Inter-alpha-trypsin inhibitor: a plasma proteinase inhibitor with a unique chemical structure

Revelation of Proteomic Indicators for Colorectal Cancer in Initial Stages of Development

Background: Colorectal cancer (CRC) at a current clinical level is still hardly diagnosed, especially with regard to nascent tumors, which are typically asymptotic. Searching for reliable biomarkers of early diagnosis is an extremely essential task. Identification of specific post-translational modifications (PTM) may also significantly improve net benefits and tailor the process of CRC recognition. We examined depleted plasma samples obtained from 41 healthy volunteers and 28 patients with CRC at different stages to conduct comparative proteome-scaled analysis. The main goal of the study was to establish a constellation of protein markers in combination with their PTMs and semi-quantitative ratios that may support and realize the distinction of CRC until the disease has a poor clinical manifestation. Results: Proteomic analysis revealed 119 and 166 proteins for patients in stages I–II and III–IV, correspondingly. Plenty of proteins (44 proteins) reflected conditions of the immune response, lipid metabolism, and response to stress, but only a small portion of them were significant (p < 0.01) for distinguishing stages I–II of CRC. Among them, some cytokines (Clusterin (CLU), C4b-binding protein (C4BP), and CD59 glycoprotein (CD59), etc.) were the most prominent and the lectin pathway was specifically enhanced in patients with CRC. Significant alterations in Inter-alpha-trypsin inhibitor heavy chains (ITIH1, ITIH2, ITIH3, and ITIH4) levels were also observed due to their implication in tumor growth and the malignancy process. Other markers (Alpha-1-acid glycoprotein 2 (ORM2), Alpha-1B-glycoprotein (A1BG), Haptoglobin (HP), and Leucine-rich alpha-2-glycoprotein (LRG1), etc.) were found to create an ambiguous core involved in cancer development but also to exactly promote tumor progression in the early stages. Additionally, we identified post-translational modifications, which according to the literature are associated with the development of colorectal cancer, including kininogen 1 protein (T327-p), alpha-2-HS-glycoprotein (S138-p) and newly identified PTMs, i.e., vitamin D-binding protein (K75-ac and K370-ac) and plasma protease C1 inhibitor (Y294-p), which may also contribute and negatively impact on CRC progression. Conclusions: The contribution of cytokines and proteins of the extracellular matrix is the most significant factor in CRC development in the early stages. This can be concluded since tumor growth is tightly associated with chronic aseptic inflammation and concatenated malignancy related to loss of extracellular matrix stability. Due attention should be paid to Apolipoprotein E (APOE), Apolipoprotein C1 (APOC1), and Apolipoprotein B-100 (APOB) because of their impact on the malfunction of DNA repair and their capability to regulate mTOR and PI3K pathways. The contribution of the observed PTMs is still equivocal, but a significant decrease in the likelihood between modified and native proteins was not detected confidently.

Diversity in the degree of sulfation and chain length of the glycosaminoglycan moiety of urinary trypsin inhibitor isomers

Five isomers with different electric charge were fractionated from human urinary trypsin inhibitor (UTI) by anion exchange HPLC. Intact low-sulfated chondroitin 4-sulfate chains from the isomers were analyzed by HPLC and mass spectrometry. Unsaturated disaccharide composition analysis of the chondroitin sulfate chain revealed that the five isomers differ in the numbers of 4-sulfated disaccharide units. Intriguingly, we detected the presence of multiple novel isomers with different numbers of non-sulfated disaccharide units even in the same charge isomer fraction. Our results demonstrate that UTI can vary in terms of both the degree of sulfation and the length of the low-sulfated chondroitin 4-sulfate chain.

TSG-6 and calcium ions are essential for the coupling of inter-alpha-trypsin inhibitor to hyaluronan in human synovial fluid

OBJECTIVE

To investigate the role of tumor necrosis factor stimulated gene 6 (TSG-6) and metal ions in the coupling of inter-alpha-trypsin inhibitor (ITI) to hyaluronan in human synovial fluid.

DESIGN

The concentration of ITI heavy chains bound to hyaluronan was determined by a two-step electrophoretic technique. Synovial fluid, TSG-6 depleted synovial fluid and metal chelated synovial fluid were tested for their ability to support the coupling of ITI heavy chains to hyaluronan.

RESULTS

When synovial fluid was mixed with an ITI-source (serum or purified ITI), coupling of ITI heavy chains to hyaluronan took place. TSG-6 immunodepleated synovial fluid lost the coupling activity, but addition of recombinant TSG-6 restored the activity. EDTA inhibited the coupling activity, but combinations of the metal-ion chelators Mg-EGTA and Ca-EGTA demonstrated, that Ca++ is essential for the coupling of ITI heavy chains to hyaluronan.

CONCLUSIONS

Tumor necrosis factor stimulated gene 6 (TSG-6) and calcium ions are both essential for the coupling of inter-alpha-trypsin inhibitor to hyaluronan in human synovial fluid.

Bikunin present in human peritoneal fluid is in part derived from the interaction of serum with peritoneal mesothelial cells

We recently reported that peritoneal fluid mainly contains two proteoglycans; one is the interstitial proteoglycan referred to as decorin, and the other an uncharacterized small chondroitin sulfate proteoglycan. In the present study, we have used a two-step process to isolate the small chondroitin sulfate proteoglycan free of decorin. The purified molecule ran as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with apparent molecular mass 50 kd made up of a chondroitin-4-sulfate glycosaminoglycan chain and a 30-kd core protein. NH2-terminal analysis of the core protein showed significant sequence homology with bikunin, a component of the human inter-alpha-trypsin inhibitor (IalphaI) family. A Western blot analysis using anti-human inter-alpha-trypsin inhibitor confirmed the identity of the small chondroitin sulfate proteoglycan as bikunin, and a trypsin inhibitor counterstain assay confirmed its anti-trypsin activity. Examination of serum from patients receiving continuous peritoneal dialysis suggests that free bikunin in peritoneal fluid may be the result of leakage of serum proteins into the peritoneum. Our findings further show that the interaction of serum with peritoneal mesothelial cells offers a new and novel explanation for the presence of bikunin in peritoneal fluid.

The serine proteinase inhibitory proteins of the chondrodystrophoid (beagle) and non-chondrodystrophoid (greyhound) canine intervertebral disc

Trypsin inhibitory proteins of low buoyant density (p < or = 1.35 g/mL) fractions were prepared by CsCl density gradient ultracentrifugation of 4 M guanidinium hydrochloride extracts of lumbar beagle and greyhound annulus fibrosus and nucleus pulposus from animals aged 1 to 6 years. Affinity blotting with biotinylated trypsin was used to identify active trypsin inhibitory protein species; these species were also identified immunologically by Western blotting using antibodies against bovine pancreatic trypsin inhibitor (BPTI), and human inter-alpha-trypsin inhibitor (ITI). None of the trypsin inhibitory species evident in Western blots were reactive with anti-human alpha1-proteinase inhibitor (alpha-1-PI), alpha2-macroglobulin or secretory leucocyte proteinase inhibitor. The greyhound intervertebral disc samples generally had higher levels of active trypsin inhibitor species per unit weight of tissue extracted, and a more extensive range of inhibitor species. Inhibitor species of 30, 32, 34 kDa were identified in both beagle and greyhound intervertebral disc samples; these species were generally most prominent in the annulus fibrosus samples. In contrast, the nucleus pulposus samples contained relatively large trypsin inhibitor species; the anti-BPTI detected an inhibitor species of approximately 85-90 kDa; anti-ITI detected species of 120-250 kDa; biotinylated trypsin detected species of 60-110 kDa. A small molecular mass trypsin inhibitor species of 6 kDa, which was of similar mobility to BPTI, was also detected in annulus fibrosus samples; however, this species did not react with anti-BPTI.

Bikunin and alpha 1-microglobulin in human zona pellucida and connective tissue

The occurrence of bikunin and alpha 1-microglobulin was investigated in human ovary and Fallopian tubes. Bikunin and alpha 1-microglobulin are transcribed in the liver from a common gene. Bikunin immunoreactivity was detected in the zona pellucida. A positive reaction for bikunin was also observed in connective tissue of the oviduct. In addition, mast cells showed a more intense positive reaction than the surrounding connective tissue. Specific displaceable alpha 1-microglobulin immunoreactivity was revealed in the zona pellucida. The data suggest that bikunin and alpha 1-microglobulin are trapped in the zona pellucida.

In vivo binding of human inter-alpha-trypsin inhibitor free heavy chains to hyaluronic acid

In vivo binding of human inter-alpha-trypsin inhibitor to hyaluronate was investigated by immunoelectrophoretic techniques. Pathological synovial fluids and follicular fluids both contain high concentrations of soluble hyaluronate. Heavy chain epitopes of inter-alpha-trypsin inhibitor were firmly associated with the hyaluronate in synovial fluid and follicular fluid. The hyaluronate-bound inter-alpha-trypsin inhibitor epitopes did not cross-react immunologically with bikunin. Several hyaluronate-bound inter-alpha-trypsin inhibitor fragments with molecular masses in the range 120,000-30,000 Da were demonstrated by immunoblotting. Heavy chain 1 of inter-alpha-trypsin inhibitor was shown to associate with hyaluronate by amino acid sequence analysis of isolated hyaluronate-bound proteins. These data indicate that in vivo metabolism of inter-alpha-trypsin inhibitor takes place in pathological synovial fluid and in ovarian follicular fluid shortly before ovulation.

Bikunin in rat plasma, lymph and bile

Bikunin is a protease inhibitor consisting of a 16 kDa polypeptide and an 8 kDa chondroitin sulphate chain which has an apparent molecular mass of 60-70 kDa upon gel filtration. It is synthesized by hepatocytes and occurs in plasma, both in free form, and in complex with other polypeptides--mainly as the 180 kDa protein inter-alpha-inhibitor. Bikunin binds to proteases less avidly than other plasma inhibitors, making its role in the blood unclear. However, some observations indicate that bikunin has important functions outside the blood system. To assess its capacity to reach extravascular spaces, we have determined the total concentration of bikunin in plasma (0.17 mg/ml), lymph (31 micrograms/ml) and bile (0.2 microgram/ml). Quantitation after removal of complexed bikunin (inter-alpha-inhibitor) by acid precipitation showed that the concentration of free bikunin in those fluids was 3, 1.4 and 0.05 micrograms/ml, respectively. These values yield a lymph/plasma ratio of free bikunin of 0.5, which is higher than expected for a protein of the hydrodynamic size and charge of bikunin. The bile/plasma ratio (0.02), however, is similar to that of other proteins of comparable size. The corresponding values for inter-alpha-inhibitor, 0.16 and 0.001, respectively, indicate that its capacity to pass through the vascular endothelium is relatively high whereas transfer to bile is restricted. Furthermore, we have found that in a perfusate of an isolated rat liver, the ratio of free to complexed bikunin was 30-40 times higher than in plasma, consistent with previous observations showing that free bikunin is cleared from the blood stream much more rapidly than inter-alpha-inhibitor.

Function of proteoglycans in the extracellular matrix

Proteoglycans are glycosylated proteins which have covalently attached highly anionic glycosaminoglycans. Many forms of proteoglycans are present in virtually all extracellular matrices of connective tissues. The major biological function of proteoglycans derives from the physicochemical characteristics of the glycosaminoglycan component of the molecule, which provides hydration and swelling pressure to the tissue enabling it to withstand compressional forces. This function is best illustrated by the most abundant proteoglycan in cartilage tissues, aggrecan. During the past decade, diverse species of proteoglycans have been identified in many connective tissues, on cell surfaces and in intracellular compartments. These proteoglycans have distinct biological functions apart from their hydrodynamic functions, and their involvement in many aspects of cell and tissue activities has been demonstrated. For example, decorin, which is widely distributed in many connective tissues, may have functions in regulating collagen fibril formation and in modifying the activity of transforming growth factor-beta; perlecan, the major heparan sulfate proteoglycan in the glomerular basement membrane, may play an important role as the major anionic site responsible for the charge selectivity in glomerular filtration. Specific interactions between proteoglycans (through both their glycosaminoglycan and core protein components) and macromolecules in the extracellular matrix are the key factors in the functions of proteoglycans. Exciting biological functions of proteoglycans are now gradually emerging.