2) in a manner that is dose dependent (Fig

2) in a manner that is dose dependent (Fig. diminished effect. Binding of sgC1qR to ECs was through surface-bound fibrinogen and was inhibited by anti-fibrinogen. In summary, our data suggest that, at sites of inflammation, sgC1qR can enhance vascular permeability by upregulation of B1R expression through de novo synthesis, as well as rapid translocation of preformed B1R. == Introduction == The endothelial cell (EC) receptor for high m.w. kininogen (HK)the bradykinin (BK) precursorconsists of receptor for the GW3965 globular heads of C1q (gC1qR), cytokeratin 1, and urokinase-type plasminogen activator receptor (uPAR), which are organized into two bimolecular complexes: uPARcytokeratin 1 and gC1qRcytokeratin 1 (17). Within this complex, gC1qR serves as a strictly zinc-dependent high-affinity site for HK and, therefore, is critical for the assembly and activation of the plasma KininKallikrein system (KKS), leading to the generation of BK (1,5). The KKS consists of three essential proteins that interact in vivo in a complex fashion once bound to a macromolecular complex formed during an inflammatory response or bound to proteins along cell surfaces (8). These are coagulation factor XII (FXII; or Hageman factor), prekallikrein (PK), and HK. Although FXII preferentially binds to the uPAR-cytokeratin 1 complex, HK, which circulates in complex with PK, binds to residues located in its domain 5 (8). Once FXII is activated to factor XIIa, it converts PK to kallikrein, a process that is enhanced by heat shock protein 90 and/or the enzyme carboxypeptidase released by ECs (9). In turn, kallikrein generated in this manner digests HK to generate the nonapeptide BK (NH2-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-OH) (8). BK belongs to the kinin family of proinflammatory peptides and is among the most potent vasodilator agonists known (10,11). Once generated, it GW3965 is rapidly converted to des-Arg9-BK by carboxypeptidase N, which removes the C-terminal arginine (11). BK induces its activity via two G proteincoupled receptors: BK receptor 2 (B2R) and BK receptor 1 (B1R). Although B2R is ubiquitously and constitutively expressed on many healthy cell types, including ECs, B1R is expressed at low levels, but is induced rapidly, after tissue damage by IL-1 (12). Furthermore, although BK has a higher affinity for B2R, des-Arg9-BK GW3965 is a selective ligand for B1R. Activation of both receptors, in turn, is known to contribute to a plethora GW3965 of acute and chronic SQSTM1 pathological disorders, including hypotension, bronchoconstriction, pain, and inflammation (13,14). During the inflammatory response, activated cells, including ECs, are known to overexpress and to secrete and/or release soluble gC1qR (sgC1qR). sgC1qR, in turn, binds to intact cells in an autocrine/paracrine manner (15). Therefore, the present studies were undertaken to identify the cell surface entity that is the site for sgC1qR and to assess the possibility that bound sgC1qR GW3965 is able to induce B1R expression. The results of these findings are discussed, and the biological relevance is underscored. == Materials and Methods == == Chemicals and reagents == The following reagents and chemicals were used. Dulbeccos PBS (D-PBS) with and without calcium and magnesium was obtained from Mediatech (Manassas, VA). DMEM, RPMI 1640, and 100 Penicillin/Streptomycin were obtained from Life Technologies-Invitrogen (Grand Island, NY). Heat-inactivated FBS was from HyClone (Logan, UT). Human serum albumin was obtained from Immuno U S (Rochester, MI), and Immu-Mount was from Thermo Fisher (Waltham, MA). Alexa Fluor 488streptavidin or Alexa Fluor 594streptavidin, Alexa Fluor 488F(ab)2or Alexa Fluor 594F(ab)2,goat anti-mouse or anti-rabbit, FITC-conjugated goat anti-mouse IgG F(ab)2, and sheep anti-rabbit IgG F(ab)2were from Invitrogen (Carlsbad, CA).p-nitrophenyl phosphate and alkaline phosphataseconjugated rabbit anti-goat IgG were from Pierce (Rockford, IL). == Expression of recombinant gC1qR and its deletion mutants == The strategy for the construction of plasmids containing full-length gC1qR, as well as deletion mutants lacking highly charged domains identified from the crystal structure (16), were described in detail in our earlier publications (1719). == Cultured cells == Human brain microvascular ECs were cultured in Endothelial Cell Growth Medium-2 (Lonza, Walkersville, MD) containing 5% heat-inactivated FBS, as described (20). Cells grown to confluence on 2% gelatin were treated first (30 min, 37C) with 0.25% trypsin, 0.01% EDTA in 0.01 M TBS, to dissociate cells from the gelatin matrix by incubation. The cells were then washed and cultured in DMEM. Experiments were done with cells between passages 3 and 15. The U937 cell line was grown in suspension in RPMI 1640 containing 10% heat-inactivated FBS, 100 U/ml penicillin, and 100 g/ml.

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