A low-molecular-mass Kazal-type protease inhibitor isolated from rat hepatocytes is identical to rat pancreatic secretory trypsin inhibitor II. Purification and amino acid sequence

Trypsin/acrosin inhibitor activity of rat and guinea pig caltrin proteins. Structural and functional studies

Dramatic inhibition of trypsin activity by rat caltrin and guinea pig caltrin I was spectrophotometrically demonstrated using the artificial substrate benzoylarginyl ethyl ester. Approximately 6% and 21% of residual proteolytic activity was recorded after preincubating the enzyme with 0.22 and 0.27 microM rat caltrin and guinea pig caltrin I, respectively. Reduction and carboxymethylation of the cysteine residues abolished the inhibitor activity of both caltrin proteins. Rat caltrin and guinea pig caltrin I show structural homology with secretory trypsin/acrosin inhibitor proteins isolated from boar and human seminal plasma and mouse seminal vesicle secretion and share a fragment of 13 amino acids of almost identical sequence (DPVCGTDGH/K/ITYG/AN), which is also present in the structure of Kazal-type trypsin inhibitor proteins from different mammalian tissues. Bovine, mouse, and guinea pig caltrin II, three caltrin proteins that have no structural homology with rat caltrin or guinea pig caltrin I, lack trypsin inhibitor activity. Rat caltrin, guinea pig caltrin I, and the mouse seminal vesicle trypsin inhibitor protein P12, which also inhibits Ca(2+) uptake into epididymal spermatozoa (mouse caltrin I), bound specifically to the sperm head, on the acrosomal region, as detected by indirect immunofluorescence. They also inhibited the acrosin activity in the gelatin film assay. Caltrin I may play an important role in the control of sperm functions such as Ca(2+) influx in the acrosome reaction and activation of acrosin and other serine-proteases at the proper site and proper time to ensure successful fertilization.

Purification of two low-molecular-mass serine proteinase inhibitors from chicken liver

Two serine proteinase inhibitors, designated clTI-1 and clTI-2 were purified from livers of chickens to apparent homogeneity by a combination of ethanol-acetone fractionation, gel filtration and ion-exchange chromatography on CM-cellulose and Mono S columns. The inhibitor clTI-1 is a single polypeptide chain, low-molecular-mass protein (Mr about 6200), very stable to heat and ethanol. It inhibits chicken, porcine and bovine trypsins as well as human plasmin. The second protein, clTI-2 of Mr 17,000 was shown to be a very effective inhibitor of both trypsins and human cathepsin G. Since both inhibitors are sensitive to arginine modification with phenylglyoxal it is assumed that this amino acid residue is present at the P1 position of the reactive site peptide bond. The N-terminal amino acid sequence of 28 residues of clTI-2 (SVDVSKYPSTVSKDGRTLVACPRILSPV) revealed a high homology of this protein to the third domain of the chicken ovoinhibitor, whereas, the clTI-1 (APPAAEKYYSLPPGAPRYYSPVV) has some sequence identity to a fragment of the human inter-alpha-trypsin inhibitor.

Cloning of a new Kunitz-type protease inhibitor with a putative transmembrane domain overexpressed in pancreatic cancer

In a previous large scale screen for differentially expressed genes in pancreatic cancer, we identified a gene highly overexpressed in cancer encoding a novel putative transmembrane protein with two Kunitz-type serine protease inhibitor domains. The identified gene named kop (Kunitz domain containing protein overexpressed in pancreatic cancer) was assigned to chromosome 19 in the region 19q13.1. Kop was detected at high levels in pancreatic cancer cell lines and was overexpressed in pancreatic cancer tissues as compared to both, normal pancreas and chronic pancreatitis tissues. Being a member of the Kunitz-type serine protease inhibitor family, this new gene may participate in tumour cell invasion and metastasis and in the development of the marked desmoplastic reaction typical for human pancreatic cancer tissues. In this context, the fact that kop has a putative transmembrane domain may have functional implications of particular interest.

Dietary modulation of the mRNA stability of trypsin isozymes and the two forms of secretory trypsin inhibitor in the rat pancreas

The stability of the mRNAs encoding pancreatic trypsin isozymes, namely the cationic form and the two anionic forms I and II, as well as that of the secretory trypsin inhibitors I and II, were studied in rats fed on either a high-protein diet, or a protein-free diet compared with a standard diet for a 10-day period. Either immediately or 3 h and 6 h after injecting the transcription inhibitor, actinomycin D, the mRNA levels were quantified by performing dot-blot hybridization with specific oligonucleotide probes. Under high-protein dietary conditions, the stability of the mRNAs coding for anionic trypsin II and cationic trypsin showed no change, whereas that of anionic trypsin I and the two forms of secretory trypsin inhibitor were affected. The mRNA half-life of anionic trypsin I and trypsin inhibitor II increased, in sharp contrast with that of trypsin inhibitor I, which decreased. When rats were fed on a protein-free diet, the stabilities of both anionic trypsin forms and trypsin inhibitor I increased, whereas that of trypsin inhibitor II decreased and that of cationic trypsin remained unchanged. The present results show the existence of differences in the mechanisms whereby gene expression of trypsin isozymes and secretory trypsin inhibitors is regulated, although they are synthesized in parallel in the pancreatic acinar cell and stored in zymogen granules before being secreted into the intestinal lumen.

Absence of trypsinogen autoactivation and immunolocalization of pancreatic secretory trypsin inhibitor in acinar cells in vitro

To establish the significance of the addition of trypsin inhibitors to pancreatic acinar cells maintained in vitro, cells were cultured in the presence or absence of soybean trypsin inhibitor. Both cultures exhibited similar growth pattern, ultrastructural appearance, as well as secretory properties. Moreover, there was no evidence of trypsinogen activation in the culture medium. Using the immunocytochemical approach, pancreatic secretory trypsin inhibitor antigenic sites were revealed with specific polyclonal and monoclonal antibodies. The results obtained demonstrated that this trypsin inhibitor is in fact a typical pancreatic secretory protein being processed through the endoplasmic reticulum-Golgi-granule secretory pathway of the acinar cells in rat and human tissues. While the polyclonal antibody yield labelings of increasing intensities along the secretory pathway, the monoclonal one probably due to the molecular nature of its specific antigenic determinant, gave higher labelings in the endoplasmic reticulum. In conclusion the present study has shown that pancreatic acinar cells secrete a specific pancreatic trypsin inhibitor which most probably is involved in the mechanism to prevent trypsinogen activation.

Pancreatic secretory trypsin inhibitor (PSTI) isolated from pig intestine. Influence on insulin and somatostatin release

Upon investigation of pig intestinal peptides for effects on the release of endocrine hormones from the isolated perfused rat pancreas, we reported earlier that glucose-stimulated insulin release was inhibited by PEC-60, a peptide with marked sequence similarity to PSTI (pancreatic secretory trypsin inhibitor). Continuing this study we found a polypeptide, which inhibited glucose-induced insulin release but enhanced glucose-induced somatostatin secretion. Determination of the amino acid sequence of this polypeptide revealed that it is identical to that of PSTI. Thus, PSTI modulates islet hormone release.

Biology and function of tumor-associated trypsin inhibitor, TATI

Tumor-associated trypsin inhibitor (TATI) is a 6,000 Daltons peptide, which is synthesized by several tumors and cell lines. TATI is identical to pancreatic secretory trypsin inhibitor (PSTI). This peptide is also produced by the mucosa of the gastrointestinal tract, where it is thought to protect the mucosal cells from proteolytic breakdown. Elevated serum and urine levels of TATI occur in connection with many types of cancer, especially mucinous ovarian cancer. Elevated levels may also occur in nonmalignant diseases, e.g. in pancreatitis, severe infections and tissue destruction. Thus TATI may behave as an acute phase reactant. Tumors producing TATI often express tumor-associated trypsinogen. Elevation of TATI in cancer and pancreatic disease is therefore associated with expression of trypsin, but such a connection has not been demonstrated in inflammatory disease. TATI can inhibit trypsin-mediated degradation of extracellular matrix by tumor cells. Therefore its role may be to control the activation of tumor-associated trypsinogen. TATI has also been shown to possess growth factor activity in vitro, but it is not known whether this is a physiological function.