Antagonists of calcium fluxes and calmodulin block activation of the p21-activated protein kinases in neutrophils

Neutrophils stimulated with fMLP or a variety of other chemoattractants that bind to serpentine receptors coupled to heterotrimeric G proteins exhibit rapid activation of two p21-activated protein kinases (Paks) with molecular masses of ∼ 63 and 69 kDa (γ- and α-Pak). Previous studies have shown that products of phosphatidylinositol 3-kinase and tyrosine kinases are required for the activation of Paks. We now report that a variety of structurally distinct compounds which interrupt different stages in calcium/calmodulin (CaM) signaling block activation of the 63- and 69-kDa Paks in fMLP-stimulated neutrophils. These antagonists included selective inhibitors of phospholipase C (1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole -2,5-dione), the intracellular Ca²⁺ channel (8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate), CaM (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide; N-(4-aminobutyl)-5-chloro-1-naphthalenesulfonamide; trifluoperazine), and CaM-activated protein kinases (N-[2-(N-(chlorocinnamyl)-N-methylaminomethyl)phenyl]-N-[2-hydroxyethyl]-4-me thoxybenzenesulfonamide). This inhibition was dose-dependent with IC₅₀ values very similar to those that interrupt CaM-dependent reactions in vitro. In contrast, less active analogues of these compounds (1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-2,5-pyrrol idinedione; N-(6-aminohexyl)-1-naphthalenesulfonamide; N-(4-aminobutyl)-1-naphthalenesulfonamide; promethazine; 2-[N-(4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzyl-ami ne]) did not affect activation of Paks in these cells. CaM antagonists (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide; trifluoperazine), but not their less-active analogues (N-(6-aminohexyl)-1-naphthalenesulfonamide; promethazine), were also found to block activation of the small GTPases Ras and Rac in stimulated neutrophils along with the extracellular signal-regulated kinases. These data strongly suggest that the Ca²⁺/CaM complex plays a major role in the activation of a number of enzyme systems in neutrophils that are regulated by small GTPases.