Interaction of S100A8/S100A9 - Arachidonic acid complexes with the scavenger receptor CD36 may facilitate fatty acid uptake by endothelial cells

Recently, we showed that S100A8/A9 were secreted from phorbol ester-stimula ted neutrophil-like HL-60 cells, thereby carrying arachidonic acid [Kerkhof f et al. (1999) J. Biol. Chem. 274, 32672-32679], The present study was und ertaken to evaluate whether the secreted S100A8/A9-AA complex might be invo lved in transcellular eicosanoid metabolism. In the presence of S100A8/A9, arachidonic acid was rapidly taken up by human umbilical vein endothelial c ells in a saturable and energy-dependent fashion. Protein-facilitated arach idonate uptake was confirmed by its sensitivity toward the protein modifier s bromobimane and phloretin. Both potassium and sodium depletion did not af fect the arachidonate transport, indicating that arachidonate influx was in dependent of endocytosis. The uptake of exogenous arachidonic acid by HUVEC was predominantly mediated by FAT/CD36. This conclusion was drawn by the f indings that (i) arachidonate uptake was drastically inhibited by sulfo-N-s uccinimidyl oleate, a specific inhibitor of FAT/CD36; (ii) the maximal inhi bition of arachidonate uptake induced by SSO was similar to that effected b y ATP depletion; and (iii) the arachidonate transport was 2-fold higher in COS-7 cells transfected with the pEF.BOS-CD36 expression vector than in the empty vector-transfected COS-7 cells. Kinetic studies of arachidonate upta ke were indicative for an interaction between fatty acid transporter and S1 00A8/A9-AA complex that was confirmed by an in vitro protein-protein intera ction assay. FAT/CD36 has: been suggested to be involved in inflammatory re sponses, and S100A8/A9 are released from activated leukocytes at inflammato ry loci. Therefore, it can be envisioned that their interaction might propa gate host response by perpetuating recruitment and activation of cellular e ffectors.