Modulation of transmembrane signalling in HL-60 granulocytes by tumour necrosis factor-alpha

Differentiated HL-60 granulocytes were used to study the mechanism by which tumour necrosis factor-alpha (TNF) enhances responses to N-formyl-methionyl-leucylphenylalanine (FMLP). Cultivation of differentiated HL-60 cells with 100 units of TNF/ml for 24 h resulted in a 3-fold increase in superoxide release and 4-fold increase in prostaglandin E2 production on stimulation with 1 microM-FMLP. On the other hand, cultivation with TNF failed to increase phorbol diester stimulation of superoxide release. Formyl-peptide-receptor expression determined on isolated membranes from cells cultivated with TNF (TNF-M) was increased by 50% compared with membranes from control cells (NM). Similarly, FMLP binding to intact HL-60 cells was increased by cultivation with TNF. Guanine-nucleotide-binding proteins (G-protein) levels were not different between TNF-M and NM, as determined by pertussis-toxin-catalysed ADP-ribosylation and by immunoblotting with antisera recognizing alpha i2 subunit. Binding of guanosine 5'-[gamma-thio]triphosphate and GTP hydrolysis stimulated by FMLP were enhanced by about 50% in TNF-M. The efficiency of G-protein activation by formyl-peptide receptors did not differ between TNF-M and NM. TNF regulates expression of formyl-peptide receptors independently of G-protein levels. The regulation of receptor expression is one mechanism by which TNF enhances cell responses to formylated peptides.