Cytosolic protein phosphatase may turn off activated NADPH oxidase in guinea pig neutrophils.

Protein phosphatase inhibitors, okadaic acid and calyculin A, potentiated and elongated N-formyl-methionyl-leucyl-phenylalanine-induced superoxide anion (O2-) production in guinea pig neutrophils. The activity of NADPH oxidase in the membrane fraction prepared from phorbol 12-myristate 13-acetate-stimulated neutrophils was inactivated by the addition of the cytosol from resting neutrophils, such inactivation of NADPH oxidase was also suppressed by the protein phosphatase inhibitors. We previously reported that phosphorylation of the 46-kDa protein by protein kinase C is one of the activation mechanisms of NADPH oxidase-dependent superoxide anion production. In the cytosol fraction, we found protein phosphatase activity that catalyzed dephosphorylation of 32P-labeled phosphoproteins including the 46-kDa protein. Dephosphorylation of the 46-kDa protein was inhibited by the addition of okadaic acid and calyculin A. These results indicate that dephosphorylation of the 46-kDa protein by protein phosphatase is involved in the inactivation of NADPH oxidase. NADPH oxidase activity in guinea pig neutrophil may be regulated by the phosphorylation/dephosphorylation state of the 46-kDa protein by protein kinase C and protein phosphatase.