Activation of p90(RSK) and cAMP response element binding protein in stimulated neutrophils: Novel effects of the pyridinyl imidazole SB 203580 on activation of the extracellular signal-regulated kinase cascade

Neutrophils stimulated with the chemoattractant FMLP or the phorbol ester P MA are known to exhibit activation of a 90-kDa renaturable protein kinase. Activation of this kinase was maximal at similar to 1-3 min after cell stim ulation and the time course for activation was similar to that of the extra cellular-regulated kinases (ERKs) and p38-mitogen activated protein kinase (p38(MAPK)). Compounds that block activation of ERK-1/2 (PD 98059) or that inhibit the activity of p38(MARK) (SB 203580) blocked activation of this 90 -kDa kinase. SE 203580 is a highly selective inhibitor of p38(MARK) in vitr o and is under intense study as a lead compound for developing novel anti-i nflammatory agents. However, we demonstrate that SB 203580 at concentration s greater than or equal to 10 mu M can also inhibit activation of ERK-1/2 i n neutrophils. An Ab to the protein kinase p90(RSK2) (also referred to as M APKAP-K1b, or p90(rsk)) immunoprecipitated the active 90-kDa kinase from ly sates of stimulated neutrophils. No activity was observed for this enzyme i n immunoprecipitates obtained from unstimulated cells, and the amounts of a ctivity were markedly reduced if the cells mere treated with PD 98059 or SE 203580 before stimulation. Neutrophils stimulated with FMLP exhibited phos phorylation of the cAMP response element binding protein (CREB), and this r eaction was inhibited by SB 203580 and PD 98059. These data establish that the renaturable 90-kDa protein kinase is p90(RSK2) and that CREB may be a s ubstrate for this enzyme in these cells. Novel effects of compound SB 20358 0 on stimulated neutrophils are also described.