AJP - Lung Cellular and Molecular Physiology, Vol 273, Issue 5 1042-L1047, Copyright © 1997 by American Physiological Society
Ca(2+)-dependent p47phox translocation in hydroperoxide modulation of the alveolar macrophage respiratory burst
H. Zhou, R. F. Duncan, T. W. Robison, L. Gao and H. J. Forman
Department of Molecular Pharmacology and Toxicology, University of Southern California, Los Angeles 90033, USA.
Oxidative stress produces dual effects on the respiratory burst of rat
alveolar macrophages. Preincubation with hydroperoxide concentrations [H2O2
or tert-butyl hydroperoxide (t-BOOH); < 50 microM] enhances stimulation
of the respiratory burst, whereas higher concentrations inhibit
stimulation. Both the enhancement and inhibition are markedly attenuated by
buffering t-BOOH-induced changes in intracellular Ca2+ concentration
([Ca2+]i). Phosphorylation of the NADPH oxidase component p47phox and its
translocation from cytoplasm to plasma membrane are essential in
respiratory burst activation. Phorbol 12-myristate 13-acetate
(PMA)-stimulated p47phox phosphorylation was negligibly affected by 25 or
100 microM t-BOOH. Nonetheless, 25 microM t-BOOH increased PMA-stimulated
p47phox translocation, whereas 100 microM t-BOOH decreased PMA-stimulated
translocation. In unstimulated cells, however, neither phosphorylation nor
translocation of p47phox was affected by t-BOOH. Buffering of the
t-BOOH-mediated changes of [Ca2+]i abolished the effects of t-BOOH on
PMA-stimulated translocation in parallel to effects upon the respiratory
burst. The results suggest that the dual effects of hydroperoxides are
mediated, in part, by Ca(2+)-dependent processes affecting the assembly of
the respiratory burst oxidase at steps that are separate from p47phox
phosphorylation.
