MODULATION OF THE ALVEOLAR MACROPHAGE SUPEROXIDE PRODUCTION BY PROTEIN-PHOSPHORYLATION

Stimulation of alveolar macrophages (AM) with adenosine-5-diphosphate (ADP) results in transient production of superoxide anion radical (O-2 (.-); superoxide) and H2O2 in a metabolic event known as the respirato ry burst, initiation of the respiratory burst appears to depend on act ivation of protein kinase activity, whereas protein phosphatases might involved in termination of the burst. The involvement of protein kina se C was suggested by inhibition by bisindolylmaleimide I (GF 109203X) , a relatively specific inhibitor. KN-62, an inhibitor of calcium-calm odulin protein kinase II, also partly inhibited the respiratory burst stimulated by ADP and phorbol esters. The role of protein phosphatases in termination of the ADP-stimuiated respiratory burst of AM was exam ined with calyculin A (CA) (25-75 nM) or okadaic acid (OA) (1-5 mu M), two inhibitors of protein phosphatase 1 and 2a (PP1;PP2a). A dose-dep endent prolongation of the respiratory burst was observed in the prese nce of these inhibitors. CA and OA also markedly enhanced the rate of superoxide production stimulated by ADP, consistent with involvement o f PP1/PP2a in regulating both the rate of activation and timing of ter mination. Treatment of AM with cyclosporin A (CsA) (1-50 mu M), an inh ibitor of the calcium-dependent protein phosphatase 2b (PP2b), stimula ted superoxide production by itself and significantly prolonged the du ration of ADP-stimulated superoxide production. CsA, however, did not increase the ADP-stimulated rate of superoxide production. Thus, PP1/P P2a appear to be the primary phosphatases for controlling the intensit y oi the respiratory burst during receptor-elicited superoxide product ion in AM, whereas PP1/PP2a and PP2b play a role in turning off the re spiratory burst.