins induces generation of superoxide ions, phospholipase C-driven hydrolysis of inositol lipids and calcium elevation in human neutrophils and DMSO-differentiated HL60 cells. These effects were ascribed to an interaction of the analog with elements responsible for recognition of specific prenylated proteins. The present study demonstrated that in addition to the release of intracellular calcium stores, FTS enhanced entry of Ca²⁺ and Mn²⁺ from the medium. The biphasic dependence of the influx on the concentration of FTS, as well as its insensitivity to inhibition by PMA and La³⁺ suggest that the influx pathway activated by FTS is distinct from the previously described store-operated calcium channels of neutrophils. Consistent with the participation of a cellular membrane component in the interaction, FTS enhanced ⁴⁵Ca uptake in neutrophils and neutrophil cell membranes, but not in multilamellar vesicles. To establish specificity of the farnesyl moiety of FTS (C₁₅), effects of three other analogs, geranylthiosalicylate, GTS (C₁₀), geranylgeranylthiosalicylate, GGTS (C₂₀), as well as the carboxymethyl ester FTS-Me on calcium homeostasis and superoxide production were investigated. GGTS dose-dependently elevated [Ca²⁺](i), induced quenching of the 360 nm Fura-2-calcium fluorescence by Mn²⁺ and stimulated superoxide release, while GTS and FTS-Me were inactive. These results defined specific structural requirements for the functional interaction of prenylcysteine analogs with myeloid cells. Copyright (C) 1999 Elsevier Science B.V.