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In the resting cell, the Pro-rich motif of p47phox interacts with the SH3 domain of p40phox, which in turn associates with p67phox. Upon activation, the p47-p40phox regulatory complex dissociates, permitting the association of p47phox with the COOH-terminal SH3 domain of p67phox. This complex translocates to the plasma membrane and associates with cytochrome b558, via interaction of the tandem SH3 domains of p47phox with the p22phox Pro-rich motif.

The regulation of the expression of the interleukin-8 (IL-81 gene m human monocytic cell lines has been investigated. Agents such as interleukin-1 (IL-l) or interferon-y (IFNy) did not induce increased IL-8 expression m THP-I or U937 cells. Bacterial lipopolysaccharide endotoxin (LPS) or phorbol myristate acetate (PMA) alone induced suboptimal expression as assessed by Northern blotting; however, preincubation of cells with PMA followed by endotoxin induced much higher levels of IL-8 mRNA. Incubation of the cells with the calcium ionophore A23187 resulted in consistent increased IL-S gene expression comparable to that of cells treated with endotoxm alone. In addition to inducing IL-8 mRNA this calcium ionophore also induced IL-8 protein synthesis as assessed by immunofluorescence and secretion as detected by ELISA. These results indicate that increases m intracellular calcium result in IL-8 gene expression and protein secretion.

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