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Blood, 1 January 2005, Vol. 105, No. 1, pp. 170-177.
Prepublished online as a Blood First Edition Paper on August 24, 2004; DOI 10.1182/blood-2004-02-0498.
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Submitted February 9, 2004
Accepted August 13, 2004
LDL-Receptor related protein regulates 2-integrin mediated leukocyte adhesion
Patricia P Spijkers, Paula da Costa Martins, Erik Westein, Carl G Gahmberg, Jaap J Zwaginga, and Peter J Lenting*
Laboratory for Thrombosis and Haemostasis, Department of Haematology, University Medical Center Utrecht, Utrecht, The Netherlands
Department of Experimental Immunohaematology, Sanquin Research, Amsterdam, The Netherlands
Department of Biological and Environmental Sciences, Division of Biochemistry, University of Helsinki, Helsinki, Finland
* Corresponding author; email: p.j.lenting{at}lab.azu.nl.
2-integrin clustering upon activation is a key event in leukocyte adhesion to the endothelium during the inflammatory response. Searching for molecular mechanisms leading to this clustering, we have identified LDL-receptor related protein (LRP) as a new partner for 2-integrins at the leukocyte surface. Immobilized recombinant LRP fragments served as an adhesive surface for blood-derived leukocytes and the U937 cell line. This adhesion was decreased up to 95 % in the presence of antibodies against 2-integrins, pointing to these integrins as potential partners for LRP. Using purified proteins, LRP indeed associated with the M 2 complex and the M and L I-domains (KD,app= 0.5 µM). Immunoprecipitation experiments and confocal microscopy revealed that endogenously expressed LRP and L 2 colocalized in monocytes and U937 cells. Furthermore, activation of U937 cells resulted in clustering of L 2 and LRP to similar regions at the cellular surface, indicating potential cooperation between both proteins. This was confirmed by the lack of L 2 clustering in U937 cells treated by antisense oligonucleotides to downregulate LRP. In addition, the absence of LRP resulted in complete abrogation of 2-integrin-dependent adhesion to endothelial cells in a perfusion system, demonstrating the presence of a previously unrecognised link between LRP and leukocyte function.

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