STIMULUS-RESPONSE COUPLING IN FMLP-STIMULATED U937 MONOCYTES - EFFECT OF DIFFERENTIATION ON GI2 EXPRESSION

The effect of differentiation on FMLP-stimulated InsP production and G-protein expression was investigated in U937 monocytes. FMLP (0.01-10 μM) stimulated [3H]InsP production in dimethyl sulphoxide-differentiated, but not in immature, U937 cells. Ionomycin (1 and 10 μM) stimulated [3H]InsP production equally well in both cell types. The FMLP response was blocked by pertussis toxin (100 ng/ml for 4 h) which catalysed [32P]ADP ribosylation of a 40 kDa 'Gi-like' G-protein α subunit in these cells. This protein was also identified immunologically using anti-peptide antibodies that detect 'Gi-like' α subunits (SG2) or Gi2α specifically (LE2). With LE2 a 5-fold increase in Gi2α levels was seen following differentiation of the cells, suggesting that FMLP receptor expression is accompanied by an increase in the G-protein with which these receptors interact. © 1990.