Differential inside-out activation of beta2-integrins by leukotriene B4 and fMLP in human neutrophils.

We have investigated how LTB4, an endogenous chemoattractant encountered early in the inflammatory process, and fMLP, a bacteria-derived chemotactic peptide emanating from the site of infection, mediate inside-out regulation of the beta2-integrin. The role of the two chemoattractants on beta2-integrin avidity was investigated by measuring their effect on beta2-integrin clustering and surface mobility, whereas their effect on beta2-integrin affinity was measured by the expression of a high affinity epitope, a ligand-binding domain on beta2-integrins, and by integrin binding to s-ICAM. We find that the two chemoattractants modulate the beta2-integrin differently. LTB4 induces an increase in integrin clustering and surface mobility, but only a modest increase in integrin affinity. fMLP evokes a large increase in beta2-integrin affinity as well as in clustering and mobility. Lipoxin, which acts as a stop signal for the functions mediated by pro-inflammatory agents, was used as a tool for further examining the inside-out mechanisms. While LTB4-induced integrin clustering and mobility were inhibited by lipoxin, only a minor inhibition of fMLP-induced beta2-integrin avidity and no inhibition of integrin affinity were detected. The different modes of the inside-out regulation of beta2-integrins suggest that distinct mechanisms are involved in the beta2-integrin modulation induced by various chemoattractants.

Novel prostaglandin D(2)-derived activators of peroxisome proliferator-activated receptor-gamma are formed in macrophage cell cultures.

Incubation of RAW 264.7 murine macrophages with 9,15-dihydroxy-11-oxo-, (5Z,9alpha,13E,15(S))-Prosta-5,13-dien-1-oic acid [prostaglandin D(2) (PGD(2))] induced formation of considerable peroxisome proliferator-activated receptor-gamma (PPARgamma) activity [Nature 391 (1998) 79]. Because PGD(2) itself is a poor PPARgamma ligand, we incubated RAW 264.7 macrophage cultures with prostaglandin D(2) for 24 h and studied the ability of the metabolites formed to activate PPARgamma. PGD(2) products were extracted and fractionated by reverse phase high-performance liquid chromatography. Chemical identification was achieved by UV spectroscopy, gas-liquid chromatography/mass spectrometry and chemical syntheses of reference compounds. PGD(2) was converted to eight products, six of which were identified. Ligand-induced interaction of PPARgamma with steroid receptor coactivator-1 was determined by glutathione-S-transferase pull-down assays and PPARgamma activation was investigated by transient transfection of RAW 264.7 macrophages. In addition to the previously known ligand 11-oxo-(5Z,9,12E,14Z)-Prosta-5,9,12,14-tetraen-1-oic acid (15-deoxy-delta(12,14)-PGJ(2)), a novel PPARgamma ligand and activator viz. 9-hydroxy-11-oxo-, (5Z,9alpha,12E,14Z)-Prosta-5,12,14-trien-1-oic acid (15-deoxy-delta(12,14)-PGD(2)) was identified. The biological significance of these results is currently under investigation.