Differential contribution of bradykinin receptors in angiogenesis

Endothelial-cell apoptosis induced by cleaved high-molecular-weight kininogen (HKa) is matrix dependent and requires the generation of reactive oxygen species

High-molecular-weight kininogen (HK) is an abundant plasma protein that plays a central role in activation of the kallikrein-kinin system. Cleavage of HK by plasma kallikrein results in release of the nonapeptide bradykinin (BK), leaving behind cleaved high-molecular-weight kininogen (HKa). Previous studies have demonstrated that HKa induces apoptosis of proliferating endothelial cells and inhibits angiogenesis in vivo, activities mediated primarily through its domain 5. However, the mechanisms by which these effects occur are not well understood. Here, we demonstrate that HKa induces apoptosis of endothelial cells cultured on gelatin, vitronectin, fibronectin, or laminin but not collagen type I or IV. The ability of HKa to induce endothelial-cell apoptosis is dependent on the generation of intracellular reactive oxygen species and associated with depletion of glutathione and peroxidation of endothelial-cell lipids, effects that occur only in cells cultured on matrix proteins permissive for HKa-induced apoptosis. Finally, the ability of HKa to induce endothelial-cell apoptosis is blocked by the addition of reduced glutathione or N-acetylcysteine. These studies demonstrate a unique role for oxidant stress in mediating the activity of an antiangiogenic polypeptide and highlight the importance of the extracellular matrix in regulating endothelial-cell survival.

Upregulation of Cdc2 and cyclin A during apoptosis of endothelial cells induced by cleaved high-molecular-weight kininogen

We (8) reported that the cleaved high-molecular-weight kininogen (HKa) and its domain 5 (D5) inhibited angiogenesis. Further studies (15) revealed that D5 could inhibit cell proliferation and induce apoptosis of proliferating endothelial cells, which together may represent a critical part of antiangiogenic activity of HKa and D5. In the present study, we further examined the effect of HKa on cell cycle progression and cell viability. We report that HKa induced a significant upregulation of Cdc2 and cyclin A in proliferating endothelial cells, concurrent with a marked increase of Cdc2 activity. The increased expression of Cdc2 and cyclin A by HKa was not associated with an apparent change in cell cycle profiles of basic fibroblast growth factor-stimulated proliferating cells, but closely correlated with a marked increase of apoptosis, suggesting that the elevated Cdc2 activity is involved in HKa-induced apoptosis of proliferating endothelial cells. Our results support an emerging hypothesis that Cdc2 and cyclin A are important regulators for cell cycle as well as for apoptosis.

Kininostatin as an antiangiogenic inhibitor: what we know and what we do not know

High-molecular-weight kininogen (HK) is a plasma protein consisting of six domains (designated D1-D6). It was first characterized as a precursor of bradykinin, a bioactive peptide that regulates many cardiovascular processes. HK can bind to endothelial cells where it can be cleaved by plasma kallikrein to release bradykinin contained within domain 4. The remaining portion of the molecule, cleaved HK, is designated HKa. While bradykinin has been intensively studied, the physiological implication of the generation of HKa is not clear. HKa has recently been shown to inhibit the important steps required for angiogenesis such as proliferation and migration of endothelial cells. The antiangiogenic activity of HKa has further been demonstrated in animal models in which HKa inhibits neovascularization. Because domain 5 (D5) of HKa reproduces the antiangiogenic effect of HKa, D5 is named kininostatin for this novel function. In this review, we will briefly discuss the recent progress in the studies of the molecular mechanisms that mediate the antiangiogenic effect of HKa and D5.

Molecular structure and alternative splicing of the human carboxypeptidase M gene

Using RACE technology the 5' and 3' ends of human carboxypeptidase M (CPM) mRNA were determined and found to be divergent from the published sequence. With these results the complete structure of the human CPM gene was established based on the human genome sequence in the GenBank database. The gene was shown to contain 9 exons comprising at least 75 kb of genomic sequence. A novel first exon of 30 bp was identified and an upstream promoter sequence containing several transcription factor binding sites was found by computer analysis. Furthermore, the ATG starting codon was detected defining an open reading frame of 1329 bp that codes for a protein of 443 residues. Additionally, the polyadenylation site was discovered, determining a 3' noncoding region of 2000 nucleotides. The exon-intron boundaries diverged substantially compared to those of the other basic carboxypeptidases, CPD, CPE, CPN, and AEBP1. Cloning and sequencing of RT-PCR products from different tissues revealed alternative splicing of exons 3 and 5, which results in the generation of four different mRNA isoforms. RNA extracted from tumor tissues contained more CPM mRNA than control tissue, suggesting an upregulation of CPM expression in tumors and raising the question of the role of this enzyme in cancer.