Roles for beta II-protein kinase C and RACK1 in positive and negative signaling for superoxide anion generation in differentiated HL60 cells

beta-Protein kinase (PKC) is essential for ligand-initiated assembly of the NADPH oxidase for generation of superoxide anion (O(2)). Neutrophils and neutrophilic HL60 cells contain both betaI and betaII-PKC, isotypes that are derived by alternate splicing. betaI-PKC-positive and betaI-PKC null HL60 cells generated equivalent amounts of O(2) in response to fMet-Leu-Phe and phorbol myristate acetate. However, antisense depletion of betaII-PKC from betaI-PKC null cells inhibited ligand-initiated O(2) generation. fMet-Leu-Phe triggered association of a cytosolic NADPH oxidase component, p47(phox), with betaII-PKC but not with RACK1, a binding protein for betaII-PKC. Thus, RACK1 was not a component of the signaling complex for NADPH oxidase assembly. Inhibition of beta-PKC/RACK1 association by an inhibitory peptide or by antisense depletion of RACK1 enhanced O(2) generation. Therefore, betaII-PKC but not betaI-PKC is essential for activation of O(2) generation and plays a positive role in signaling for NADPH oxidase activation in association with p47(phox). In contrast, RACK1 is involved in negative signaling for O(2) generation. RACK1 binds to betaII-PKC but not with the p47(phox).betaII-PKC complex. RACK1 may divert betaII-PKC to other signaling pathways requiring beta-PKC for signal transduction. Alternatively, RACK1 may sequester betaII-PKC to down-regulate O(2) generation.