The carboxyl terminus of bradykinin and amino terminus of the light chain of kininogens comprise an endothelial cell binding domain.

Bradykinin (BK), a potent vasoactive nonapeptide formed by proteolytic cleavage of kininogen, mediates its activity by binding to specific cell surface receptors. Delivery of BK to these receptors is limited by cell-bound and plasma kininases that degrade BK to inactive fragments. Binding of its parent compound, kininogen, to specific endothelial cell receptors may provide an environment in which the degradation of BK by kininases is restricted. The determinants that mediate kininogen binding to endothelial cells have not been fully elucidated. The present studies suggest that part of BK and the amino-terminal amino acids of kininogens' common light chain constitute part of this recognition sequence. Human umbilical vein endothelial cells (HUVEC) in culture at 37 degrees C express 2-3-fold more binding sites for biotinylated high molecular weight kininogen (biotin-HK) containing BK than for biotin-HK from which BK has been liberated by plasma kallikrein. Binding of BK-free biotin-HK was not restored by preincubating HUVEC with BK, arguing against the possibility that BK released from biotin-HK stimulated expression of additional HK receptors. The extent of biotin-HK binding to HUVEC at 37 degrees C directly correlated with the amount of BK retained within the protein. Four lines of evidence suggest that part of BK and the amino terminus of the light chain of kininogens are part of the sequence recognized by the endothelial cell kininogen receptor. First, monoclonal antibodies to the carboxyl terminus of BK (MBK3) and the common light chains of the kininogens (HKL6, HKL8) inhibited biotin-HK binding to HUVEC. Second, a synthetic, dimeric bradykinin receptor antagonist blocked biotin-HK (IC50 = 9 microM) binding to HUVEC as did two synthetic tissue kallikrein inhibitors modeled after the carboxyl-terminal sequence of BK. Third, synthetic peptides containing the carboxyl-terminal portion of BK and the amino terminus of kininogens' common light chain, MKRPPGFSPFRSSRIG and GFSPFRSSRIG, blocked binding of biotin-HK (IC50 = 2-3 mM), whereas an overlapping peptide, SPFRSSRIGEIKEETT, at 5 mM and a scrambled peptide, FSGPKRSPIMGRPSFR, did not. Fourth, biotinylated GMKRPPGFSPFRSSRIG specifically bound to HUVEC, and its binding was blocked by HK. Since the presence of the nonapeptide BK in HK contributes to maximal binding of HK to HUVEC, there is a novel type of BK receptor in which part of the nonapeptide is recognized within the context of its parent molecule.(ABSTRACT TRUNCATED AT 400 WORDS)