IFN-γ enhances expression of formyl peptide receptors and guanine nucleotide-binding proteins by HL-60 granulocytes

Abstract

Exposure to IFN-γ increases the respiratory burst of polymorphonuclear leukocytes stimulated by the chemoattractant FMLP. However, the mechanism by which IFN-γ alters the response to FMLP is unclear. We addressed the hypothesis that IFN-γ enhances the response to FMLP by regulating the expression of elements of the formyl peptide receptor transmembrane-signaling pathway. HL-60 granulocytes were used as a model of FMLP transmembrane signaling. Formyl peptide receptor number and affinity were studied in isolated plasma membranes prepared from control HL-60 cells (CM) and cells exposed to IFN-γ 100 U/ml for 24 h (IFN-M). Formyl peptide receptors were significantly increased on IFN-M compared with CM (1473 +/- 300 vs 3209 +/- 924). FMLP stimulates increased guanine nucleotide-binding protein (G protein) activation in IFN-M as evidenced by enhanced guanosine 5’-[γ-thio]triphosphate binding and GTPase activity. Gi sub-unit content was increased in IFN-M as measured by pertussis toxin-catalyzed ADP-ribosylation and immunoblotting with antibodies against α i2 and α i3 G protein subunits. Guanosine 5’-[γ-thio]triphosphate equilibrium binding demonstrated an increased number of G proteins coupled to formyl peptide receptors on IFN-M. We conclude that IFN-γ increases expression of both formyl peptide receptors and G proteins coupled to these receptors, thereby enhancing FMLP-stimulated transmembrane signaling. Regulation of transmembrane signaling element expression may be a significant mechanism by which IFN-γ regulates cellular functions.