Roles of molecular chaperones in pancreatic secretion and their involvement in intestinal absorption

This review focuses on the contribution of molecular chaperones in the secretory process of digestive enzymes and their interaction with enterocytes. By using biochemistry and immunocytochemistry, we have shown that Grp94, Cpn10, Cpn60, and protein disulfide isomerase (PDI) are present all along the rough endoplasmic reticulum-Golgi-granule secretory pathway of the pancreatic acinar cells and are secreted into the acinar lumen. Two other molecular chaperones, Grp78 and the Hsp70, appear to be restricted to the rough endoplasmic reticulum and the trans-Golgi apparatus, respectively. We have found that chaperones can be associated with pancreatic enzymes along the secretory pathway. Indeed, double immunogold and immunocoprecipitation revealed an association between Cpn60 and the colipase-dependent lipase (CDL) and between Grp94 and the bile salt-dependent lipase (BSDL). These complexes are secreted into the acinar lumen and diverted to the duodenal lumen. These findings led us to investigate these enzyme-chaperone complexes in intestinal tissue. Grp94, Cpn60, and PDI are present on microvilli and on the endosomal compartment of enterocytes. Furthermore, we have shown that the Grp94-BSDL complexes are internalized by enterocytes through classical endocytosis. Upon dissociation of the BSDL-Grp94 complex in the late endosome, BSDL is transferred to the basolateral membrane. We propose that Grp94 interacts with specific receptors and/or could force the associated protein to adopt a specific conformation that allows its binding to corresponding membrane receptors and its internalization by enterocytes. These two hypotheses need not to be exclusive. The existence of such a pancreatic secretion-intestinal absorption link speaks in favor of a coordinated functional connection between these two entities, through molecular chaperones, in order to optimize intestinal activities.

Prevalence of antibodies to Leptospira serovars in sheep and goats in Alto Adige-South Tyrol

Serum samples from 313 sheep and 95 goats were collected during November 1993 in 26 localities in Alto Adige-South Tyrol and tested by microscopic agglutination test for antibodies to 28 serovars of the genus Leptospira. At the time of blood collection all the animals appeared healthy with no clinical sign suggestive of leptospirosis. The observed seroprevalence in sheep was 6.1%, whereas the seropositivity rate for goat serum samples was 2.1%. The highest serological prevalence in sheep was recorded for serovar castellonis, followed by poi, sejroe, hardjo subtype hardjobovis, copenhageni, and cynopteri. Titres to poi were the only ones found in goats. These findings, which are proof of Leptospira infection in Alto Adige-South Tyrol, indicate that foci of several serovars exist in this region.

Expression of a 70-kDa immunoreactive form of bile salt-dependent lipase by human pancreatic tumoral mia PaCa-2 cells

This work describes the characterization of an immunoreactive form of bile salt-dependent lipase (BSDL) expressed by the human pancreatic tumoral Mia PaCa-2 cell line. This BSDL-related protein, which has an M(r) of 70 kDa, is enzymatically active and poorly secreted. Furthermore, a protein with the same electrophoretic migration can also be immunoprecipitated with polyclonal antibodies specific for the human pancreatic BSDL after in vitro translation of RNA isolated from Mia PaCa-2 cells. These data indicated that this BSDL-related protein might be poorly, or not, glycosylated. Reverse transcription and amplification of RNA extracted from Mia PaCa-2 cells using primers able to specifically amplify the full-length mRNA of the human BSDL resulted in a detectable 1.8-kb cDNA product, shorter than that of BSDL (2.2 kb). The sequence of this transcript corresponds to the mRNA sequence that codes for the mature human pancreatic BSDL. However, a deletion of 330 bp is located within the 3'-domain of this cDNA. Therefore data allowed us to conclude that the 70-kDa BSDL-related protein is a 612 amino acid length protein and represents a truncated form of BSDL. The deletion of 110 amino acids occurs in the C-terminal region of the protein, which encompasses 6 tandemly repeated sequences instead of the 16 normally present in the sequence of BSDL. Because feto-acinar pancreatic protein (FAPP), which is the oncofetal counterpart of BSDL, is a C-terminally truncated isoform of BSDL, it is suggested that the 70-kDa BSDL-related protein expressed in MiaPaCa-2 cells could be representative of the protein moiety of FAPP.

Restoration of alpha(1,2) fucosyltransferase activity decreases adhesive and metastatic properties of human pancreatic cancer cells

The expression of alpha(1,2) fucosyltransferases that catalyze the fucose transfer to galactose of the N-acetyl(iso)lactosamine chain is decreased in human metastatic pancreatic cancer cells. alpha(2,3) Sialyltransferases catalyze the transfer of sialic acid to the same substrate to form, with alpha(1,3/1,4) fucosyltransferases, sialyl-Lewis a and sialyl-Lewis x determinants on cell surface that are involved in pancreatic metastatic invasion. The aim of this study was to determine whether this decrease of alpha(1,2) fucosyltransferase expression can favor the alpha(2,3) sialyltransferase activity to form metastatic sialyl-Lewis antigens. Restoration of alpha(1,2) fucosyltransferase activity in the human pancreatic cancer cell line BxPC-3 was obtained by selecting stable transfectants expressing FUT1. Overexpression of FUTI in BxPC-3 cells resulted in a substantial reduction of sialyl-Lewis antigen expression that correlated with an increase of expression of Lewis y and H-type antigens on cell surface. The modified oligosaccharide structures were preferentially restricted to three major glycoproteins, which could in part be related to mucin-type glycoproteins. The reduction of sialyl-Lewis antigen expression was associated with an inhibition of adhesive properties to E-selectin and a decrease of gastrointestinal metastatic power of BxPC-3 cells after xenograft transplantation into nude mice. This study provides evidence that the expression level of alpha(1,2) fucosyltransferase may regulate the expression of sialyl-Lewis a and sialyl-Lewis x antigens and consequently could play an important role in metastatic properties of human pancreatic cancer cells.

The affinity binding sites of pancreatic bile salt-dependent lipase in pancreatic and intestinal tissues

In previous studies, we have shown that the bile salt-dependent lipase (BSDL) associates with the Grp94 molecular chaperone, an association that appears to play essential roles in the folding of BSDL. More recently, combined biochemical and immunocytochemical investigations were carried out to show that the transport of BSDL occurs via an association with the Grp94 all along the pancreatic secretory route (ER-Golgi-granules). The Grp94-BSDL complex is secreted with the pancreatic juice into the acinar lumen and reaches the duodenal lumen, where it is internalized by enterocytes. The dissociation of the complex could take place within the endosomal compartment because BSDL continues further on its way to the basolateral membrane of the enterocyte. To localize the affinity binding sites of pancreatic BSDL in pancreatic and duodenal tissues, we have used an affinity-gold ultrastructural technique. BSDL coupled to gold particles appears to interact with specific sites in tissue sections. This was confirmed by another indirect morphological approach using biotin-labeled BSDL and streptavidin-gold complexes on tissue sections. We have shown that BSDL associates with sites in the pancreatic secretory pathway compartments and in the microvilli, the endosomal compartment, and the basolateral membrane of enterocytes. By biochemical approaches, biotin-labeled BSDL displayed affinities with proteins of 180-190 kD in both pancreatic and duodenal tissues. We have also shown that the Grp94-BSDL complexes, which are insensitive to denaturing conditions, are present in pancreatic homogenate but not in duodenal lysate. Thus, BSDL is able to bind protein complexes formed by either BSDL-Grp94 or Grp94 dimers. (J Histochem Cytochem 48:267-276, 2000)

Phosphorylation of the rat pancreatic bile-salt-dependent lipase by casein kinase II is essential for secretion

Bile-salt-dependent lipase (BSDL, EC 3.1.1.-) is an enzyme expressed by the pancreatic acinar cells and secreted as a component of the pancreatic juice of all examined species. During its secretion route BSDL is associated with intracellular membranes. This association allows the complete glycosylation of the enzyme or participates in the inhibition of the enzyme activity, which can deleterious for the acinar pancreatic cell. Thereafter, the human BSDL is phosphorylated by a serine/threonine protein kinase and released from intracellular membranes. In the present study, we show that the rat pancreatic BSDL, expressed by AR4-2J cells used as a model, is phosphorylated by a protein kinase that is insensitive to inhibitors of protein kinases A, C or G and that the phosphorylation process is favoured by okadaic acid (an inhibitor of protein phosphatases 1 and 2A). However, 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB), which is a specific inhibitor of casein kinase II, abolishes the phosphorylation in vitro of BSDL within micro- somes of AR4-2J pancreatic cells. We showed further that the alpha-subunit of casein kinase II co-locates with BSDL within the lumenal compartment of the Golgi. Genistein, which perturbs the trans-Golgi network, also inhibits the phosphorylation of BSDL, suggesting that this post-translational modification of BSDL probably occurred within this cell compartment. The inhibition of the phosphorylation of BSDL by DRB also decreases the rate at which the enzyme is secreted. Under the same conditions, the rate of alpha-amylase secretion was not modified. These data strongly suggest that phosphorylation is a post-translational event, which appears to be essential for the secretion of BSDL.

alpha(1,2)-fucosylation prevents sialyl Lewis x expression and E-selectin-mediated adhesion of fucosyltransferase VII-transfected cells

E-selectin is a cytokine-inducible, calcium-dependent endothelial cell adhesion molecule that plays a critical role in the leucocyte-endothelium interaction during inflammation and is thought to contribute to the metastatic dissemination of tumour cells. Like the other selectins, E-selectin binds to ligands carrying the tetrasaccharide sialyl-Lewis x (NeuAcalpha2,3Galbeta1,4[Fucalpha1, 3]GlcNAc)1 or its isomer sialyl-Lewis a (NeuAcalpha2, 3Galbeta1, 3[Fucalpha1,4]GlcNAc). We examined the effect of expressing the H-type alpha(1,2)-fucosyltransferase or the alpha(2, 6)-sialyltransferase on the synthesis of sialyl-Lewis x by alpha(1, 3)fucosyltransferase. We found that H-type alpha(1, 2)-fucosyltransferase but not alpha(2,6)-sialyltransferase, strongly inhibited sialyl-Lewis x expression and E-selectin adhesion. We assume that H-type alpha(1,2)-fucosyltransferase competes with the endogenous alpha(2,3)-sialyltransferase for the N-acetyllactosamine structures assigned to further serve as acceptors for alpha(1, 3)fucosyltransferase.

Circulating antibodies against an exocrine pancreatic enzyme in type 1 diabetes

In this article, we report the identification of a new autoantigen in type 1 diabetes originating from the exocrine pancreas. This antigen is a pancreatic enzyme termed bile salt-dependent lipase (BSDL). We show that antibodies present in the sera of newly diagnosed type 1 diabetic patients recognize BSDL and more specifically the COOH-terminal mucin-like region of the protein. Therefore, we engineered the COOH-terminal peptide of BSDL and demonstrated that autoreactivity was linked to specific glycosylation sites by at least two glycosyltransferases: the Core 2 beta(1-6)N-acetylglucosaminyltransferase and the alpha(1-3) fucosyltransferase FUT7. We next examined the prevalence of circulating anti-BSDL antibodies in type 1 diabetic patients and found 73.5% positivity (25 sera among 34 patients tested) at onset, whereas only 8.4% of normal individuals (7 of 83) were positive. Within a cohort of first-degree relatives of diabetic patients followed prospectively until development of diabetes, 6 of 19 (31.6%) were also positive. Interestingly, two prediabetic individuals were already positive for anti-BSDL antibodies (Abs), while islet cell cytoplasmic Abs and antibodies to GAD65, IA-2, and insulin were not detected. Anti-BSDL autoantibodies were weakly or not detected in patients suffering from pancreatitis or pancreatic adenocarcinoma or in patients with Graves' disease. Although autoreactivity to BSDL in prediabetic and newly diagnosed diabetic patients might reflect cross-reactivity, our results strongly suggest that in addition to pancreatic beta-cells, acinar cells may be also affected in type 1 diabetes.

The formation of the oncofetal J28 glycotope involves core-2 beta6-N-acetylglucosaminyltransferase and alpha3/4-fucosyltransferase activities

The feto-acinar pancreatic protein or FAPP, the oncofetal glycoisoform of bile salt-dependent lipase (BSDL), is characterized by the presence of the J28 glycotope recognized by mAbJ28. This fucosylated epitope is carried out by the O-linked glycans of the C-terminal mucin-like region of BSDL. This glycotope is expressed by human tumoral pancreatic tissues and by human pancreatic tumoral cell lines such as SOJ-6 and BxPC-3 cells. However, it is not expressed by the normal human pancreatic tissues and by MiaPaCa-2 and Panc-1 cells. Due to the presence of many putative sites for O-glycosylation on FAPP and BSDL, the structure of the J28 glycotope cannot be attained by classical physical methods. In the first part of the present study, we have determined which glycosyltransferases were differently expressed in pancreatic tumoral cell lines compared to normal tissues, focusing in part on fucosyltransferases (Fuc-T) and core-2 beta6-N-acetylglucosaminyltransferase (Core2GlcNAc-T). Our data suggested that alpha2-Fuc-T activity was decreased in the four cell lines tested (SOJ-6, BxPC-3, MiaPaCa-2, and Panc-1). The alpha(1-3) and alpha(1-4) fucosylations were decreased in tumor cells that do not express the J28 glycotope whereas alpha4-Fuc-T and Core2GlcNAc-T activities were significantly increased in SOJ-6 cells which best expressed the J28 glycotope. Therefore, we wished to gain information about glycosyltransferases involved in the building of this structure by transfecting the cDNA encoding the mucin-like region of BSDL in CHO-K1 also expressing Core2GlcNAc-T and/or FUT3 and/or FUT7 activities. These CHO-K1 cells have been previously transfected with the cDNA encoding Core2GlcNAc-T and/or FUT3 and/or FUT7. Data indicated that the C-terminal peptide of BSDL (Cter) produced by those cells did not carry out the J28 glycotope unless Core2GlcNAc-T activity is present. Further transfection with FUT3 cDNA, increased the antibody recognition. Nevertheless, transfection with FUT3 or FUT7 alone did not generate the formation of the J28 glycotope on the C-terminal peptide. Furthermore, the Cter peptide produced by CHO-K1 cells expressing Core2GlcNAc-T was more reactive to the mAbJ28 after in vitro fucosylation with the recombinant soluble form of FUT3. These data suggested that the J28 glycotope encompasses structures initiated by Core2GlcNAc-T and further fucosylated by alpha3/4-Fuc-T such as FUT3, likely on GlcNAc residues.

Immunodetection and molecular cloning of a bile-salt-dependent lipase isoform in HepG2 cells

In this article, we report the nucleotide sequence of the cDNA encoding an isoform of bile-salt-dependent lipase (BSDL) expressed by human hepatoma cells. The BSDL is a 100-kDa glycoprotein normally expressed by the human pancreas. Using a polyclonal antibody raised against an internal peptide located between Ile(327) and Glu(350) of the human pancreatic BSDL, we have immunodetected an isoform of human pancreatic BSDL, with an apparent molecular mass of about 62 kDa. This isoform of BSDL was mainly associated with the cytosol of a human hepatoma cell line (HepG2), the remaining protein being found in the microsome fraction. In addition, esterolytic activity on p-nitrophenyl hexanoate measured in microsomes and cytosol appeared very low and was weakly stimulated by bile salts, such as taurocholate. In contrast to human pancreatic BSDL, which is secreted as a component of pancreatic juice, this isoform appeared to be retained in the HepG2 cells. Reverse transcription, followed by PCR and amplification, performed on RNA extracted from HepG2 cells using specific primers hybridizing to the sequence coding for the entire normal human pancreatic BSDL, allowed us to amplify a 1. 7-kb transcript that appeared to be 0.5 kb shorter than the transcript of the pancreatic enzyme (2.2 kb). From the sequence of the transcript thus obtained, a protein with a molecular mass of 62 kDa might be predicted, which is in good agreement with the size of the isoform of BSDL immunodetected in HepG2 cells. The N-terminal amino-acid sequence, deduced from the 1.7-kb transcript sequence, matched that of the pancreatic BSDL. However, the C-terminal domain appeared truncated, bearing only a single mucin-like sequence compared with sixteen for the human pancreatic BSDL. The actual intracellular function of this human BSDL hepatoma isoform remains to be elucidated.

Hexamethylene bisacetamide (HMBA) increases thyroglobulin levels in porcine thyroid cells without increasing cyclic-AMP

The polar planar compound hexamethylene bisacetamide (HMBA) is an inducer of terminal differentiation which has been extensively studied in the murine erythroleukemia cells (MELC). We have tested this compound in normal porcine thyroid cells in primary culture where it either activates or inhibits the major tissue specific functions of these cells: it induces the reorganization of cells into follicles, prevents the loss of thyrotropin sensitivity in monolayer cells, activates cell growth but inhibits their iodide metabolism. In this paper, we demonstrate that HMBA acts on the total thyroglobulin levels measured in cell layers plus media. This specific marker of thyroid tissue is increased by HMBA both in kinetics and in concentration-response experiments. HMBA per se does not increase the total cyclic AMP measured either during the first hours after stimulation or in the following days when compared to controls. As expected, cyclic AMP in the same experiment increased rapidly within minutes after the cells were challenged by TSH (positive control). Altogether, the results show that the drug HMBA mimics thyrotropin effects on thyroglobulin levels measured in porcine thyroid cells in culture. This modulation cannot be explained by an increase in cyclic AMP, indicating that despite similarities between TSH and HMBA effects, the mechanism of the mode of action of these two molecules is very different.

Predictive validity of the Young Offender Level of Service Inventory for criminal recidivism of male and female young offenders

164 male and female young offenders were given the Young Offender Level of Service Inventory. Scores from this 76-item risk assessment were used to produce a matched sample of 82 female and 82 male young offenders. Sex did not influence the 1-yr, criminal recidivism rate, a result consistent with other findings.

Green fluorescent protein-based system for analysis of E-selectin-mediated adhesion

Numerous cell-based or cell-free systems for study of selectin adhesion use radiolabeled tracers. However, in addition to handling problems associated with the use of radioisotopes, these assays have difficulty relating a number of counts to a number of adherent cells. Here, we describe an assay that uses the natural fluorescence of the green fluorescent protein (GFP) to measure binding of cells to E-selectin. We elaborated an adhesion system composed of a cell monolayer expressing E-selectin ligand to which monodispersed fluorescent Chinese hamster ovary (CHO) cells expressing E-selectin are added. Due to GFP autofluorescence, adhered cells can be easily distinguished from cell monolayers by fluorescence microscopy, and adhesion can be measured by cytofluorometry. We applied this GFP-based adhesion assay to measure the adherence of a pancreatic tumor cell line and found that the binding parameters of these cells satisfy a number of E-selectin-specific criteria.

Molecular cloning of the oncofetal isoform of the human pancreatic bile salt-dependent lipase

Specific transcripts for bile salt-dependent lipase (BSDL), a 100-kDa glycoprotein secreted by the human pancreas, were immunodetected in BxPC-3 and SOJ-6 pancreatic tumoral cell lines. Sequencing of fragments, obtained by mRNA reverse transcription and amplification, confirmed the presence of BSDL transcripts in these cancer cells. The protein was detected in lysates of pancreatic tumoral cells, where it was mainly associated with membranes. Only a minute amount of the enzyme was detected in the culture media. Immunofluorescence studies demonstrated that in SOJ-6 cells, BSDL colocates with the p58 Golgi protein and suggested that the protein may be sequestrated within the Golgi compartment. These results demonstrated that BSDL is expressed in human pancreatic tumoral cells and cannot be secreted (or for the least very poorly). Subsequently, a cDNA covering the entire sequence of BSDL was obtained by reverse transcription-polymerase chain reaction. The sequence of this cDNA indicated that the N-terminal domain encoded by exons 1-10 was identical to that of BSDL expressed by the human normal pancreas. However, the sequence corresponding to exon 11, which should code for the 16 tandem-repeated identical mucin-like sequences of BSDL, was deleted by 330 base pairs (bp) and encoded only 6 of these repeated sequences. We conclude that this truncated variant of BSDL would be its oncofetal form, referred to as feto-acinar pancreatic protein. We then investigated whether the deletion of 330 bp affected the secretion of the protein. For this purpose, the cDNA corresponding to the mature form of the BSDL variant expressed in SOJ-6 cells was cloned into an expression/secretion vector and transfected into CHO-K1 cells. Results indicated that the variant of BSDL isolated from SOJ-6 cells was expressed and secreted by transfected cells. However, the level of BSDL secreted by these transfected CHO-K1 cells was significantly higher than that observed for SOJ-6 cells. Consequently, the retention of the oncofetal variant of BSDL observed in human pancreatic tumoral cells might not result from inherent properties of the protein.

Effects of ethanol on the expression and secretion of bile salt-dependent lipase by pancreatic AR4-2J cells

The mechanisms by which ethanol administration alters pancreatic function are unknown. We have evaluated the effects of chronic ethanol treatment on secretion of a digestive enzyme: the bile salt-dependent lipase (BSDL), by the rat pancreatic cell line AR4-2J (as a model). We report that ethanol (50-300 mM) in culture medium induced a rise, in secreted and intracellular BSDL, that was a function of the duration of treatment and of the ethanol concentration. This effect was not abolished by pyrazole, which suggests a direct effect of ethanol. We have further established that the increase of BSDL activity was due to an enhanced biosynthesis of the enzyme consecutive to a major steady-state level of mRNA encoding BSDL. Also, the subcellular localization showed a specific accumulation of BSDL in the cytosolic fraction of cells chronically treated with ethanol. Given the enzymatic properties of BSDL, all these data could have some physiological consequences regarding the digestive function, plasma lipid metabolism and intracellular cholesterol homeostasis.

Participation of GRP94-related protein in secretion of pancreatic bile salt-dependent lipase and in its internalization by the intestinal epithelium

In previous studies on the AR4-2J cell line, we have shown that secretion of bile salt-dependent lipase (BSDL) involves a multiprotein complex, including a protein of 94 kDa (p94) that is immunologically related to the chaperone Grp94, which seems to play essential roles in the folding process of BSDL. Combined biochemical and immunocytochemical investigations were carried out to study the secretion of BSDL by normal pancreatic cells and its transport to the small intestine where this enzyme is thought to exert its physiological function. Both BSDL and Grp94 antigenic sites were localized and found to be associated all along the pancreatic acinar cell secretory pathway. Grp94 and BSDL remain associated from leaving the pancreas until arriving at the intestinal lumen. In pancreatic juice, both proteins appear as a complex of high molecular mass (180 kDa) containing at least one each of p94 and BSDL molecules, interacting by hydrophobic forces. At the intestinal level, associated Grp94 and BSDL were detected on microvilli and in the endosomal compartment of enterocytes. The BSDL mRNA, however, was not expressed by the intestinal mucosa. The pancreatic Grp94-BSDL complex was internalized through the endosomal compartment of enterocytes. Finally, the two proteins dissociated in this compartment and BSDL, but not Grp94, was transferred to the basolateral membrane.

An intracellular role for pancreatic bile salt-dependent lipase: evidence for modification of lipid turnover in transfected CHO cells

Pancreatic bile salt-dependent lipase (BSDL) hydrolyzes cholesteryl esters, triglycerides and phospholipids. BSDL is also capable of transferring free fatty acid to cholesterol. BSDL has been detected in many cells including fetal and tumor cells, hepatocytes, macrophages and eosinophils and in tissues such as adrenal glands and testes. The enzyme may be secreted or located within subcellular compartments such as the endoplasmic reticulum or the cytosol. Although the role of the secreted enzyme is well documented, that of the intracellular form(s) is still hypothetical. In the present study, we addressed the effects of BSDL on cell lipid metabolism. For that purpose, the cDNA of rat BSDL was transfected into CHO K1 cells (CHO K1-BSDL clone) which were then loaded with [3H]oleic acid. The results demonstrate that the transfected BSDL is secreted; in spite of that, a large fraction of catalytically active BSDL is found in cell lysate. The lipid metabolism of transfected cells is affected and BSDL induces an enhanced incorporation of [3H]oleic acid in cholesteryl esters whereas fatty acid incorporation in phosphatidylcholine is decreased. These effects were particularly important in the cytosol of transfected cells where transfected BSDL preferentially locates. These data suggested that BSDL could be implicated in the cycle of the cellular homeostasis of cholesterol which is particularly affected in tumoral cells leading to cholesteryl ester storage within cytosolic lipid droplets.

Molecular cloning of the bile salt-dependent lipase of ferret lactating mammary gland: an overview of functional residues

Ferret lactating mammary gland bile salt-dependent lipase (BSDL, EC 3.1.1.-) has been cloned by RT-PCR. The open reading frame consists of 1869 nucleotides which encode 623 amino acids of the functional enzyme. When compared to other species, the greatest homology is observed between residues 1 and 484, with little or no homology at the C-terminal end where seven repeated segments of similar sequence are located. Ferret mammary gland BSDL retains residues involved in the active site and the tentative heparin binding site at similar positions in comparison to other milk or pancreatic BSDL. Other important items, such as binding peptide to chaperone molecular, phosphorylation site(s) or bile salt binding sites, were also tentatively located in well conserved regions of seven available BSDL sequences.

Functional reconstitution of membrane glycoproteins into lipid vesicles using lectin precipitation. Application to the VIP receptor

We studied the interaction of n-octyl-beta-d-glucopyranoside-solubilized VIP receptors (VIPR) with wheat germ agglutinin and found that the addition of the lectin to the detergent extract led to the formation of aggregates that could be pelleted by high speed centrifugation. Resuspension of the pellet in the presence of the competing trisaccharide, N,N', N"-triacetylchitotriose (TAC), dissociated the lectin from the complex without altering the precipitability of VIPR. The final pellet (referred to as TAC pellet) contained an average of 12% of total protein and 96% of total VIP binding activity with a typical rank order of potency for VIP-related peptides. Lipid analysis and electron microscopic examination indicated that the precipitated material was composed of lipid vesicles. VIPR molecules were shown to be integrally inserted in the liposomes because they could not be dissociated from the vesicles at pH 11 or with high salt concentration. By comparing the liposome-associated VIP binding activity in the presence and absence of detergent and by showing accessibility of VIPR to PNGase F, it was concluded that VIP binding sites were not simply trapped within the reconstituted vesicles but likely exposed at the external surface of the liposomes.

Fucosyltransferase activities in human pancreatic tissue: comparative study between cancer tissues and established tumoral cell lines

Human pancreatic cancer is characterized by an alteration in fucose-containing surface blood group antigens such as H antigen, Lewis b, Lewis y, and sialyl-Lewis. These carbohydrate determinants can be synthesized by sequential action of alpha(2,3) sialyltransferases or alpha(1,2) fucosyltransferases (Fuc-T) and alpha(1,3/1,4) fucosyltransferases on (poly)N-acetyllactosamine chains. Therefore, the expression and the function of seven fucosyltransferases were investigated in normal and cancer pancreatic tissues and in four pancreatic carcinoma cell lines. Transcripts of FUT1, FUT2, FUT3, FUT4, FUT5, and FUT7 were detected by RT-PCR in carcinoma cell lines as well as in normal and tumoral tissues. Interestingly, the FUT6 message was only detected in tumoral tissues. Analysis of the acceptor substrate specificity for fucosyltransferases indicated that alpha(1,2) Fuc-T, alpha(1,3) Fuc-T, and alpha(1,4) Fuc-T were expressed in microsome preparations of all tissues as demonstrated by fucose incorporation into phenyl beta-d-galactoside, 2'-fucosyllactose, N-acetyllactosamine, 3'-sialyl-N-acetyllactosamine, and lacto-N-biose. However, these fucosyltransferase activities varied between tissues. A substantial decrease of alpha(1,2) Fuc-T activity was observed in tumoral tissues and cell lines compared to normal tissues. Conversely, the activity of alpha(1,4) Fuc-T, which generates Lewis a and sialyl-Lewis a structures, and that of alpha(1,3) Fuc-T, able to generate a lactodifucotetraose structure, were very important in SOJ-6 and BxPC-3 cell lines. These increases correlated with an enhanced expression of Lewis a, sialyl-Lewis a, and Lewis y on the cell surface. The activity of alpha(1,3) Fuc-T, which participates in the synthesis of the sialyl-Lewis x structure, was not significantly modified in cell lines compared to normal tissues. However, the sialyl-Lewis x antigen was expressed preferentially on the surface of SOJ-6 and BxPC-3 cell lines but was not detected on Panc-1 and MiaPaca-2 cell lines suggesting that several alpha(1,3) Fuc-T might be involved in sialyl-Lewis x synthesis.

Pancreatic bile-salt-dependent lipase activity in serum of diabetic patients: is there a relationship with glycation?

1. Pancreatic bile-salt-dependent lipase has been detected in human plasma where it has the capability to modify normal low- and high-density lipoprotein composition and structure and to reduce the atherogenicity of oxidized low-density lipoprotein (Shamir R, Johnson WJ, Morlock-Fitzpatrick K, Zolfaghari R, Li L, Mas E, Lombardo D, Morel DW, Fisher EA. Pancreatic carboxyl ester lipase: a circulating enzyme that modifies normal and oxidized lipoproteins in vitro. J Clin Invest 1996; 97: 1696-704). 2. In the present study, we investigated the effect of glycation and particularly that of human serum albumin on the activity of bile-salt-dependent lipase. In vitro, bile-salt-dependent lipase activity decreased in the presence of human serum albumin; however, this was less pronounced in the presence of glycated human serum albumin. In vivo, bile-salt-dependent lipase specific activity was about 2-fold higher in the sera of diabetic patients than in the sera of normal subjects. 3. A significant increase in the specific activity of bile-salt-dependent lipase related to the serum level of glycation was observed. The increase in bile-salt-dependent lipase specific activity was not related to the glucose concentration in serum suggesting that glycation of bile-salt-dependent lipase could not be involved in the observed effects. Although the stability of serum bile-salt-dependent lipase was important enough to allow a systemic action of the enzyme on lipoproteins, it could not explain the higher activity of the enzyme in diabetic serum. 4. We concluded that bile-salt-dependent lipase could be helpful against the premature development of atherosclerosis in diabetes.

Pedunculated liposarcoma of the esophagus

Polypoid tumors of the esophagus present diagnostic and therapeutic problems. Liposarcomas are infrequent among them. We report a recent case. A 73-year-old male patient was seen in May 1995 in the Ear, Nose and Throat (ENT) Department, Clínica Modelo de Morón, with intermittent dysphagia and dyspnoea due to recurrent vomiting. A laryngeal lineal tomography showed a subglottic obstruction due to extrinsic compression. The patient was referred to the Gastroenterology Department, where an upper gastrointestinal (upper GI) series demonstrated mega-esophagus with abundant retained food. Endoscopy showed a large intraluminal mass covered by normal mucosa which arose on the posterior wall. Videofluoroscopy and chest CT diagnosed a probable polypoid lipoma due to its densitometric characteristics. The tumour was resected by left cervicotomy and left esophagotomy. The patient's progress to date is favourable. Pathology studies showed a well-differentiated liposarcoma. According to the literature, the first case was reported in 1983, and ours is only the seventh case in the world to be documented.

Pancreatic bile salt-dependent lipase activity in serum of normolipidemic patients

Bile salt-dependent lipase (BSDL, E.C. 3.1.1.-) is a digestive enzyme secreted by the pancreatic acinar cell. Once in the duodenum, the enzyme, upon activation by primary bile salts, hydrolyzes dietary lipid esters such as cholesteryl esters and lipid-soluble vitamin esters. This enzyme is partially transferred from the duodenum or pancreas to the circulation where it has been postulated to exert a systemic action on atheroma-generating oxidized-low density lipoprotein (LDL). In the present study, sera from 40 healthy normolipidemic volunteers were used to investigate the possible linkage between circulating BSDL, lipids, and lipoproteins. We showed, firstly, that pancreatic-like BSDL activity can be detected in these serums. Secondly, BSDL activity increased significantly with the level of LDL-cholesterol and was also positively linked to the serum concentration of Apo B100 and Apo A-I. Thirdly, we also established that BSDL was associated with LDL, in part by a specific interaction with Apo B100, while no interaction was found with Apo A-I. No linkage with other recorded parameters (triglycerides, phospholipids, and high density lipoprotein-cholesterol) was detected. Because an increase in LDL-cholesterol represents an important risk factor for atheroma, the concomitant increase in BSDL, which can metabolize atherogenic LDL, suggests for the first time that this circulating enzyme may exert a positive effect against atherosclerosis.

O-Glycosylation of C-terminal tandem-repeated sequences regulates the secretion of rat pancreatic bile salt-dependent lipase

Amino acid sequences rich in Pro, Glu, Ser, and Thr (PEST) are common to rapidly degraded proteins (Rogers, S., Wells, R. & Rechsteiner, M. (1986) Science 234, 364-368). On pancreatic bile salt-dependent lipase (BSDL), PEST sequences are present in the C-terminal region of the enzyme to which is associated the O-glycosylation. We have postulated that the O-glycosylation of BSDL may contribute to mask PEST sequences and to trigger the secretion of this enzyme instead of its delivery into a degradative pathway (Bruneau, N., and Lombardo, D. (1995) J. Biol. Chem. 270, 13524-13523). To further examine the role of the O-linked glycosylation on BSDL metabolism, rat pancreatic BSDL cDNA was stably transfected into two Chinese hamster ovary (CHO) cell lines, the CHO K1 wild-type line and the O-glycosylation defective CHO ldlD line. In these latter cells, O-glycosylation can be reversibly modulated by culture conditions. Results indicate that the rate of BSDL synthesis by transfected CHO K1 or CHO ldlD cells reflects, independently of culture conditions, the amount of mRNA specific for BSDL present in these transfected cells. Nevertheless, the rate of secretion of the enzyme depends upon cell culture conditions and increases with the cell capability to O-glycosylate C-terminal tandem-repeated sequences. Immunoprecipitation experiments performed on cell lysates suggested that a rapid degradation of BSDL occurred particularly when transfected CHO ldlD cells were cultured under non-permissive conditions. We further showed that BSDL secreted by CHO ldlD cells grown under non-permissive conditions that normally prevent O-glycosylation incorporated galactose and was reactive with peanut agglutinin, which recognizes the core structure of O-linked glycans. We concluded that the BSDL expressed by CHO ldlD cells grown under non-permissive conditions was rapidly degraded but a fraction of the enzyme was allowed to O-glycosylate and consequently was secreted.

Association of bile-salt-dependent lipase with membranes of human pancreatic microsomes is under the control of ATP and phosphorylation

Bile-salt-dependent lipase (BSDL) is secreted by the pancreas into the duodenum, where it catalyses the hydrolysis of dietary lipid esters on activation by bile salts. The secretion pathway of BSDL is comparable with that of other digestive enzymes produced by pancreatic acinar cells. However, in contrast with these other enzymes, BSDL is partly associated with endoplasmic reticulum membranes as part of a folding complex, including a Grp94-related protein to which BSDL is transiently linked. The release of BSDL from membranes occurs once its glycosylation is completed [Bruneau and Lombardo (1995) J. Biol. Chem. 270, 13524-13533]. In the present study, investigations concerning the mechanism of association/dissociation of BSDL with membranes of microsomes were performed. For this purpose the role of ATP and that of the possible phosphorylation of BSDL were examined. For the first time, it is shown that human pancreatic BSDL is phosphorylated, probably at a serine residue, during its transport within the acinar cell. The phosphorylation of BSDL is provoked by calphostin C, an inhibitor of protein kinase C. In the presence of 1-(isoquinolinesulphonyl)2-methylpiperazine, a non-specific inhibitor of serine/threonine protein kinase A, C or G, or of calcium chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N', N'-tetra-acetic tetra(acetoxymethyl)ester, the phosphorylation of BSDL elicited by calphostin C is abolished. These data suggested that the phosphorylation of BSDL within human pancreatic microsomes is under the control of a cascade of protein kinases. We have also shown that the phosphorylation of BSDL appears to be involved in the release of the enzyme from microsome membranes. Nevertheless ATP, which modifies the conformation of BSDL, triggers this association, and an unhydrolysable ATP analogue was unable to promote it.

Performance and First Results of the ELETTRA High-Flux Beamline for Small-Angle X-ray Scattering

A new beamline for small-angle X-ray scattering (SAXS) has recently been constructed and is presently under final commissioning at the 2 GeV storage ring ELETTRA. It has been designed specifically for time-resolved studies of non-crystalline and fibrous materials and has been optimized for small-angle scattering measurements. The beamline operates with a SAXS resolution between 10 and about 1400 Å in d spacing (at 8 keV) and has been optimized with respect to high flux at the sample [of the order of 1013 photons s−1 for 8 keV photons (2 GeV, 400 mA)]. Soon it will be possible to perform simultaneously wide-angle diffraction measurements in the d-spacing range 1.2–8 Å (at 8 keV). In order to allow time-resolved (resolution ~1 ms) small-angle scattering measurements, a high-power 57-pole wiggler is used as the beamline source. From its beam, one of three discrete energies, 5.4, 8 and 16 keV, can be selected with a double-crystal monochromator, which contains three pairs of asymmetrically cut plane Si(111) crystals. Downstream, the beam is focused horizontally and vertically by a toroidal mirror. Commissioning tests of this new SAXS beamline showed that all design parameters have been realized.

The oncofetal J28 epitope involves fucosylated O-linked oligosaccharide structures of the fetoacinar pancreatic protein

The fetoacinar pancreatic protein (FAP), characterized by the mAb J28, is an oncofetal form of bile salt dependent lipase (BSDL), the expression of which is related to pancreatic differentiation and neoplastic processes. Because the J28 epitope, recognized by mAb J28, is suggested to be dependent upon carbohydrates, we have attempted to gain information about the structure of this epitope. Indeed, treatment of FAP with sodium periodate abolished the reactivity of the protein to mAb J28, which demonstrates the implication of oligosaccharides in the structure of the J28 epitope. FAP offers both O-linked and N-linked carbohydrate structures, of which, as we have determined, one is involved. Peptides obtained after cyanogen bromide cleavage were desialylated then separated by affinity chromatography on an immobilized peanut agglutinin agarose column. The peptide retained on this column carried out the reactivity with the mAb J28. Although some differences in amino acid analysis were observed, the N-terminal sequence of this peptide correlates with that of the C-terminal part of the enzyme. Carbohydrate analysis of the peptide bearing the J28 epitope revealed fucose, galactose, N-acetylgalactosamine, N-acetylglucosamine, and N-acetylneuraminic acid. The competition observed between mAb J28 and Ulex europaeus I lectin for binding to the J28 epitope suggested that fucose residue alpha (1-2) linked to a galactose residue was implicated in the structure of the J28 epitope. Alternatively, the loss of the mAb J28 reactivity upon treatment of FAP either with bovine kidney or bovine epididymis fucosidase was observed indicating that fucose residues linked at the alpha (1-2) and alpha (1-6) positions may be involved in the establishment of the structure of the J28 epitope. These observations suggest that mAb J28 recognized a particular fucosylated O-linked oligosaccharide structure located at the mucin-like extended C-terminal part of FAP.

Investigation of two glycosylated forms of bile-salt-dependent lipase in human pancreatic juice

Pure human pancreatic bile-salt-dependent lipase, devoid of its oncofetal glycoform [Mas, E., Abouakil, N., Roudani, S., Miralles, F., Guy-Crotte., O., Figarella, C., Escribano, M. J. & Lombardo, D. (1993) Biochem. J. 289, 609-615], was analyzed on immobilized concanavalin A (ConA). Two variants were separated: an unabsorbed ConA-unreactive fraction; and an absorbed ConA-reactive fraction. Carbohydrate compositions of ConA-reactive and ConA-unreactive fractions were not significantly different, and analysis of 3H-labelled oligosaccharides liberated from these fractions on the ConA-Sepharose column indicated that the fractionation of the bile-salt-dependent lipase on this column depends upon oligosaccharide structures. The activity of the ConA-reactive fraction was however much lower, independent of the substrate (4-nitrophenyl hexanoate or cholesteryl esters), than that of the ConA-unreactive fraction. Therefore, catalytic constants for the hydrolysis of 4-nitrophenyl hexanoate were determined; both fractions had quite similar Km, while the kcat for the ConA-unreactive fraction was 3-4-fold higher than that of the ConA-reactive fraction. ConA-reactive and ConA-unreactive fractions were shown to have slightly different molecular masses and different amino acid compositions. Cleavage patterns after cyanogen bromide treatment of the ConA-reactive and ConA-unreactive fractions suggested that the ConA-reactive (high Mr form) and ConA-unreactive (low Mr form) forms could be different isoforms of the bile-salt-dependent lipase secreted by the human pancreas.

Digestive lipases of the newborn ferret: compensatory role of milk bile salt-dependent lipase

The amount of mRNA hybridizing to bile salt-dependent lipase and to colipase-dependent lipase probes as well as their translation into active proteins were quantified in the adult and newborn pancreas and lactating mammary gland from the ferret, a species whose milk, similar to that of the human, has bile salt-dependent lipase. The concentration of colipase-dependent lipase mRNA correlated with the amount of activity found in the adult and newborn pancreas, whereas neither mRNA nor activity of this enzyme was detected in the kit pancreas or in the lactating mammary gland. These data indicate that colipase-dependent lipase is actually expressed in adult pancreas and might represent the main lipolytic system in the adult. mRNA hybridizing to the bile salt-dependent lipase probe used in this study were detected in adult and in newborn ferret pancreas as well as in lactating mammary gland. However, the bile salt-dependent lipase activity expressed in the newborn pancreas was very low when compared with the activity expressed either in the mammary gland or in the adult pancreas. These data argue for a compensatory role of milk bile salt-dependent lipase in lipid digestion in the newborn. The hydrolysis of dietary fat might be initiated by preduodenal lipase, the activity of which is only two times lower in the gastric mucosa of the newborn than in the adult ferret. The high concentration of mRNA hybridizing to the bile salt-dependent lipase probe associated with a very poor bile salt-dependent lipase activity and protein suggests either that these mRNA are very unstable or that they are poorly translated into an active pancreatic bile salt-dependent lipase.

Pancreatic carboxyl ester lipase: a circulating enzyme that modifies normal and oxidized lipoproteins in vitro

Pancreatic carboxyl ester lipase (CEL) hydrolyzes cholesteryl esters (CE), triglycerides (TG), and lysophospholipids, with CE and TG hydrolysis stimulated by cholate. Originally thought to be confined to the gastrointestinal system, CEL has been reported in the plasma of humans and other mammals, implying its potential in vivo to modify lipids associated with LDL, HDL (CE, TG), and oxidized LDL (lysophosphatidylcholine, lysoPC). We measured the concentration of CEL in human plasma as 1.2+/-0.5 ng/ml (in the range reported for lipoprotein lipase). Human LDL and HDL3 reconstituted with radiolabeled lipids were incubated with purified porcine CEL without or with cholate (10 or 100 microM, concentrations achievable in systemic or portal plasma, respectively). Using a saturating concentration of lipoprotein-associated CE (4 microM), with increasing cholate concentration there was an increase in the hydrolysis of LDL- and HDL3-CE; at 100 microM cholate, the present hydrolysis per hour was 32+/-2 and 1.6+/-0.1, respectively, indicating that CEL interaction varied with lipoprotein class. HDL3-TG hydrolysis was also observed, but was only approximately 5-10% of that for HDL3-CE at either 10 or 100 microM cholate. Oxidized LDL (OxLDL) is enriched with lysoPC, a proatherogenic compound. After a 4-h incubation with CEL, the lysoPC content of OxLDL was depleted 57%. Colocalization of CEL in the vicinity of OxLDL formation was supported by demonstrating in human aortic homogenate a cholate-stimulated cholesteryl ester hydrolytic activity inhibited by anti-human CEL IgG. We conclude that CEL has the capability to modify normal human LDL and HDL composition and structure and to reduce the atherogenicity of OxLDL by decreasing its lysoPC content.

Recombinant human dihydroorotate dehydrogenase: expression, purification, and characterization of a catalytically functional truncated enzyme

An N-terminally truncated cDNA for human dihydroorotate dehydrogenase (DHODase) was placed under the control of the inducible T7 lac promoter in a pyrimidine auxotrophic strain of Escherichia coli lacking the endogenous enzyme. Induction of gene expression rescued growth in media lacking exogenous pyrimidines. The recombinant enzyme was purified to homogeneity from detergent extracts of bacterial membranes by two chromatographic steps. The purity of the resulting enzyme was judged to be > 95% based on SDS-PAGE with Coomassie staining. The enzyme displays an apparent molecular weight of ca. 40 kDa on SDS-PAGE and ca. 120 kDa on native size-exclusion chromatography, suggesting that the native enzyme is multimeric. Recombinant DHODase displayed a specific activity and Km for dihydroorotate that were similar to those for the enzymes from bovine and human liver tissue. The pH dependence of the activity of the recombinant enzyme was likewise similar to that of the enzyme from human liver and may indicate the involvement of a critical histidine residue in catalytic turnover; only eight histidine residues remain in the truncated version of DHODase used here. The catalytic activity of the recombinant enzyme is inhibited in a dose-dependent fashion by the histidine-selective modifying agent diethylpyrocarbonate. These results further suggest a potential role for histidine in enzyme turnover. Brequinar sodium, an experimental drug which has been shown to be a nanomolar noncompetitive inhibitor of mammalian DHODases, inhibited the activity of the purified recombinant enzyme with a Ki value similar to that for enzyme derived from human liver tissue. The recombinant DHODase thus displays enzymatic behavior similar to the 50-kDa full-length human liver enzyme, illustrating that the catalytically essential structural features of the enzyme, as well as the site of Brequinar binding, are contained within the 40-kDa truncated version of the enzyme that was expressed here.

Bile salt-dependent lipase transcripts in human fetal tissues

In human fetal pancreas, we identified two cDNA transcripts of the bile salt-dependent lipase (BSDL) using reverse transcription followed by polymerase chain reaction (RT-PCR). The sequence of four overlapping segments obtained by RT-PCR matched the sequence of the 2.2 kb cDNA cloned from human adult pancreas (Reue et al. (1991) J. Lipid Res. 32, 267-276). A second RT-PCR product of approx. 1.1 kb was evidenced, the sequence of which corresponds to that of the BSDL-pseudogene transcript (Nilsson et al. (1993) Genomics, 17, 416-422). The short transcript is present in all tissues examined whereas the former one (2.2 kb) is either poorly (in liver and kidney) or not at all expressed in adult tissues, excepted in the pancreas. On the other hand, the 2.2 kb transcript specific of the BSDL gene was detected in all fetal tissues examined as early as the 6th week of gestation. Results also suggested that the fetal pancreas contains more 2.2 kb transcript than its adult counterpart. Therewith, BSDL was immuno-precipitated from fetal liver. The role of BSDL-gene expression during the fetal life is discussed.

Association of bile-salt-dependent lipase with membranes of human pancreatic microsomes

Immunolocalization studies indicated that, in contrast to other enzyme markers of human pancreatic secretion, bile-salt-dependent lipase (BSDL) was partly but specifically associated with endoplasmic reticulum membranes. In microsomes, temperature-induced phase separation using Triton X-114 elucidated the partition of BSDL between the aqueous phase and the detergent-rich phase containing hydrophilic and membrane proteins, respectively. The size of the membrane-associated BSDL (approx. 100 kDa) is compatible with that of the fully processed enzyme. Fucosylated O- and N-linked oligosaccharide structures were detected by means of specific lectins. The membrane-associated BSDL might therefore be released from membranes between the trans-Golgi compartment (where terminal fucose residues were added) and the zymogen granules where BSDL was mainly found in the soluble fraction. Even though BSDL associated with membranes was enzymically active, it appeared less efficient than the soluble form. The association of BSDL with membranes was pH-dependent and optimal association occurred between pH 5-6. The membrane-associated BSDL was released by KBr which suggests that the association of BSDL with microsomal membranes involves ionic interactions. Lipid-protein interactions are probably not involved in this association as BSDL did not associate with liver microsome membranes. We attempted to characterize the putative ligand and showed that BSDL and a 94-kDa protein, immunologically related to a glucose-regulated protein of 94 kDa (Grp94), were co-immunoprecipitated by specific antibodies directed against each individual species. It is suggested that the biogenesis of the human pancreatic BSDL involves an association with intracellular membranes and that its folding may be assisted by molecular chaperones.

Chaperone function of a Grp 94-related protein for folding and transport of the pancreatic bile salt-dependent lipase

In its fundamental attributes, the secretion pathway of the pancreatic bile salt-dependent lipase (BSDL) followed that described for all enzymes involved in regulated secretion. This route was inhibited by drugs that affect protein synthesis and intracellular transport. In the presence of monensin, BSDL was solely detected in microsome membrane fractions. The association of BSDL with intracellular membranes involved a protein complex, formed by at least two proteins of 94 and 56 kDa. In cells experiencing the metabolic stress due to azetidine-2-carboxylic acid, BSDL was additionally associated with a protein of 46 kDa. Affinity blotting showed that BSDL bound directly to the 94-kDa protein (p94). It was suggested that p94 could be a molecular chaperone, further identified as related to the 94-kDa glucose regulated protein (Grp 94). The membrane-associated BSDL (i.e. BSDL bound to the Grp 94-related p94) was O- and N-glycosylated and consequently appeared released from membranes in the trans-Golgi compartment. Therefore and for the first time, it is suggested that a multiprotein complex including the chaperone Grp 94-related p94 protein may play an essential role in the folding and transport of BSDL. One hypothesis is that the association of BSDL with membrane via the Grp 94-related p94 along its secretion pathway is required for its complete O-glycosylation, which occurs on the extended mucin-like structures present on the C-terminal part of the protein.

Expression of a 46 kDa protein in human pancreatic tumors and its possible relationship with the bile salt-dependent lipase

Bile salt-dependent lipase (BSDL), an enzyme normally found in human pancreatic secretions is a 100 kDa glycoprotein. A BSDL-specific 477 bp cDNA probe was prepared by performing polymerase chain reaction experiments. This cDNA was used to probe mRNAs extracted from human pancreatic tissue and tumoral cell lines. Two mRNAs were detected in normal human pancreas at 2.2 and 1.3 to 1.5 kb. In human pancreatic tumoral cells, mRNAs encoding for the BSDL were detected using in situ hybridization, and proteins with an M(r) of 46,000 to 48,000 were translated into an in vitro system using mRNAs extracted from these cells. Using an immunoprecipitation procedure, we observed here that the specific BSDL polyclonal antibodies recognized three proteins of 100 +/- 5 (p100), 46 +/- 2 (p46) and 22.7 +/- 1.2 (p23) kDa, respectively in the soluble extracts of normal adult human pancreas. The p100 protein was probably the glycosylated product resulting from the translation of the 2.2 kb transcript. The p46 protein, which electrophoresed as a doublet was the main component immunoprecipitated from extract of a differentiated human pancreatic adenocarcinoma as well as from the extracts of two pancreatic cell lines, BxPC-3 and SOJ-6. In addition, the p46 immunoform of the BSDL was detected in cell-free medium from SOJ-6 cell line and its expression was found to be correlated with the secretion of an esterolytic activity on 4-nitrophenyl caproate, whereas the BxPC-3 cell line neither secreted the p46 nor showed any esterolytic activity on this substrate. The p46 may be either a short variant of BSDL resulting from the translation of the 1.3 to 1.5 kb transcript or a protein structurally related to the enzyme. The p46 doublet immunoform was detected in the human pancreatic secretion.

Horse pancreatic lipase. The crystal structure refined at 2.3 A resolution

Pancreatic lipase (EC 3.1.1.3) plays a key role in dietary fat digestion by converting triacylglycerols into 2-monoacylglycerols and free fatty acids in the intestine. Although the crystallographic structures of the human pancreatic lipase and of a human lipase-porcine colipase complex have been solved, no refined structure of pancreatic lipase has yet been published. The crystal structure of the horse enzyme was solved by the molecular replacement method from the model of the human pancreatic lipase and subsequently refined to 2.3 A resolution. The final model contains two molecules of 449 amino acid residues each in the asymmetric unit, 705 well-defined water molecules and two calcium ions. The two molecules in the asymmetric unit of the orthorhombic crystals are related by a 2-fold non-crystallographic symmetry axis as in the case of the human lipase. However, the association between the two molecules in their respective crystal forms is different. The overall molecular structure of the horse lipase is very similar to that of the human enzyme. The horse lipase is made up of two well-defined domains. The N-terminal domain which bears the active centre has a typical alpha/beta hydrolase fold topology. The C-terminal domain which is devoted to colipase binding has a beta-sheet sandwich topology. Comparison of equivalent C alpha atom positions between the final model of the horse lipase and the human lipase structure shows only slight differences which are mainly located in the C-terminal domain. The horse enzyme possesses the common features of the known mammalian and microbial lipases, in particular the "flap" covering the catalytic triad. In addition to more precise information concerning these features, the elucidation of the horse lipase crystal structure allowed us to better understand the structural basis of the kinetic behaviour of pancreatic lipases towards a soluble substrate, p-nitrophenyl acetate, and the different sensitivity of these enzymes towards limited proteolysis.

Efficacy and safety evaluation of lacidipine compared with amlodipine in mild-to-moderate hypertensive patients

Hypertension is well recognized to be an important cardiovascular risk factor and antihypertensive therapy has been shown to decrease cardiovascular mortality and morbidity as blood pressure control is achieved. At present, management of hypertension is obtained with effective compounds that exhibit a satisfactory safety profile. Among the antihypertensive drugs, calcium antagonists have been proven to possess this property. In the present study, our objective was to compare the antihypertensive effect of two new long-acting dihydropyridines, lacidipine and amlodipine, as once-daily monotherapies in mild-to-moderate hypertensive patients. Eighty hypertensive patients were recruited and after a 3-week washout period were randomized to receive lacidipine 4 mg once daily or amlodipine 10 mg once daily. After 4 weeks, hydrochlorothiazide 12.5 mg was added in patients not adequately controlled, and patients were treated for a total of 8 weeks. At this time, supine mean diastolic blood pressure decrease was 16 mm Hg in the lacidipine group and 10 mm Hg in the amlodipine group (p < = 0.01). Adverse events were reported in 28% of patients treated with lacidipine and in 48% of patients receiving amlodipine. Results of our pilot clinical experience show that lacidipine is a well-tolerated and effective compound, compared with amlodipine, in mild-to-moderate hypertensive patients.

Bile salt-dependent lipase biosynthesis in rat pancreatic AR 4-2 J cells. Essential requirement of N-linked oligosaccharide for secretion and expression of a fully active enzyme

This study used the rat pancreatic AR 4-2 J cell line as a model system to investigate the role of glycosylation in bile salt-dependent lipase (BSDL) secretion and esterolytic activity. Results indicated that AR 4-2 J cells synthesized BSDL, the esterolytic activity of which was the greater part of the cell activity toward 4-nitrophenylcaproate. The protein thus expressed was glycosylated and had a molecular mass approximately 74 kDa. Exposure of these cells to tunicamycin significantly decreased [3H]mannose incorporation, while [35S]methionine incorporation in trichloroacetic acid-precipitable material was not modified. Tunicamycin treatment of AR 4-2 J cells lead to a lower molecular mass form (approximately 70 kDa) of BSDL which did not incorporate [3H]mannose. The nonglycosylated low M(r) form of the enzyme was not secreted as shown by the decreasing activity in cell-free medium which paralleled the time-dependent secretion of the enzyme. Tunicamycin had no effect on BSDL synthesis. Nevertheless, the nonglycosylated BSDL was apparently not degraded in any cell compartment as shown in part by the enzyme activity accumulation within cells upon brefeldin A treatment. The BSDL expressed by AR 4-2 J cells was characterized by a Km of 68 +/- 30 microM and a kcat of 106 +/- 19 min-1. The sequestrated BSDL due to tunicamycin treatment of cells presents a significant increase of Km of over 10 times to 757 +/- 303 microM. kcat was affected by a factor of approximately 4-445 +/- 22 min-1. These data correlated with an approximately 2.5-fold decrease of the esterolytic activity following inhibition of the N-glycosylation of the protein. The nonglycosylated BSDL was less stable to temperature than the native form. Processing inhibitors (castanospermine, 1-deoxymannojirimycin, and swainsonine) had no effect either on the enzyme activity or on its secretion. Results suggested first that the transfer of the oligosaccharide precursor to the nascent BSDL is essential for the folding of the fully active BSDL. Second that the glycan structure is required for the enzyme secretion.

Characterization of the oligosaccharide moiety of VIP receptor from the human pancreatic cell line BxPC-3

The human pancreatic cell line BxPC-3 displays two classes of binding sites with high and low affinity for VIP. The order of potency of VIP-related peptides in inhibiting either [125I]VIP or [125I]N-AcPACAP27 binding and in stimulating cAMP production was typical of the human VIP receptor. By combining affinity labeling with glycosidase treatments, we have characterized the VIP receptor as a M(r) = 68,200 glycoprotein, consisting of a M(r) = 39,300 polypeptide core with at least three N-linked oligosaccharide chains. In addition, our results revealed the presence of a low amount of sialic acid residues in the carbohydrate moiety of receptor.

Variation of the glycosylation of human pancreatic bile-salt-dependent lipase

Glycoproteins of human pancreatic juice were characterized by means of lectins after electrophoresis and electrotransfer to nitrocellulose membranes. For the detected glycoproteins, only a 100-kDa glycoprotein varied in the pancreatic juice from a normal patient (i.e. without any pancreatic disorder) compared to the pancreatic juice from a patient suffering from chronic pancreatitis. This protein, which is the only protein in human pancreatic juice which is O-glycosylated and N-glycosylated, was identified as the bile-salt-dependent lipase. Among the glycosylated proteins present in human pancreatic juice, only the glycosylation of bile-salt-dependent lipase differs between individuals. The enzyme was isolated either from normal or pathological human pancreatic juices. The purified variants have an identical molecular mass and amino-acid composition. As suspected from lectin affinity studies, the oligosaccharide composition differs between the variants. The structure of the N-linked oligosaccharides of the variant from the pancreatic juice of a normal donor correlated with complete processing and maturation of a complex-type N-glycan. Alteration of the maturation process can be detected for a bile-salt-dependent-lipase variant from a patient suffering with chronic pancreatitis, since the carbohydrate composition is compatible with the predominance of hybrid or high-mannose-type structures. The amount of sugar involved in O-glycosylation associated with the peanut agglutinin reactivity suggests the presence of 12-14 minimal Gal beta 1-->3GalNac-->T/S O-glycan structures which are sialylated and fucosylated. The amount of sugar involved in the O-linked oligosaccharide structure appears to be unchanged in the variants isolated from the pathological pancreatic juice.

The structure of N-linked oligosaccharides of human pancreatic bile-salt-dependent lipase

This study describes the structure of the N-linked oligosaccharide chains of bile-salt-dependent lipase isolated from the pancreatic juice of a normal donor. After hydrazinolysis, neutral sugar chains were separated from acidic chains by paper electrophoresis and were fractionated using serial column chromatography with immobilized lectins and Bio-Gel P-4 filtration. Structural analysis was performed by means of sequential glycosidase digestion and revealed that the neutral sugar chains are mainly of the biantennary complex type. Fucose residues were identified for some trimannosyl core structures and were alpha(1-6) or alpha(1-2) linked to the innermost GlcNAc residue and a terminal Gal residue, respectively. Sialyl residues were also involved in the oligosaccharide structures. Most of these structures have no linear N-acetyllactosamine repeats. Evidence from several approaches suggests that the sugar chains of the human pancreatic bile-salt-dependent lipase possess a blood-group-related antigenic determinant.

Is bile salt-dependent lipase concentration in serum of any help in pancreatic cancer diagnosis?

The diagnostic value of bile salt-dependent lipase for pancreatic diseases was tested in sera of 187 patients. Of these patients, 76 suffered from pancreatic carcinoma, 43 from nonmalignant liver diseases (cirrhosis and chronic hepatitis), 18 from acute pancreatitis, and 20 from chronic pancreatitis. The remaining subjects were controls without pancreatic pathology. Bile salt-dependent lipase was determined by a sandwich enzyme-linked immunosorbent assay using polyclonal antibodies. Amylase and CA 19-9 antigen were also determined. In sera from control patients, the mean level of bile salt-dependent lipase was 1.5 micrograms/L. This level is quite similar to that of patients with benign liver diseases (1.1 micrograms/L) and with chronic pancreatitis (1.4 micrograms/L), but it was raised to 3.5 micrograms/L in patients with acute pancreatitis and decreased to 0.5 microgram/L in subjects with pancreatic adenocarcinoma. Thirty percent of control subjects and 73% of cancer patients had a bile salt-dependent lipase serum level below the cutoff value of 0.5 microgram/L. In acute pancreatitis, 11 of 16 subjects had levels above 1.5 micrograms/L. Amylase level largely increased in acute pancreatitis but was normal in all other groups. Concerning CA 19-9 antigen, 65% of control patients and > 80% of patients with nonmalignant pancreatic or liver diseases had normal levels. In sera from cancer patients, 80% presented with high levels. Accordingly, 36 of 38 patients with pancreatic cancer had either low serum levels of bile salt-dependent lipase (< 0.5 microgram/L) or high values of CA 19-9 antigen (> 37 U/ml; sensitivity 95%).(ABSTRACT TRUNCATED AT 250 WORDS)

Human fetoacinar pancreatic protein: an oncofetal glycoform of the normally secreted pancreatic bile-salt-dependent lipase

A fetoacinar pancreatic protein (FAP) associated with the ontogenesis, differentiation and oncogenic transformation of the human exocrine pancreas has been purified from pancreatic juices of patients suffering from pancreatitis or duodenal cancers invading the pancreas [Escribano and Imperial (1989) J. Biol. Chem. 264, 21865-21871]. This protein has striking similarities, i.e. M(r), amino acid composition and N-terminal sequence, to the bile-salt-dependent lipase (BSDL) of normal human pancreatic secretion. The aim of this study was to gain further insight into the nature of the two proteins. Reactivity with the mouse monoclonal antibody J28 (mAb J28), which characterizes FAP, and enzyme activity could not be dissociated during biochemical purification of BSDL. Furthermore, a polyclonal antiserum raised against purified human BSDL reacted completely with FAP in Western-blot analysis giving additional support to the idea of similar molecular structures for BSDL and FAP. However, by the same technique, mAb J28 reacted with a relatively restricted population of BSDL molecules. The classical BSDL preparation could be separated into molecules bearing the J28 epitope and those devoid of it by immunoaffinity on immobilized mAb J28. The two subpopulations had identical N-terminal sequences and some differences in their amino acid compositions. However, they had different carbohydrate compositions. J28-epitope-bearing molecules were active on BSDL substrates, although their specific activity was decreased. These results are consistent with the existence of two closely related polypeptide chains with different glycan counterparts. Therefore, if the name FAP is reserved for molecules bearing the J28 epitope, which is linked to a carbohydrate-dependent structure. FAP could represent an oncofetal-related variant of BSDL. Our result is the first demonstration of the existence of an oncofetal-type subpopulation of an otherwise normally secreted human pancreatic enzyme.

Pancreatic bile salt dependent lipase from cod (Gadus morhua): purification and properties

The enzymatic basis for cod digestive lipolysis has been investigated. Lipase activity was found in aqueous extracts from pyloric caeca as well as in pancreatic tissue surrounding the caeca and the bile duct. A bile salt-dependent lipase (BSDL) was purified from either defatted powder of cod pyloric caeca or aqueous pancreatic extracts by combined affinity chromatography on cholate-Sepharose and gel filtration on Sephacryl S-200 HR. By SDS-PAGE analysis the molecular weight of purified cod BSDL was estimated to 60 kDa. The enzyme was totally dependent on bile salts for hydrolysis of insoluble fatty acid esters. Antiserum raised against purified cod BSDL reacted specifically with selected mammalian pancreatic BSDLs by Western blot analysis. Results presented in this paper strongly suggest that the bile salt-dependent lipase is the only pancreatic enzyme involved in lipid digestion in cod. The enzyme has been characterized and compared to human pancreatic BSDL with respect to substrate specificity, temperature- and pH-dependence and inhibitors. Both soluble and insoluble fatty acid esters were hydrolysed and the enzyme was 1,3-specific in hydrolysis of triolein. The enzyme was inhibited by di-isopropyl fluorophosphate and phenyl boronic acid, but not significantly by phenyl methyl sulfonyl fluoride. The cod BSDL is probably homologous to mammalian pancreatic BSDLs.

N-Butyl-N-methyl-4-nitrophenyl carbamate as a specific active site titrator of bile-salt-dependent lipases

The effect of a series of synthetic carbamates on the human (milk or pancreatic) bile-salt-dependent lipase (cholesterol esterase) was examined. N-isopropyl-O-phenyl, N-methyl-O-phenyl, N-butyl-(4-nitrophenyl), N-phenyl-(4-nitrophenyl), N-butyl-N-methyl and N-pentyl-O-phenyl carbamates were inhibitors of the enzyme activity, while O-isopropyl-N-phenyl, O-methyl-N-phenyl, O-benzyl-N-isopropyl and O-cyclohexyl-N-phenyl carbamates were not even recognized by the enzyme. The N-alkyl chain length is essential for the enzyme inhibition and N-butyl-(4-nitrophenyl) or N-pentyl-O-phenyl carbamates are more potent inhibitors than N-methyl-O-phenyl or N-isopropyl carbamates. The inhibition by reactive carbamates fits the criteria for mechanism-based inhibition: the inhibition is first-order with time, shows saturation kinetics with increasing carbamate concentration and leads to an inactive stoichiometric enzyme-inhibitor complex; the enzyme activity can be protected by a competitive inhibitor. Evidence is shown that the enzymatic nucleophilic attack of carbamates is directed at the carbonyl carbon atom and not the nitrogen atom. The inhibition of bile-salt-dependent lipase does not occur consecutive to the formation of a reactive isocyanate derivative of carbamate but via a tetrahedral intermediate involving essential residues implicated in the enzyme catalytic site. This intermediate evolves by liberation of alcohol (or phenol) and formation of an inactive carbamyl enzyme. Among the carbamates tested, N-butyl-N-methyl-(4-nitrophenyl) carbamate specifically inhibits the bile-salt-dependent lipase; the release of 4-nitrophenol from this carbamate is directly proportional to the enzyme inhibition and it may be defined as a specific active-site titrator for bile-salt-dependent lipases.