Hereditary pancreatitis-associated mutation asn(21) --> ile stabilizes rat trypsinogen in vitro

Mouse model of PRSS1 p.R122H-related hereditary pancreatitis highlights context-dependent effect of autolysis-site mutation

Mutation p.R122H in human cationic trypsinogen (PRSS1) is the most frequently identified cause of hereditary pancreatitis. The mutation blocks protective degradation of trypsinogen by chymotrypsin C (CTRC), which involves an obligatory trypsin-mediated cleavage at Arg122. Previously, we found that C57BL/6N mice are naturally deficient in CTRC, and trypsinogen degradation is catalyzed by chymotrypsin B1 (CTRB1). Here, we used biochemical experiments to demonstrate that the cognate p.R123H mutation in mouse cationic trypsinogen (isoform T7) only partially prevented CTRB1-mediated degradation. We generated a novel C57BL/6N mouse strain harboring the p.R123H mutation in the native T7 trypsinogen locus. T7R123H mice developed no spontaneous pancreatitis, and severity parameters of cerulein-induced pancreatitis trended only slightly higher than those of C57BL/6N mice. However, when treated with cerulein for 2 days, more edema and higher trypsin activity was seen in the pancreas of T7R123H mice compared to C57BL/6N controls. Furthermore, about 40% of T7R123H mice progressed to atrophic pancreatitis in 3 days, whereas C57BL/6N animals showed full histological recovery. Taken together, the observations indicate that mutation p.R123H inefficiently blocks chymotrypsin-mediated degradation of mouse cationic trypsinogen, and modestly increases cerulein-induced intrapancreatic trypsin activity and pancreatitis severity. The findings support the notion that the pathogenic effect of the PRSS1 p.R122H mutation in hereditary pancreatitis is dependent on its ability to defuse chymotrypsin-dependent defenses.

Tighter Control by Chymotrypsin C (CTRC) Explains Lack of Association between Human Anionic Trypsinogen and Hereditary Pancreatitis

The human pancreas expresses two major trypsinogen isoforms, cationic trypsinogen (PRSS1) and anionic trypsinogen (PRSS2). Mutations in PRSS1 cause hereditary pancreatitis by altering cleavage of regulatory nick sites by chymotrypsin C (CTRC) resulting in reduced trypsinogen degradation and increased autoactivation. Despite 90% identity with PRSS1 and a strong propensity for autoactivation, mutations in PRSS2 are not found in hereditary pancreatitis suggesting that activation of this isoform is more tightly regulated. Here, we demonstrated that CTRC promoted degradation and thereby markedly suppressed autoactivation of human anionic trypsinogen more effectively than previously observed with cationic trypsinogen. Increased sensitivity of anionic trypsinogen to CTRC-mediated degradation was due to an additional cleavage site at Leu-148 in the autolysis loop and the lack of the conserved Cys-139-Cys-206 disulfide bond. Significant stabilization of anionic trypsinogen against degradation was achieved by simultaneous mutations of CTRC cleavage sites Leu-81 and Leu-148, autolytic cleavage site Arg-122, and restoration of the missing disulfide bridge. This stands in stark contrast to cationic trypsinogen where single mutations of either Leu-81 or Arg-122 resulted in almost complete resistance to CTRC-mediated degradation. Finally, processing of the trypsinogen activation peptide at Phe-18 by CTRC inhibited autoactivation of anionic trypsinogen, although cationic trypsinogen was strongly stimulated. Taken together, the observations indicate that human anionic trypsinogen is controlled by CTRC in a manner that individual natural mutations are unlikely to increase stability enough to promote intra-pancreatic activation. This unique biochemical property of anionic trypsinogen explains the lack of association of PRSS2 mutations with hereditary pancreatitis.

Autoactivation of mouse trypsinogens is regulated by chymotrypsin C via cleavage of the autolysis loop

Chymotrypsin C (CTRC) is a proteolytic regulator of trypsinogen autoactivation in humans. CTRC cleavage of the trypsinogen activation peptide stimulates autoactivation, whereas cleavage of the calcium binding loop promotes trypsinogen degradation. Trypsinogen mutations that alter these regulatory cleavages lead to increased intrapancreatic trypsinogen activation and cause hereditary pancreatitis. The aim of this study was to characterize the regulation of autoactivation of mouse trypsinogens by mouse Ctrc. We found that the mouse pancreas expresses four trypsinogen isoforms to high levels, T7, T8, T9, and T20. Only the T7 activation peptide was cleaved by mouse Ctrc, causing negligible stimulation of autoactivation. Surprisingly, mouse Ctrc poorly cleaved the calcium binding loop in all mouse trypsinogens. In contrast, mouse Ctrc readily cleaved the Phe-150-Gly-151 peptide bond in the autolysis loop of T8 and T9 and inhibited autoactivation. Mouse chymotrypsin B also cleaved the same peptide bond but was 7-fold slower. T7 was less sensitive to chymotryptic regulation, which involved slow cleavage of the Leu-149-Ser-150 peptide bond in the autolysis loop. Modeling indicated steric proximity of the autolysis loop and the activation peptide in trypsinogen, suggesting the cleaved autolysis loop may directly interfere with activation. We conclude that autoactivation of mouse trypsinogens is under the control of mouse Ctrc with some notable differences from the human situation. Thus, cleavage of the trypsinogen activation peptide or the calcium binding loop by Ctrc is unimportant. Instead, inhibition of autoactivation via cleavage of the autolysis loop is the dominant mechanism that can mitigate intrapancreatic trypsinogen activation.

Hereditary pancreatitis for the endoscopist

Hereditary pancreatitis shares a majority of clinical and morphologic features with chronic alcoholic pancreatitis, but may present at an earlier age. The term hereditary pancreatitis has primarily been associated with mutations in the serine protease 1 gene (PRSS1) which encodes for cationic trypsinogen. PRSS1 mutations account for approximately 68-81% of hereditary pancreatitis. Mutations in other genes, primarily serine protease inhibitor Kazal type 1 (SPINK1) and the cystic fibrosis transmembrane conductance regulator (CFTR) are also associated with hereditary pancreatitis. While chronic alcoholic pancreatitis may develop in the fourth or fifth decades, patients with hereditary pancreatitis may develop symptoms in the first or second decades of life. Hereditary pancreatitis is diagnosed either by detecting a causative gene mutation or by the presence of chronic pancreatitis in two first-degree or three second-degree relatives, in two or more generations, without precipitating factors and with a negative workup for known causes. Patients with hereditary pancreatitis may have recurrent acute pancreatitis and may develop pancreatic exocrine and endocrine insufficiency. Hereditary pancreatitis may involve premature trypsinogen activation or decreased control of trypsin. Recurrent inflammation can lead to acute pancreatitis and subsequently to chronic pancreatitis with parenchymal calcification. There is a markedly increased risk of pancreatic carcinoma compared with the general population. Patients are often referred for evaluation of pancreatitis, biliary or pancreatic ductal dilatation, jaundice, biliary obstruction, pancreatic duct stone or stricture, pancreatic pseudocysts, and for evaluation for malignancy. Medical treatment includes pancreatic enzyme supplementation, nutritional supplementation, diabetes management, and palliation of pain. Patients should avoid tobacco use and alcohol exposure. Hereditary pancreatitis is reviewed and recommendations for genetic testing are discussed.

Characterisation of a transgenic mouse expressing R122H human cationic trypsinogen

BACKGROUND

The R122H mutation of the cationic trypsinogen was found in patients with hereditary pancreatitis. A transgenic animal carrying this mutation could be useful as a genetic model system of pancreatitis.

METHODS

Mice transgenic for the human R122H cationic trypsinogen were generated using the -205 fragment of the rat elastase promoter. The presence of the transgene was assayed in the DNA, in pancreatic mRNA and in zymogen granule lysates. Serum levels of amylase, lipase and cytokines (MCP-1, IL-6) were monitored and the histological appearance of the tissue was investigated. Pancreatitis was induced by 7 hourly injections of 50 mug/kg cerulein. The procedure was repeated twice weekly for 10 consecutive weeks. The animals were sacrificed 24 (n = 8) and 48 hours (n = 8) after the first injection and at the end of the whole treatment (n = 7).

RESULTS

The transgene was detected at the genomic level and in pancreatic mRNA. The corresponding protein was found in low amounts in zymogen granule lysates. R122H mice showed elevated pancreatic lipase, but there was no spontaneous development of pancreatitis within 18 months. After induction of pancreatitis, levels of lipase (after 24 hours) and amylase (after 48 hours) were higher in R122H mice compared to controls. Repeated treatment with cerulein resulted in a slightly more severe pancreatitis in R122H animals. Amylase, lipase, and the cytokine levels were similar to controls.

CONCLUSION

The R122H transgenic mouse failed to develop a spontaneous pancreatitis but a repeatedly provoked cerulein-induced pancreatitis led to a slightly more severe pancreatitis. The rather small difference in comparison to controls could be due to the low expression of the transgene in the mouse pancreas.

Mutations of human cationic trypsinogen (PRSS1) and chronic pancreatitis

Ten years ago, the groundwork for the discovery of the genetic basis of chronic pancreatitis was laid by linkage analyses of large kindreds with autosomal dominant hereditary chronic pancreatitis. Subsequent candidate gene sequencing of the 7q35 chromosome region revealed a strong association of the c.365G > A (p.R122 H) mutation of the PRSS1 gene encoding cationic trypsinogen with hereditary pancreatitis. In the following years, further mutations of this gene were discovered in patients with hereditary or idiopathic chronic pancreatitis. In vitro the mutations increase autocatalytic conversion of trypsinogen to active trypsin and thus probably cause premature, intrapancreatic trypsinogen activation in vivo. The clinical presentation is highly variable, but most affected mutation carriers have relatively mild disease. In this review, we summarize the current knowledge on trypsinogen mutations and their role in pancreatic diseases.

Biochemical models of hereditary pancreatitis

The past decade has witnessed remarkable progress in the genetics of chronic pancreatitis. Despite these accomplishments, the understanding of the molecular mechanisms through which PRSS1 and SPINK1 mutations cause chronic pancreatitis has remained sketchy. Pancreatitis-associated gene mutations are believed to result in uncontrolled trypsin activity in the pancreas. Experimental identification of the disease-relevant functional alterations caused by PRSS1 or SPINK1 mutations proved to be challenging, however, because results of biochemical analyses lent themselves to different interpretations. This article focuses on PRSS1 mutations and summarizes the salient biochemical findings in the context of the mechanistic models that explain the connection between mutations and hereditary pancreatitis.

Germline mutations and gene polymorphism associated with human pancreatitis

A wide range of mutations and polymorphisms in genes that relate to pancreatic function seem to be involved in the development of pancreatitis. Some of these genetic alterations lead to disease phenotypes with unequivocal mendelian inheritance patterns, whereas others seem to act as modifier genes in conjunction with environ-mental or, as yet unidentified, genetic cofactors. This article reviews germline changes in the genes for trypsin, pancreatic secretory trypsin inhibitor, the cystic fibrosis conductance regulator, lipid metabolism proteins, inflammatory mediators for cytokines, and cathepsin B.

The genetic and molecular bases of monogenic disorders affecting proteolytic systems

Complete and limited proteolysis represents key events that regulate many biological processes. At least 5% of the human genome codes for components of proteolytic processes if proteases, inhibitors, and cofactors are taken into account. Accordingly, disruption of proteolysis is involved in numerous pathological conditions. In particular, molecular genetic studies have identified a growing number of monogenic disorders caused by mutations in protease coding genes, highlighting the importance of this class of enzymes in development, organogenesis, immunity, and brain function. This review provides insights into the current knowledge about the molecular genetic causes of these disorders. It should be noted that most are due to loss of function mutations, indicating absolute requirement of proteolytic activities for normal cellular functions. Recent progress in understanding the function of the implicated proteins and the disease pathogenesis is detailed. In addition to providing important clues to the diagnosis, treatment, and pathophysiology of disease, functional characterisation of mutations in proteolytic systems emphasises the pleiotropic functions of proteases in the body homeostasis.

Expression of mutated cationic trypsinogen reduces cellular viability in AR4-2J cells

Mutations in the human cationic trypsinogen are associated with hereditary pancreatitis. The cDNA coding for human cationic trypsinogen was subcloned into the expression vector pcDNA3. The mutations R122H, N29I, A16V, D22G, and K23R were introduced by site directed mutagenesis. We constructed an expression vector coding for active trypsin by subcloning the cDNA of trypsin lacking the coding region for the trypsin activating peptide behind an appropriate signal peptide. Expression of protein was verified by Western blot and measurement of enzymatic activity. AR4-2J cells were transiently transfected with the different expression vectors and cell viability and intracellular caspase-3 activity were quantified. In contrast to wild-type trypsinogen, expression of active trypsin and mutated trypsinogens reduced cell viability of AR4-2J cells. Expression of trypsin and R122H trypsinogen induced caspase-3 activity. Acinar cells might react to intracellular trypsin activity by triggering apoptosis.

Hereditary pancreatitis: clinical characteristics and diagnostic criteria in Japan

BACKGROUND/AIM

Hereditary pancreatitis (HP) is the strongest known risk factor for pancreatic cancer. The aim of the present study is to establish diagnostic criteria for HP to predict and identify high-risk groups for pancreatic cancer.

METHOD

We collected clinical data for 210 patients with recurrent acute or chronic pancreatitis, and examined mutations of the cationic trypsinogen (CT) gene in 57 patients with a family history of pancreatitis or with early-onset idiopathic recurrent acute or chronic pancreatitis (40 years of age or younger). DNA was extracted from peripheral blood leukocytes, and exons 2 and 3 of the CT gene were individually amplified by polymerase chain reaction (PCR) and sequenced.

RESULTS

Of these 57 patients in whom mutations of the CT gene were examined, the R122H (20 patients) and N29I (5 patients) mutations in the CT gene were observed in 25 patients (43.9%). From the analysis of clinical records and the CT gene of these patients, we proposed the following adaptations to the diagnostic criteria for HP: (1) at least one of the affected members in a family has no known etiological factors, (2) we deleted the definition of "different generation", but included the upper limit of the age of onset of pancreatitis in the case of siblings (at least 1 of the patients in a family <40 years of age). According to these criteria, all patients with the CT gene mutations in the present study could be classified as having HP, with the exception of 2 sporadic cases with the R122H and N29I mutations, respectively. Based on these findings, we revised the criteria for the diagnosis of HP; (1) recurrent acute or chronic pancreatitis with R122H or N29I mutation of the CT gene, or (2) recurrent acute or chronic pancreatitis with a family history of 2 or more affected patients, irrespective of generation, with at least 1 of the patients having no known etiological factors, and in case of siblings only, the onset of the disease in at least 1 of the patients is under age 40 years.

CONCLUSION

The revised criteria in the present study are appropriate and of clinical usefulness to diagnose patients with HP even in cases without the genetic testing. However, if and when more genes are detected, it will be important to reexamine the mutation-negative patients now classified as HP based on our proposed criteria.

Human mesotrypsin is a unique digestive protease specialized for the degradation of trypsin inhibitors

Mesotrypsin is an enigmatic minor human trypsin isoform, which has been recognized for its peculiar resistance to natural trypsin inhibitors such as soybean trypsin inhibitor (SBTI) or human pancreatic secretory trypsin inhibitor (SPINK1). In search of a biological function, two conflicting theories proposed that due to its inhibitor-resistant activity mesotrypsin could prematurely activate or degrade pancreatic zymogens and thus play a pathogenic or protective role in human pancreatitis. In the present study we ruled out both theories by demonstrating that mesotrypsin was grossly defective not only in inhibitor binding, but also in the activation or degradation of pancreatic zymogens. We found that the restricted ability of mesotrypsin to bind inhibitors or to hydrolyze protein substrates was solely due to a single evolutionary mutation, which changed the serine-protease signature glycine 198 residue to arginine. Remarkably, the same mutation endowed mesotrypsin with a novel and unique function: mesotrypsin rapidly hydrolyzed the reactive-site peptide bond of the Kunitz-type trypsin inhibitor SBTI, and irreversibly degraded the Kazal-type temporary inhibitor SPINK1. The observations suggest that the biological function of human mesotrypsin is digestive degradation of trypsin inhibitors. This mechanism can facilitate the digestion of foods rich in natural trypsin inhibitors. Furthermore, the findings raise the possibility that inappropriate activation of mesotrypsinogen in the pancreas might lower protective SPINK1 levels and contribute to the development of human pancreatitis. In this regard, it is noteworthy that the well known pathological trypsinogen activator cathepsin B exhibited a preference for the activation of mesotrypsinogen of all three human trypsinogen isoforms, suggesting a biochemical mechanism for mesotrypsinogen activation in pancreatic acinar cells.

Genetic basis of chronic pancreatitis

BACKGROUND

Pancreatitis has a proven genetic basis in a minority of patients.

METHODS

Review of the literature on genetics of pancreatitis.

RESULTS

Ever since the discovery that in most patients with hereditary pancreatitis a mutation in the gene encoding for cationic trypsinogen (R122H) was found that results in a gain of trypsin function', many other mutations in the cationic trypsinogen gene, as well as in the gene encoding for pancreatic secretory trypsin inhibitor, have been found in patients with chronic pancreatitis. Furthermore, mutations in other genes, like the mucoviscoidosis-gene encoding for a chloride channel, and in genes encoding for enzymes involved in the metabolism of ethanol, have been linked to chronic pancreatitis. This article reviews the highlights that have been achieved in this field of pancreatic research.

CONCLUSIONS

Recent data suggest that genetics may play a role in the pathogenesis of pancreatitis.

The pathobiochemistry of hereditary pancreatitis: studies on recombinant human cationic trypsinogen

BACKGROUND/AIMS

This study attempts to identify the biochemical alterations in human cationic trypsinogen and trypsin caused by the hereditary pancreatitis-associated mutations Arg117-->His and Asn21-->Ile.

METHODS

Recombinant wild-type and mutant human cationic trypsinogens were expressed in Escherichia coli and purified to homogeneity, and trypsin autolysis and trypsinogen autoactivation were characterized.

RESULTS

Both mutations significantly enhanced the autoactivation of human cationic trypsinogen. In addition, the Arg117-->His mutation inhibited autocatalytic inactivation of trypsin, while the Asn21-->Ile mutation had no such effect.

CONCLUSIONS

The findings support the notion that enhanced trypsinogen activation in the pancreas is the common initiating step in hereditary pancreatitis, whereas trypsin stabilization plays a role in cases associated with the Arg117-->His mutation.

Hereditary pancreatitis: a model for inflammatory diseases of the pancreas

Acute and chronic pancreatitis remain among the most recalcitrant of all diseases to investigation and intervention. In the majority of patients, excessive alcohol consumption is associated with development of the disease. Therefore, several theories have been proposed seeking to explain the relationship between alcohol and the development of acute and chronic pancreatitis. However, recent investigations in hereditary pancreatitis provided important insights into chronic pancreatitis pathogenesis and offer an important model for understanding pancreatic inflammation. This article highlights several advances gained from investigating hereditary pancreatitis kindreds, and reviews the TIGAR-O risk/aetiology classification system. Finally, the major independent theories on development of chronic pancreatitis are reviewed with respect to the SAPE hypothesis of chronic pancreatitis pathogenesis.

Human cationic trypsinogen. Arg(117) is the reactive site of an inhibitory surface loop that controls spontaneous zymogen activation

Mutation of Arg(117), an autocatalytic cleavage site, is the most frequent amino acid change found in the cationic trypsinogen (Tg) of patients with hereditary pancreatitis. In the present study, the role of Arg(117) was investigated in wild-type cationic Tg and in the activation-resistant Lys(15) --> Gln mutant (K15Q-Tg), in which Tg-specific properties of Arg(117) can be examined selectively. We found that trypsinolytic cleavage of the Arg(117)-Val(118) bond did not proceed to completion, but due to trypsin-catalyzed re-synthesis an equilibrium was established between intact Tg and its cleaved, two-chain form. In the absence of Ca(2+), at pH 8.0, the hydrolysis equilibrium (K(hyd) = [cleaved Tg]/[intact Tg]) was 5.4, whereas 5 mm Ca(2+) reduced the rate of cleavage at Arg(117) at least 20-fold, and shifted K(hyd) to 0.7. These observations indicate that the Arg(117)-Val(118) bond exhibits properties analogous to the reactive site bond of canonical trypsin inhibitors and suggest that this surface loop might serve as a low affinity inhibitor of zymogen activation. Consistent with this notion, autoactivation of cationic Tg was inhibited by the cleaved form of K15Q-Tg, with an estimated K(i) of 80 microm, while no inhibition was observed with K15Q-Tg carrying the Arg(117) --> His mutation. Finally, zymogen breakdown due to other trypsinolytic pathways was shown to proceed almost 2000-fold slower than cleavage at Arg(117). Taken together, the findings suggest two independent, successively functional trypsin-mediated mechanisms against pathological Tg activation in the pancreas. At low trypsin concentrations, cleavage at Arg(117) results in inhibition of trypsin, whereas high trypsin concentrations degrade Tg, thus limiting further zymogen activation. Loss of Arg(117)-dependent trypsin inhibition can contribute to the development of hereditary pancreatitis associated with the Arg(117) --> His mutation.

Hereditary pancreatitis caused by a novel PRSS1 mutation (Arg-122 --> Cys) that alters autoactivation and autodegradation of cationic trypsinogen

Hereditary pancreatitis has been found to be associated with germline mutations in the cationic trypsinogen (PRSS1) gene. Here we report a family with hereditary pancreatitis that carries a novel PRSS1 mutation (R122C). This mutation cannot be diagnosed with the conventional screening method using AflIII restriction enzyme digest. We therefore propose a new assay based on restriction enzyme digest with BstUI, a technique that permits detection of the novel R122C mutation in addition to the most common R122H mutation, and even in the presence of a recently reported neutral polymorphism that prevents its detection by the AflIII method. Recombinantly expressed R122C mutant human trypsinogen was found to undergo greatly reduced autoactivation and cathepsin B-induced activation, which is most likely caused by misfolding or disulfide mismatches of the mutant zymogen. The K(m) of R122C trypsin was found to be unchanged, but its k(cat) was reduced to 37% of the wild type. After correction for enterokinase activatable activity, and specifically in the absence of calcium, the R122C mutant was more resistant to autolysis than the wild type and autoactivated more rapidly at pH 8. Molecular modeling of the R122C mutant trypsin predicted an unimpaired active site but an altered stability of the calcium binding loop. This previously unknown trypsinogen mutation is associated with hereditary pancreatitis, requires a novel diagnostic screening method, and, for the first time, raises the question whether a gain or a loss of trypsin function participates in the onset of pancreatitis.

Comparative in vitro studies on native and recombinant human cationic trypsins. Cathepsin B is a possible pathological activator of trypsinogen in pancreatitis

Hereditary pancreatitis, an autosomal dominant disease is believed to be caused by mutation in the human trypsinogen gene. The role of mutations has been investigated by in vitro studies using recombinant rat and human trypsinogen (TG). In this study we compare the enzymatic properties and inhibition by human pancreatic secretory trypsin inhibitor (hPSTI) of the native, postsynthetically modified and recombinant cationic trypsin, and found these values practically identical. We also determined the autolytic stability of recombinant wild type (Hu1Asn21) and pancreatitis-associated (Hu1Ile21) trypsin. Both forms were equally stable. Similarly, we found no difference in the rate of activation of the two zymogens by human cationic and anionic trypsin. Mesotrypsin did not activate either form. The rate of autocatalytic activation of Hu1Asn21 TG and Hu1Ile21 TG was also identical at pH 8 both in the presence and absence of Ca2+. At pH 5 Hu1Ile21 TG autoactivated about twice as fast as Hu1Asn21 TG. The presence of physiological amount of hPSTI completely prevented autoactivation of both zymogens at pH 8 and at pH 5 as well. Cathepsin B readily activated both zymogens although Hu1Ile21 TG was activated about 2.5-3 times as fast as Hu1Asn21 TG. The presence of hPSTI did not prevent the activation of zymogens by cathepsin B. Our results underlie the central role of cathepsin B in the development of different forms of pancreatitis.

Chronic pancreatitis: diagnosis, classification, and new genetic developments

The utilization of recent advances in molecular and genomic technologies and progress in pancreatic imaging techniques provided remarkable insight into genetic, environmental, immunologic, and pathobiological factors leading to chronic pancreatitis. Translation of these advances into clinical practice demands a reassessment of current approaches to diagnosis, classification, and staging. We conclude that an adequate pancreatic biopsy must be the gold standard against which all diagnostic approaches are judged. Although computed tomography remains the initial test of choice for the diagnosis of chronic pancreatitis, the roles of endoscopic retrograde pancreatography, endoscopic ultrasonography, and magnetic resonance imaging are considered. Once chronic pancreatitis is diagnosed, proper classification becomes important. Major predisposing risk factors to chronic pancreatitis may be categorized as either (1) toxic-metabolic, (2) idiopathic, (3) genetic, (4) autoimmune, (5) recurrent and severe acute pancreatitis, or (6) obstructive (TIGAR-O system). After classification, staging of pancreatic function, injury, and fibrosis becomes the next major concern. Further research is needed to determine the clinical and natural history of chronic pancreatitis developing in the context of various risk factors. New methods are needed for early diagnosis of chronic pancreatitis, and new therapies are needed to determine whether interventions will delay or prevent the progression of the irreversible damage characterizing end-stage chronic pancreatitis.

Gain-of-function mutations associated with hereditary pancreatitis enhance autoactivation of human cationic trypsinogen

Hereditary pancreatitis (HP), an autosomal dominant disorder, has been associated with mutations in the cationic trypsinogen gene. Here we demonstrate that the two most frequent HP mutations, Arg117 --> His and Asn21 --> Ile, significantly enhance autoactivation of human cationic trypsinogen in vitro, in a manner that correlates with the severity of clinical symptoms in HP. In addition, mutation Arg117 --> His inhibits autocatalytic inactivation of trypsin, while mutation Asn21 --> Ile has no such effect. The findings strongly argue that increased trypsinogen activation in the pancreas is the common initiating step in both forms of HP, whereas trypsin stabilization might also contribute to HP associated with the Arg117 --> His mutation.

Chronic pancreatitis

In the past year, there has been at least one important clinical paper that sheds light on the character and natural history of painful chronic pancreatitis, which has important clinical implications. In addition, several novel mutations have been described in the cationic trypsinogen gene in patients with hereditary pancreatitis. The mechanism by which these mutations cause pancreatic disease remains speculative. The diagnosis of early chronic pancreatitis is controversial. A novel noninvasive pancreatic function test (measurement of postprandial APOB-48) was reported but is unlikely to be a sensitive test of pancreatic function. Pancreatic fibrosis is frequently seen in alcoholics without chronic pancreatitis, and this makes it difficult to interpret the findings on endoscopic ultrasonogram. Recent studies highlight the difficulty in abolishing pancreatic steatorrhea. Recently fibrosing colonopathy in adult patients has been reported. Extracorporeal shockwave lithotripsy combined with endoscopic therapy failed to benefit patients with calcific chronic pancreatitis.

SPINK1/PSTI polymorphisms act as disease modifiers in familial and idiopathic chronic pancreatitis

BACKGROUND & AIMS

Gain-of-function trypsin mutations cause acute pancreatitis and chronic pancreatitis. Loss of trypsin inhibitor function may have similar effects. We investigated the prevalence of SPINK1 (PSTI) mutations in familial pancreatitis, idiopathic chronic pancreatitis, and controls.

METHODS

Genetic-linkage studies were performed in 5 familial pancreatitis families. The entire SPINK1 gene was sequenced in 112 affected individuals and 95 control DNA samples, and exon 3 was sequenced in 95 additional controls. X-ray crystallography-based model building and statistical studies were performed.

RESULTS

Significant linkage between pancreatitis and 5q31.1-2 was excluded. Novel SPINK1 mutations, one D50E mutation, one IVS3+125 C>A, and five IVS3+184 T>A intronic polymorphisms were identified. The N34S and P55S mutations were observed in 29 of 112 patients (25%) as N34S/N34S (n = 7), N34S/wt (n = 19), N34S/P55S (n = 2), and N34S/D50E (n = 1). Three hundred eighty control alleles revealed 3 N34S (0.77%), 2 P55S (0.53%), and no D50E mutations. Age of disease onset and severity were similar between homozygous and heterozygous patients. Structural modeling revealed several possible pathophysiologic mechanisms for the N34S mutation.

CONCLUSIONS

SPINK1 mutations are common in the population (approximately 2%), but are clearly associated with pancreatitis. The mutation-associated risk is low. Modeling and familial clustering suggest that SPINK1 mutations are disease modifying, possibly by lowering the threshold for pancreatitis from other genetic or environmental factors, but by themselves do not cause disease.

High-affinity Ca(2+) binding inhibits autoactivation of rat trypsinogen

The recent discovery that mutation Asn21 --> Ile in the human cationic trypsinogen (Tg) is associated with hereditary pancreatitis has brought into focus the functional role of amino acid 21 in mammalian Tgs. In the present paper, the effect of mutations Thr21 --> Asn and Thr21 --> Ile on the Ca(2+) dependence of zymogen activation was investigated, using the autolysis-resistant rat Tg mutant Arg117 --> His. In the absence of Ca(2+), rat Tg exhibited low but significant basal autoactivation, which was inhibited by micromolar concentrations of Ca(2+) (IC(50) 2.6 microM). Interestingly, basal autoactivation was diminished in both mutants, and no further inhibition by micromolar Ca(2+) was detectable. Millimolar Ca(2+) concentrations markedly and comparably stimulated autoactivation of wild-type and mutant zymogens (EC(50) 1.7-2.4 mM). The results indicate that rat Tg is subject to dual regulation by Ca(2+), allowing zymogen stabilization in a low-Ca(2+) environment and efficient activation in a high-Ca(2+) milieu.

Chronic pancreatitis associated with an activation peptide mutation that facilitates trypsin activation

BACKGROUND & AIMS

Mutations of the cationic trypsinogen have been described in hereditary pancreatitis. We report a new trypsinogen mutation in the activation peptide of the proenzyme in a family with chronic pancreatitis.

METHODS

The coding region of the cationic trypsinogen gene was sequenced after polymerase chain reaction amplification. The following peptides homologous to the N-terminal end of cationic trypsinogen were synthesized (one-letter code, mutated amino acid underlined): wild-type peptide, APFDDDDKIVGG; pD22G, APFDDDGKIVGG; pK23R, APFDDDDRIVGG. The sequences of pD22G and pK23R correspond to the recently identified mutation K23R and to the mutation described here (D22G). To mimic trypsinogen activation, these peptides were digested with trypsin for 30 minutes at pH 5.0-8. 0, and the fragments were analyzed by high-performance liquid chromatography.

RESULTS

In a family with clinical evidence of hereditary chronic pancreatitis, a missense mutation of codon 22 (GAC-->GGC) of the cationic trypsinogen was found. This mutation results in a substitution of aspartic acid by glycine; therefore, the mutation was called D22G. Chromatographic analysis of tryptic digests of the peptides pD22G and pK23R showed hydrolysis rates of 22% and 75%, respectively, whereas the wild-type peptide was hydrolyzed at only 6%. The cleavage rates were reduced at lower pH, and no hydrolysis occurred without trypsin.

CONCLUSIONS

The activation peptides of the trypsinogen variants D22G and K23R could be released at a higher rate than in wild-type trypsinogen, resulting in increased amounts of trypsin in the pancreas, which could initiate pancreatitis.

Human cationic trypsinogen. Role of Asn-21 in zymogen activation and implications in hereditary pancreatitis

Mutation Asn-21 --> Ile in human cationic trypsinogen (Tg-1) has been associated with hereditary pancreatitis. Recent studies with rat anionic Tg (Tg-2) indicated that the analogous Thr-21 --> Ile mutation stabilizes the zymogen against autoactivation, whereas it has no effect on catalytic properties or autolytic stability of trypsin (Sahin-Tóth, M. (1999) J. Biol. Chem. 274, 29699-29704). In the present paper, human cationic Tg (Asn-21-Tg) and mutants Asn-21 --> Ile (Ile-21-Tg) and Asn-21 --> Thr (Thr-21-Tg) were expressed in Escherichia coli, and zymogen activation, zymogen degradation, and trypsin autolysis were studied. Enterokinase activated Asn-21-Tg approximately 2-fold better than Ile-21-Tg or Thr-21-Tg, and catalytic parameters of trypsins were comparable. At 37 degrees C, in 5 mm Ca(2+), all three trypsins were highly stable. In the absence of Ca(2+), Asn-21- and Ile-21-trypsins suffered autolysis in an indistinguishable manner, whereas Thr-21-trypsin exhibited significantly increased stability. In sharp contrast to observations with the rat proenzyme, at pH 8.0, 37 degrees C, autoactivation kinetics of Asn-21-Tg and Ile-21-Tg were identical; however, at pH 5. 0, Ile-21-Tg autoactivated at an enhanced rate relative to Asn-21-Tg. Remarkably, at both pH values, Thr-21-Tg showed markedly higher autoactivation rates than the two other zymogens. Finally, autocatalytic proteolysis of human zymogens was limited to cleavage at Arg-117, and no digestion at Lys-188 was detected. The observations indicate that zymogen stabilization by Ile-21 as observed in rat Tg-2 is not characteristic of human Tg-1. Instead, an increased propensity to autoactivation under acidic conditions might be relevant to the pathomechanism of the Asn-21 --> Ile mutation in hereditary pancreatitis. In the same context, faster autoactivation and increased trypsin stability caused by the Asn-21 --> Thr mutation in human Tg-1 might provide a rationale for the evolutionary divergence from Thr-21 found in other mammalian trypsinogens.

Genes, cloned cDNAs, and proteins of human trypsinogens and pancreatitis-associated cationic trypsinogen mutations

Historically, trypsinogens/trypsins have been one of the most extensively studied enzyme models of protein structure and function. They have received renewed attention after the identification of mutations in the cationic trypsinogen gene as being associated with hereditary pancreatitis. A survey of the literature revealed five cloned cDNAs, but only three protein products of human trypsinogens, and their nomenclature has been confusing. The availability of the complete genomic sequencing of the human trypsinogen gene family made it possible to provide a systematic review of the genes, cDNAs, and protein products of human trypsinogens and to clarify some controversial issues. Further, the confusing coexistence of two systems for naming the cationic trypsinogen mutations is addressed.