IAP

Integrin Associated Protein (IAP, CD47) is a single chain glycoprotein that, on the basis of its primary structure, has 5 potential membrane-spanning regions and a large extra-cytoplasmic amino terminus with homology to the IgV domain of the immunoglobulin superfamily (Lindberg et al 1993; Lindberg et al 1994). It is expressed widely. It appears to be associated with Ñ3-integrins (Brown et al 1990), but its expression is not limited to cells expressing integrins (Rosales et al 1992). IAP may function as a calcium channel (Schwartz et al 1993), or as a signal transduction unit, modulating the effect of integrin function (Zhou et al 1993), possibly via interaction with the cytoplasmic tail of the Ñ3-integrin (Blystone et al 1995). Cooper et al show the critical dependence of transmigration on IAP function (Cooper et al 1995). Treatment of neutrophils with blocking antibodies inhibited chemotactic and cytokine activated transmigration by >80%, and inhibited neutrophil chemotaxis. This appears to be the case with monocyte transmigration (Weerasinghe et al 1998); in this case it seems IAP acts as a regulator of Ñ3 integrin, which in turn modulates LFA-1, and presumably inhibits transmigration by inhibiting leukocyte motility. This is in keeping with the slowing of inflammatory responses seen in IAP knockout mice (Lindberg et al 1996). In contrast, when the endothelium alone is treated with IAP-blocking antibodies, only cytokine-activated transmigration is inhibited (Cooper et al 1995). Although there is no data to specifically link it to passage through the junction, and the mechanism of action on the endothelium is unclear, the lack of inhibition of adhesion and its effects on [Ca++]i provide some suggestion that it may be critical in this phase of migration.

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