Endotoxemia is frequently associated clinically with disseminated intravascular coagulation (DIC); however, the mechanism of endotoxin action in vivo is unclear. Modulation of tissue factor (TF) and thrombomodulin (TM) expression on the endothelial surface may be relevant pathophysiologic mechanisms. Stimulation of human umbilical vein endothelial cells with endotoxin (1 ,ug/ml) increased surface TF activity from 1.52±0.84 to 11.89±8.12 mU/ml-106 cells at 6 h (n = 11) which returned to baseline by 24 h. Repeated stimulation at 24 h resulted in renewed TF expression. Endotoxin (1 ,tg/ml) also caused a decrease in TM expression to 55.0±6.4% of control levels at 24 h (n = 10) that remained depressed at 48 h. Both effects were dose and serum dependent. A temporary rise in TF expression accompanied by a sustained fall in TM expression comprise a shift in the hemostatic properties of the endothelium that would favor intravascular coagulation and may contribute to the pathogenesis of DIC in gram-negative septicemia.

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Our studies suggest that PAI-1 is the circulating inhibitor of fibrinolysis in the hemolytic uremic syndrome. Normalization of plasma PAI-1 levels (e.g., by peritoneal dialysis) is correlated with improvement in renal function. However, the possibility that increased plasma levels of PAI-1 are either causes or effects of the hemolytic uremic syndrome is not unequivocally established by these studies.

Two glycoforms of a secretable human thrombomodulin mutant [TMD1-105 and TMD1-75; Parkinson, Grinnell, Moore, Hoskins, Vlahos & Bang (1990) J. Biol. Chem. 265, 12602-12610] were expressed in human 293 cells and used to study the role of glycosylation in the functions of this endothelial-cell thrombin receptor. Carbohydrate content analysis and intrinsic labelling with [3H]glucosamine and [35S]sulphate showed that TMD1-105 contained a chondroitin sulphate whereas TMD1-75 did not. Other than chondroitin sulphate, the carbohydrate contents of the two glycoforms were identical, indicating similar glycosylation patterns at other O-linked and N-linked sites in the two glycoforms. The properties of TMD1-105 were converted into those of TMD1-75 by chondroitin ABC lyase digestion. Trypsin digestion of labelled TMD1-105 permitted isolation of two overlapping peptides that contained chondroitin sulphate, spanned the entire O-glycosylation domain and had O-glycosylation sites at Ser-492, Ser-498, Thr-500, Thr-504 and Thr-506. The chondroitin sulphate-attachment site was assigned to Ser-492 as this residue is conserved in mouse and bovine thrombomodulin and lies within a sequence Ser-Gly-Ser-492-Gly-Glu-Pro, which has strong similarity to chondroitin sulphate attachment sites in other proteoglycans. Five peptides with N-linked carbohydrate were also isolated and contained glycosylation sites in the lectin-like domain (Asn-47, Asn-115, Asn-116) and in the fourth (Asn-382) and fifth (Asn-409) epidermal growth factor domains. The role of N-linked and simple O-linked carbohydrates in the functions of human thrombomodulin remain unclear. The present studies demonstrate, however, that the presence of chondroitin sulphate in human thrombomodulin has profound effects on all of the anticoagulant properties of this important anticoagulant thrombin receptor.

Calcium plays a dual role in the activation of protein C: it inhibits protein C activation by a-thrombin, whereas it is required for protein C activation by the thrombomodulin-thrombin complex. Available information suggests that these calcium effects are mediated through calcium induced structural changes in protein C. In this paper, we demonstrate that substitution of Aspl67 (located in the activation peptide of human protein C, occupying position P3 relative to the peptide bond Argl69-Leul7O which is susceptible to hydrolysis by thrombin) by either Gly or Phe results in protein C derivatives which are characterized by an altered response to calcium. At 3 mM calcium, a-thrombin activated the derivatives 5-to 8-fold faster compared with the wild-type, an effect which was shown to be caused by a decreased inhibitory effect of calcium on the reaction. These same single amino acid substitutions enhanced the affinity of the thrombomodulin-thrombin complex for the substrate at 3 mM calcium 3-(Glysubstitution) to 6-(Phe-substitution) fold, either without influencing kc.t (Gly-substitution) or with a 2.5-fold decrease of keat. For both derivatives, the calcium concentrations resulting in half maximal inhibition of activation by ct-thrombin and in half maximal stimulation of activation by the thrombomodulin -thrombin complex increased from 0.3 mM to 0.6 mM. It is concluded that Aspl67 is involved in the calcium induced inhibition of protein C activation by thrombin. Moreover, our studies demonstrate that it is feasible to enhance the efficiency of enzymatic reactions by introducing point mutations in the substrate.

Thrombomodulin (TM) is an endothelial cell thrombin receptor that converts thrombin from a procoagulant to an anticoagulant enzyme. It has previously been shown that TM is expressed in both a high-M(r) form containing chondroitin sulphate and a low-M(r) form lacking this modification. Site-directed mutagenesis of a soluble human TM derivative (TMD1) was employed to determine the attachment site(s) of this functionally important oligosaccharide on the core protein. Although there are four serine residues within the Ser/Thr-rich domain of TMD1 that might support glycosaminoglycan assembly, our analysis demonstrates that the primary site of attachment is at Ser474, and evidence is presented for low levels of attachment at Ser472. It was possible to improve the overall degree of attachment by mutating Ser472 to glutamic acid (so as to conform Ser474 to the xylosyltransferase acceptor consensus acidic-Gly-Ser-Gly-acidic); however, a significant proportion (approx. 35%) of the total TM still lacked a glycosaminoglycan moiety. Mutants that possess a substitution for Ser474 show an increased mobility of their low-M(r) form on SDS/PAGE compared with native TMD1. Isolation and sequencing of a C-terminal peptide demonstrated that this serine is modified in the low-M(r) form of native TMD1. An apparent 'acceptor consensus overlap' at Ser474 suggests that the mechanism behind the glycosaminoglycan split of TM may involve a competition for substrate between xylosyltransferase and N-acetylgalactosaminyltransferase.

A new American kindred with amyloidosis was found by single-strand conformation polymorphism analysis to have a mutation in the fibrinogen A alpha chain gene. Affected members in this kindred have autosomal dominant amyloid nephropathy. DNA sequencing showed a single nucleotide deletion at the third base of codon 524 of the fibrinogen A alpha chain genes (4904delG) that resulted in a frame shift and premature termination of the protein at codon 548. Antiserum was produced to a portion of the abnormal peptide predicted by the DNA sequence and amyloid deposits were immuno-histologically proven to contain this abnormal peptide. Two of the propositus' 4 children were positive for the mutant fibrinogen A alpha chain gene by restriction fragment length polymorphism analysis based on polymerase chain reaction. These two mutant gene carriers now in the second decade of life show no clinical symptoms of amyloidosis as yet but have lower plasma fibrinogen concentrations when compared with their normal siblings. This the first description of a kindred with renal amyloidosis and low plasma fibrinogen and also the first report of amyloidosis caused by a frame shift mutation.

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