Modification of the tandem reactive centres of human inter-alpha-trypsin inhibitor with butanedione and cis-dichlorodiammineplatinum(II)

TNF-α-induced self expression in human lung endothelial cells is inhibited by native and oxidized α1-antitrypsin

Endothelial cells are among the main physiological targets of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). In endothelial cells TNF-alpha elicits a broad spectrum of biological effects including differentiation, proliferation and apoptosis. alpha1-antitrypsin (AAT), an endogenous inhibitor of serine proteases plays a vital role in protecting host tissue from proteolytic injury at sites of inflammation. Recently, it has been shown that AAT can be internalized by pulmonary endothelial cells, raising speculation that it may modulate endothelial cell function in addition to suppressing protease activity. Using Affymetrix microarray technology, real time PCR and ELISA methods we have investigated the effects of AAT on un-stimulated and TNF-alpha stimulated human primary lung microvascular endothelial cell gene expression and protein secretion. We find that AAT and TNF-alpha generally induced expression of distinct gene families with AAT exhibiting little activity in terms of inflammatory gene expression. Approximately 25% of genes up regulated by TNF-alpha were inhibited by co-administration of AAT including TNF-alpha-induced self expression. Surprisingly, the effects of AAT on TNF-alpha-induced self expression was inhibited equally well by oxidized AAT, a modified form of AAT, which lacks serine protease inhibitor activity. Overall, the pattern of gene expression regulated by native and oxidized AAT was similar with neither inducing pro-inflammatory gene expression. These findings suggest that inhibitory effects of native and oxidized forms of AAT on TNF-alpha stimulated gene expression may play an important role in limiting the uncontrolled endothelial cell activation and vascular injury in inflammatory disease.

Bikunin--not just a plasma proteinase inhibitor

Bikunin is a plasma proteinase inhibitor that has received little attention in the past, probably because its activity towards various proteinases was found to be relatively weak in early work. It was recently discovered, however, that bikunin effectively inhibits a proteinase that seems to be involved in the metastasis of tumour cells--cell surface plasmin--and that a fragment of bikunin inhibits two proteinases of the coagulation pathway--factor Xa and kallikrein. Furthermore, it has been found that bikunin has other properties, such as the ability to modulate cell growth and to block cellular calcium uptake. Most of the bikunin in the blood occurs as a covalently linked subunit of the proteins pre- and inter-alpha-inhibitor. In this form bikunin lacks some of its known activities, and there is evidence that its release by partial proteolytic degradation may function as a regulatory mechanism. Although the physiological function of bikunin still remains to be established, current data suggest that this protein plays a role in inflammation. Further studies could therefore lead to results of therapeutical value.

Intracellular proteolytic processing of the heavy chain of rat pre-alpha-inhibitor. The COOH-terminal propeptide is required for coupling to bikunin

Pre-alpha-inhibitor is a serum protein consisting of two polypeptides named bikunin and heavy chain 3 (H3). Both polypeptides are synthesized in hepatocytes and while passing through the Golgi complex, bikunin, which carries a chondroitin sulfate chain, becomes covalently linked to the COOH-terminal amino acid residue of H3 via its polysaccharide. Immediately prior to this reaction, a COOH-terminal propeptide of 33 kDa is cleaved off from the heavy chain. Using COS-1 cells transfected with rat H3, we found that in the absence of bikunin, the cleaved propeptide remained bound to the heavy chain and that H3 lacking the propeptide sequence did not become linked to coexpressed bikunin. Sequencing of H3 secreted from COS-1 cells showed that part of the molecules had a 12-amino acid residue long NH2-terminal propeptide. Cleavage of this propeptide, which occurred in the endoplasmic reticulum, was found to require basic amino acid residues at P1, P2, and P6 suggesting that it is mediated by a Golgi enzyme in transit. Deletion of the NH2-terminal propeptide or blocking of its release affected neither transport nor coupling of the heavy chain to bikunin.

Intracellular coupling of bikunin and the heavy chain of rat pre-alpha-inhibitor in COS-1 cells

Pre-alpha-inhibitor is a serum protein consisting of two polypeptides: bikunin of 16 kDa, which carries an 8 kDa chondroitin sulphate chain, and heavy chain 3 (H3) of 74 kDa. The two polypeptides are linked through an ester bond between an internal N-acetylgalactosamine residue of the chondroitin sulphate chain and the C-terminal aspartic acid residue of H3. Both bikunin and H3 are synthesized by hepatocytes and become linked as they pass through the Golgi complex. H3 is synthesized with both N- and C-terminal extensions which are released during intracellular transport. To be able to analyse the assembly of pre-alpha-inhibitor in detail, we have cloned and sequenced the cDNA of rat H3. Upon expression of the protein in COS-1 cells, both propeptides were found to be released. Furthermore, co-expression of H3 and bikunin resulted in the two polypeptides becoming coupled, indicating that cells other than hepatocytes may have the capacity to form chondroitin sulphate-containing links.

Increase of bikunin and alpha1-microglobulin concentrations in urine of rats during pregnancy is due to decreased tubular reabsorption

Bikunin and alpha1-microglobulin are two plasma proteins of about 25 kDa which are made in the liver from a common precursor. The concentration of bikunin in human urine has been shown to increase several fold during various conditions of stress. The mechanism behind this increase is unknown. We have studied pregnant rats and found that the bikunin and alpha1-microglobulin levels in their urine increased 3-fold towards the end of the pregnancy, whereas those of albumin and orosomucoid did not. There were no significant changes in either the bikunin/alpha1-microglobulin mRNA level or the concentrations of the two proteins in serum. These findings imply that the synthesis and the clearance rates of bikunin and alpha1-microglobulin are normal during pregnancy but that the tubular reabsorption of these proteins is decreased.

High glomerular permeability of bikunin despite similarity in charge and hydrodynamic size to serum albumin

Bikunin is a chondroitin-sulphate containing serum protein with a Stokes-Einstein radius and a negative net charge close to those of serum albumin. The plasma half life of bikunin is about 10 minutes, and approximately half of its clearance occurs in the kidneys. The quantitative role of glomerular filtration in the renal clearance of this protein has not been determined. To assess the glomerular permeability of bikunin we used isolated rat kidneys that were perfused with an albumin solution. The metabolic activities of the tubuli were inhibited by low temperature (8 degrees C). The clearances of radiolabeled bikunin and albumin were repeatedly determined under identical conditions. The fractional clearance of bikunin was found to be 80 times higher than that of albumin: 15% +/- 1% versus 0.18% +/- 0.02%. This value for bikunin can fully account for its renal clearance in vivo. It has previously been shown that uncharged flexible solutes, such as dextrans, have higher renal clearances than globular molecules with similar radii. The high glomerular permeability of bikunin is therefore probably due to its elongated and flexible configuration. Moreover, the observed clearance value of the anionic molecule bikunin is close to that of a neutral flexible dextran of similar size, indicating that the charge of bikunin is of little importance for its glomerular permeability.

Isolation, characterization, and properties of a trypsin-chymotrypsin inhibitor from amaranth seeds

A trypsin-chymotrypsin inhibitor was isolated from the seeds of amaranth--a highly nutritious protein source. The purification of the inhibitor (AmI) was carried out by affinity chromatography on trypsin-Sepharose and by HPLC. AmI is a single-chain protein of 8 kD, as determined by electrophoresis on SDS-polyacrylamide gels and by gel exclusion on Sephadex G-50 column. It is stable at neutral and alkaline pH and is relatively thermostable. AmI inhibits trypsin and chymotrypsin from the digestive system of insects such as Tribolium castaneum and Locusta migratoria, supporting the hypothesis that inhibitors may have evolved as defense mechanisms of seeds against insects. AmI lost its inhibitory activities when submitted to limited proteolysis with trypsin, while limited proteolysis with chymotrypsin had almost no effect. The partial amino acid sequence of 45 amino acids from the amino terminus of AmI differs significantly from the known sequences of legume-seed and cereal-grain protease inhibitor families. Differences in the chemistry at the inhibitory site(s) and in the amino acid sequence of AmI in comparison to that of other cereal and legume inhibitors suggest that AmI is a member of a new family of serine protease inhibitors. AmI was found to inhibit the anchorage-independent growth of MCF-7 breast cancer cells, suggesting that AmI may have anticarcinogenic activity.

Plasma clearance of rat bikunin: evidence for receptor-mediated uptake

Bikunin is a chondroitin sulphate-containing protease inhibitor with a molecular mass of 25 kDa. It is secreted into the blood by hepatocytes, and recent observations indicate that it may have an extravascular function. Here we have studied the plasma clearance of bikunin in rats and mice. On intravenous injection, radiolabelled bikunin was found to have a half-life of 10 min; in rats with ligated renal arteries, the clearance time was twice as long, implying that the kidneys account for half the uptake. As judged by gel filtration, the size of bikunin is similar to that of albumin. Autoradiographic analysis of kidneys removed 2 min after the injection of radiolabelled bikunin indicated that, despite its size, bikunin is cleared by glomerular filtration. On ligation of the renal arteries, the plasma concentration of bikunin increased linearly to at least four times normal. This finding shows that the non-renal uptake system is saturated and therefore presumably receptor-mediated. Most of the non-renal uptake of injected bikunin was found to occur in non-visceral tissues such as the skin. Analysis of skin samples by autoradiography after injection of radiolabelled bikunin suggested that bikunin had been transferred from the plasma to the interstitial space.

Novel factor Xa and plasma kallikrein inhibitory-activities of the second Kunitz-type inhibitory domain of urinary trypsin inhibitor

Urinary trypsin inhibitor is a glycoprotein with a structure in which two Kunitz-type inhibitory domains are linked in a row. We isolated two genes encoding the 70 amino acid sequence from the 78th amino acid (Thr) to the C-terminal and the 68 amino acid sequence from the 80th (Ala) to the C-terminal of human urinary trypsin inhibitor, both which correspond to the second Kunitz-type inhibitory domain, and then constructed expression plasmids by ligating it to the E. coli alkaline phosphatase signal peptide gene. These plasmids under the control of the tryptophan promoter expressed the second domain in E. coli strain JE5505 which lacks the membrane lipoprotein. The recombinant second domain purified from the culture supernatant of the transformant inhibited trypsin, plasmin, leukocyte elastase and chymotrypsin which are known to be inhibited by urinary trypsin inhibitor. In addition it inhibited blood coagulation factor Xa and plasma kallikrein in a concentration dependent and competitive manner, and significantly prolonged the plasma-based activated partial thromboplastin time (APTT). The truncated natural counterpart obtained by a limited degradation of human urinary trypsin inhibitor also revealed the identical inhibitory activities.