Role of phosphatidylinositol 3-kinase in the binding ofBordetella pertussisto human monocytes

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Abstract
Bordetella pertussis, the causative agent of whooping cough, adheres to human monocytes by means of filamentous haemagglutinin (FHA), a bacterial surface protein that is recognized by complement receptor type 3 (CR3, αMβ2 integrin). Previous work has shown that an FHA Arg‐Gly‐Asp (RGD, residues 1097–1099) site interacts with a complex composed of leucocyte response integrin (LRI, αvβ3 integrin) and integrin‐associated protein (IAP, CD47) on human monocytes, resulting in enhancement of CR3‐mediated bacterial binding. However, the pathway that mediates αvβ3‐αMβ2 integrin signalling remains to be characterized. Here we describe the involvement of phosphatidylinositol 3‐kinase (PI3‐K) in this pathway. Wortmannin and LY294002, inhibitors of PI3‐K, reduced αvβ3/IAP‐upregulated, CR3‐associated bacterial binding to human monocytes. B. pertussis infection of human monocytes resulted in a marked recruitment of cellular PI3‐K to the sites of B. pertussis contact. In contrast, cells infected with an isogenic strain carrying a G1098A mutation at the FHA RGD site did not show any recruitment of PI3‐K. We found that ligation of FHA by αvβ3/IAP induced RGD‐dependent tyrosine phosphorylation of a 60 kDa protein, which associated with IAP and PI3‐K in human monocytes. These results suggest that PI3‐K and a tyrosine phosphorylated 60 kDa protein may be involved in this biologically important integrin signalling pathway.