p40 super(phox) down-regulates NADPH oxidase activity through interactions with its SH3 domain

• Published in: The Journal of biological chemistry 1997-04, Vol.272 (14), p.9141-9146
• Main Authors: Sathyamoorthy, M, De Mendez, I, Adams, A G, Leto, T L
• Format: Article
• Language: English
• ISSN: 0021-9258

The NADPH oxidase of phagocytes generates microbicidal oxidants in response to a variety of stimuli. Its activation and assembly involve multiple SH3 domain interactions among several oxidase components. Here we present evidence that the cytosolic oxidase-associated protein, p40 super(phox), mediates down-regulation of NADPH oxidase through interactions with its SH3 domain. Recombinant p40 super(phox) was produced in several eukaryotic expression systems (insect, mammalian, and yeast) to explore its role in oxidase function in relation to domains involved in interactions with other factors, p47 super(phox) and p67 super(phox). p40 super(phox) inhibited oxidase activity in vitro when added to neutrophil membranes and recombinant p47 super(phox), p67 super(phox), and p21rac. Co-transfection of p40 super(phox) into K562 cells resulted in significant decreases ( similar to 40%) in whole cell oxidase activity. Furthermore, the isolated SH3 domain of p40 super(phox) was even more effective in inhibiting whole cell oxidase activity, consistent with experiments showing that this domain binds to the same proline-rich target in p47 super(phox) (residues 358-390) that interacts with p67 super(phox). In contrast, deletion of the carboxyl-terminal domain of p40 super(phox) that binds to p67 super(phox) did not relieve its oxidase inhibitory effects. Thus, p40 super(phox) appears to down-regulate oxidase function by competing with an SH3 domain interaction between other essential oxidase components.