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Vol. 18, Issue 2, 441-454, February 2007
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*Laboratory of Molecular Pharmacology, Biosignal Research Center, Kobe University, Kobe 657-8501, Japan;
Molecular Defenses Section, Laboratory of Host Defenses, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and
Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan
Submitted August 21, 2006;
Revised November 13, 2006;
Accepted November 14, 2006
Monitoring Editor: Ralph Isberg
In the phagocytic cell, NADPH oxidase (Nox2) system, cytoplasmic regulators (p47phox, p67phox, p40phox, and Rac) translocate and associate with the membrane-spanning flavocytochrome b558, leading to activation of superoxide production. We examined membrane targeting of phox proteins and explored conformational changes in p40phox that regulate its translocation to membranes upon stimulation. GFP-p40phox translocates to early endosomes, whereas GFP-p47phox translocates to the plasma membrane in response to arachidonic acid. In contrast, GFP-p67phox does not translocate to membranes when expressed alone, but it is dependent on p40phox and p47phox for its translocation to early endosomes or the plasma membrane, respectively. Translocation of GFP-p40phox or GFP-p47phox to their respective membrane-targeting sites is abolished by mutations in their phox (PX) domains that disrupt their interactions with their cognate phospholipid ligands. Furthermore, GFP-p67phox translocation to either membrane is abolished by mutations that disrupt its interaction with p40phox or p47phox. Finally, we detected a head-to-tail (PXPhox and Bem1 [PB1] domain) intramolecular interaction within p40phox in its resting state by deletion mutagenesis, cell localization, and binding experiments, suggesting that its PX domain is inaccessible to interact with phosphatidylinositol 3-phosphate without cell stimulation. Thus, both p40phox and p47phox function as diverse p67phox "carrier proteins" regulated by the unmasking of membrane-targeting domains in distinct mechanisms.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
Address correspondence to: Naoaki Saito (naosaito{at}kobe-u.ac.jp)
Abbreviations used: AA, arachidonic acid; Fc
R, Fc
receptor; PA, phosphatidic acid; ROS, reactive oxygen species.
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