Differential regulation of trypsinogen mRNA translation: full-length mRNA sequences encoding two oppositely charged trypsinogen isoenzymes in the dog pancreas

Evolutionary expansion of polyaspartate motif in the activation peptide of mouse cationic trypsinogen limits autoactivation and protects against pancreatitis

The activation peptide of mammalian trypsinogens typically contains a tetra-aspartate motif (positions P2-P5 in Schechter-Berger numbering) that inhibits autoactivation and facilitates activation by enteropeptidase. This evolutionary mechanism protects the pancreas from premature trypsinogen activation while allowing physiological activation in the gut lumen. Inborn mutations that disrupt the tetra-aspartate motif cause hereditary pancreatitis in humans. A subset of trypsinogen paralogs, including the mouse cationic trypsinogen (isoform T7), harbor an extended penta-aspartate motif (P2-P6) in their activation peptide. Here, we demonstrate that deletion of the extra P6 aspartate residue (D23del) increased the autoactivation of T7 trypsinogen threefold. Mutagenesis of the P6 position in wild-type T7 trypsinogen revealed that bulky hydrophobic side chains are preferred for maximal autoactivation, and deletion-induced shift of the P7 Leu to P6 explains the autoactivation increase in the D23del mutant. Accordingly, removal of the P6 Leu by NH₂-terminal truncation with chymotrypsin C reduced the autoactivation of the D23del mutant. Homozygous T7D23del mice carrying the D23del mutation did not develop spontaneous pancreatitis and severity of cerulein-induced acute pancreatitis was comparable with that of C57BL/6N controls. However, sustained stimulation with cerulein resulted in markedly increased histological damage in T7D23del mice relative to C57BL/6N mice. Furthermore, when the T7D23del allele was crossed to a chymotrypsin-deficient background, the double-mutant mice developed spontaneous pancreatitis at an early age. Taken together, the observations argue that evolutionary expansion of the polyaspartate motif in mouse cationic trypsinogen contributes to the natural defenses against pancreatitis and validate the role of the P6 position in autoactivation control of mammalian trypsinogens.NEW & NOTEWORTHY Unwanted autoactivation of the digestive protease trypsinogen can result in pancreatitis. The trypsinogen activation peptide contains a polyaspartate motif that suppresses autoactivation. This study demonstrates that evolutionary expansion of these aspartate residues in mouse cationic trypsinogen further inhibits autoactivation and enhances protection against pancreatitis.

Validation of a radioimmunoassay of serum trypsin-like immunoreactivity in ferrets

Measurement of serum trypsin-like immunoreactivity (TLI) is used to assess exocrine pancreatic function in dogs and cats. Ferrets ( Mustela putorius furo) serve as valuable animal models for human diseases such as cystic fibrosis and other pulmonary diseases, and may be a useful model of other diseases including pancreatitis. We developed and analytically validated a competitive radioimmunoassay (RIA) for measurement of TLI in ferret serum by determination of analytical sensitivity, assay linearity, accuracy of spiking recovery, precision, and reproducibility. Analytical sensitivity of the assay was 0.55 μg/L. Observed-to-expected (O/E) ratio for dilutional parallelism was 90.2-127.9% (mean: 108.1 ± 11.9%). The O/E ratio for spiking recovery was 94.5-113.0% (mean: 103.9 ± 7.2%). The intra- and inter-assay coefficients of variation (CVs) were 2.7-5.7% and 3.5-8.2%, respectively. The reference interval (RI) for serum TLI derived from 31 healthy ferrets was 28-115 μg/L; the 90% confidence interval for the lower and upper limits of the RI were 10.0-32.1 μg/L and 103-126 μg/L, respectively. This TLI RIA is analytically sensitive, sufficiently linear, accurate, precise, and reproducible for the measurement of TLI in ferret serum samples.

A trypsin homolog in amphioxus: expression, enzymatic activity and evolution

Trypsin has been documented in a variety of species including both vertebrates and invertebrates, but little is known about it in amphioxus, a model organism for insights into the origin and evolution of vertebrates. Here we identified a trypsin gene in Branchiostoma japonicum. The cDNA was 978 bp long with an ORF encoding a deduced protein of 272 amino acids. The deduced protein had an N-terminal signal peptide of 15 amino acids, a 16 activation peptide with the typical cleavage site Arg/Ile, a Tryp_SPc domain with the catalytic triad His(72)-Asp(118)-Ser(215) and the S1 substrate binding residue Asp(209), which are all characteristic of trypsinogens. The recombinant trypsin protein was able to hydrolyse the trypsin prototypic substrate BAEE, which was inhibited by the trypsin-specific inhibitor soybean trypsin inhibitor. Both northern blotting and tissue-section in situ hybridization demonstrated that trypsin gene was expressed in a tissue-specific manner, with most abundant levels in the hepatic caecum, mid-gut and ovary. And the whole mount in situ hybridization showed that it began to express in the middle third of the full-length primitive gut in 2-day larvae, where the hepatic caecum will form later during development. Phylogenetic analysis indicated that both amphioxus and ascidian trypsins are more closer to each other than to vertebrate trypsins, suggesting a continuous evolutionary divergence of vertebrate trypsins after split from protochordate/vertebrate common ancestor.

Isolation and characterization of the chicken trypsinogen gene family

Based on genomic Southern hybridizations and cDNA sequence analyses, the chicken trypsinogen gene family can be divided into two multi-member subfamilies, a six-member trypsinogen I subfamily which encodes the cationic trypsin isoenzymes and a three-member trypsinogen II subfamily which encodes the anionic trypsin isoenzymes. The chicken cDNA and genomic clones containing these two subfamilies were isolated and characterized by DNA sequence analysis. The results indicated that the chicken trypsinogen genes encoded a signal peptide of 15 to 16 amino acid residues, an activation peptide of 9 to 10 residues and a trypsin of 223 amino acid residues. The chicken trypsinogens contain all the common catalytic and structural features for trypsins, including the catalytic triad His, Asp and Ser and the six disulphide bonds. The trypsinogen I and II subfamilies share approximately 70% sequence identity at the nucleotide and amino acid level. The sequence comparison among chicken trypsinogen subfamily members and trypsin sequences from other species suggested that the chicken trypsinogen genes may have evolved in coincidental or concerted fashion.

Nucleotide sequence of a novel arylesterase gene from Vibro mimicus and characterization of the enzyme expressed in Escherichia coli

A gene coding for an arylesterase of Vibrio mimicus was cloned. Sequence determination reveals that the esterase gene has an open reading frame of 600 nucleotides which encodes a protein of M(r) 22,300. The deduced amino acid sequence contain a pentapeptide GDSLS (residues 27-31), which was also found in the phospholipid-cholesterol acyltransferase from Aeromonas hydrophila. Substitution of Ser-29 by alanine or cysteine in the cloned gene abolished the esterase activity in the tributyrin plate assay. On the other hand, the activity was not lost when Ser-31 was changed to alanine. The cloned gene was expressed in Escherichia coli, and the protein purified by a four-step procedure. The purified protein migrated on SDS/PAGE as a single band with an apparent M(r) of 22,100. This enzyme favoured the hydrolysis of several arylesters and was classified as an arylesterase (EC 3.1.1.2). N-Terminal analysis showed that Ser-20 was the first amino acid of the mature secreted protein, suggesting that the N-terminal 19 hydrophobic amino acids served as a signal peptide.

Translational control of anionic trypsinogen and amylase synthesis in rat pancreas in response to caerulein stimulation

Infusion of rats with optimal doses of caerulein for up to 24 hr resulted in divergent changes in protein synthesis in the exocrine pancreas: a 3-fold increase in synthesis of anionic trypsinogen and a 75% decrease in synthesis of amylase. Lipase synthesis showed no change. Rates of total protein synthesis increased 2-fold, while DNA, RNA, and poly(A)+ mRNA concentrations were unchanged during hormonal stimulation. mRNA concentrations for anionic trypsinogen, lipase, and amylase were determined by dot blot hybridization analysis with cDNA and cRNA probes. Despite 12-fold changes in the ratio of synthesis of anionic trypsinogen to amylase at 24 hr of caerulein stimulation, changes in levels of mRNA encoding these two proteins were not observed. The slight decreases observed in amylase mRNA concentrations were found in both hormone and saline-infused animals. In vitro pulse-chase experiments after 12 hr of saline or caerulein infusion indicated that differential turnover of anionic trypsinogen and amylase did not occur during hormone stimulation. These data demonstrate that the differential regulation observed in protein synthesis that results from a single period of hormone stimulation is mediated by differential regulation of mRNA translation. The high degree of conservation observed in the 5' terminal sequences of both amylase and anionic trypsinogen mRNAs between mouse, rat, and dog suggests that sequence-specific mechanisms and secondary structure may play a role in the translational control of these two mRNAs.