High Molecular Weight Kininogen Regulates Prekallikrein Assembly and Activation on Endothelial Cells: A Novel Mechanism for Contact Activation

Human plasma kallikrein: roles in coagulation, fibrinolysis, inflammation pathways, and beyond

Human plasma kallikrein (PKa) is obtained by activating its precursor, prekallikrein (PK), historically named the Fletcher factor. Human PKa and tissue kallikreins are serine proteases from the same family, having high- and low-molecular weight kininogens (HKs and LKs) as substrates, releasing bradykinin (Bk) and Lys-bradykinin (Lys-Bk), respectively. This review presents a brief history of human PKa with details and recent observations of its evolution among the vertebrate coagulation proteins, including the relations with Factor XI. We explored the role of Factor XII in activating the plasma kallikrein-kinin system (KKS), the mechanism of activity and control in the KKS, and the function of HK on contact activation proteins on cell membranes. The role of human PKa in cell biology regarding the contact system and KSS, particularly the endothelial cells, and neutrophils, in inflammatory processes and infectious diseases, was also approached. We examined the natural plasma protein inhibitors, including a detailed survey of human PKa inhibitors' development and their potential market.

Plasma prekallikrein: a risk marker for hypertension and nephropathy in type 1 diabetes

The relevance and significance of the plasma kallikrein/kinin system as a risk factor for the development of vascular complications in diabetic patients was explored in a cross-sectional study. We measured the circulating levels of plasma prekallikrein (PK) activity, factor XII, and high-molecular weight kininogen in the plasma of 636 type 1 diabetic patients from the Diabetes Control and Complications Trial/Epidemiology and Diabetes Intervention and Complications Study cohort. The findings demonstrated that type 1 diabetic patients with blood pressure > or =140/90 mmHg have increased PK levels compared with type 1 diabetic patients with blood pressure <140/90 (1.53 +/- 0.07 vs. 1.27 +/- 0.02 units/ml; P < 0.0001). Regression analysis also determined that plasma PK levels positively and significantly correlated with diastolic (DBP) and systolic blood pressures (SBP) as continuous variables (r = 0.17 and 0.18, respectively; P < 0.0001). In multivariate regression analysis, the semipartial r(2) value for PK was 2.93% for SBP and 2.92% for DBP (P < 0.0001). A positive correlation between plasma PK levels and the urinary albumin excretion rate (AER) was also observed (r = 0.16, P < 0.0001). In categorical analysis, patients with macroalbuminuria had a significantly higher level of plasma PK than normoalbuminuric patients (1.45 +/- 0.08 vs. 1.27 +/- 0.02 units/ml; P < 0.01), whereas microalbuminuric patients had an intermediate PK value (1.38 +/- 0.05 units/ml; P = NS). Among patients in the microalbuminuric subgroup, we observed a positive and independent correlation between PK and AER in univariate and multivariate regression analysis (r = 0.27, P < 0.03; n = 63). We concluded that in type 1 diabetes, 1) PK levels are elevated in association with increased blood pressure; 2) PK levels are independently correlated with AER and are categorically elevated in patients with macroalbuminuria; and 3) although the positive correlation between PK and AER within the subgroups of patients with microalbuminuria suggest that PK could be a marker for progressive nephropathy, longitudinal studies will be necessary to address this issue.

Different mechanisms define the antiadhesive function of high molecular weight kininogen in integrin- and urokinase receptor–dependent interactions

Proteolytic cleavage of single-chain high molecular weight kininogen (HK) by kallikrein releases the short-lived vasodilator bradykinin and leaves behind 2-chain high molecular weight kininogen (HKa) that has been previously reported to exert antiadhesive properties as well as to bind to the urokinase receptor (uPAR) on endothelial cells. In this study we defined the molecular mechanisms for the antiadhesive effects of HKa related to disruption of integrin- and uPAR-mediated cellular interactions. Vitronectin (VN) but not fibrinogen or fibronectin-dependent vβ3 integrin–mediated adhesion of endothelial cells was blocked by HKa or its isolated domain 5. In a purified system, HKa but not HK competed for the interaction of VN with vβ3 integrin, because HKa and the isolated domain 5 but not HK bound to both multimeric and native VN in a Zn2+-dependent manner. The interaction between HKa or domain 5 with VN was prevented by heparin, plasminogen activator inhibitor-1, and a recombinant glutathione-S-transferase (GST)-fusion peptide GST-VN (1-77) consisting of the amino terminal portion of VN (amino acids 1-77), but not by a cyclic arginyl-glycyl-aspartyl peptide, indicating that HKa interacts with the amino terminal portion of VN (“somatomedin B region”). Furthermore, we have confirmed that HKa but not HK bound to uPAR and to the truncated 2-domain form of uPAR lacking domain 1 in a Zn2+-dependent manner. Through these interactions, HKa or its recombinant His-Gly-Lys–rich domain 5 completely inhibited the uPAR-dependent adhesion of myelomonocytic U937 cells and uPAR-transfected BAF-3 cells to VN and thereby promoted cell detachment. By immunogold electron microscopy, both VN and HK/HKa were found to be colocalized in sections from human atherosclerotic coronary artery, indicating that the described interactions are likely to take place in vivo. Taken together, HK and HKa inhibit different VN-responsive adhesion receptor systems and may thereby influence endothelial cell- or leukocyte-related interactions in the vasculature, particularly under inflammatory conditions.