Human milk bile-salt stimulated lipase. Sequence similarity with rat lysophospholipase and homology with the active site region of cholinesterases

Pancreatic adenocarcinoma, chronic pancreatitis, and MODY-8 diabetes: is bile salt-dependent lipase (or carboxyl ester lipase) at the crossroads of pancreatic pathologies?

Pancreatic adenocarcinomas and diabetes mellitus are responsible for the deaths of around two million people each year worldwide. Patients with chronic pancreatitis do not die directly of this disease, except where the pathology is hereditary. Much current literature supports the involvement of bile salt-dependent lipase (BSDL), also known as carboxyl ester lipase (CEL), in the pathophysiology of these pancreatic diseases. The purpose of this review is to shed light on connections between chronic pancreatitis, diabetes, and pancreatic adenocarcinomas by gaining an insight into BSDL and its variants. This enzyme is normally secreted by the exocrine pancreas, and is diverted within the intestinal lumen to participate in the hydrolysis of dietary lipids. However, BSDL is also expressed by other cells and tissues, where it participates in lipid homeostasis. Variants of BSDL resulting from germline and/or somatic mutations (nucleotide insertion/deletion or nonallelic homologous recombination) are expressed in the pancreas of patients with pancreatic pathologies such as chronic pancreatitis, MODY-8, and pancreatic adenocarcinomas. We discuss the possible link between the expression of BSDL variants and these dramatic pancreatic pathologies, putting forward the suggestion that BSDL and its variants are implicated in the cell lipid metabolism/reprogramming that leads to the dyslipidemia observed in chronic pancreatitis, MODY-8, and pancreatic adenocarcinomas. We also propose potential strategies for translation to therapeutic applications.

Isolation and Characterization of Purified Bile Salt Stimulated Human Milk Lipase

A method has been developed for the isolation and purification of bile-salt-stimulated human milk lipase. This method yields up to six times more enzyme than other reported methods and the specific activity is compara ble. The concentration of BSSL recovered from the whole milk was 0.65 percent of the original protein content. The molecular weight of the isolated protein was 120 kDa. During the course of the purification, both protein content and specific activity were monitored and the esterase and lipase activities of the isolated product were characterized in the presence of sodium taurocholate. Five separate isolations were carried out with the introduction of minor varia tions in the procedure, but the catalytic properties of the product remain unchanged.

Localization of carboxyl ester lipase in human pituitary gland and pituitary adenomas

Carboxyl ester lipase (CEL) is an enzyme that hydrolyzes a wide variety of lipid substrates, including ceramides, which are known to show inhibitory regulation of pituitary hormone secretion in experimental models. Because no studies on CEL expression in human pituitary and pituitary adenomas have been reported in the literature, we investigated CEL expression in 10 normal pituitary glands and 86 well-characterized pituitary adenomas [12 FSH/LH cell, 17 α-subunit/null cell, 6 TSH cell, 21 ACTH cell, 11 prolactin (PRL) cell, and 19 GH cell adenomas] using IHC, immunoelectron microscopy, Western blotting, and quantitative RT-PCR. In normal adenohypophysis, CEL was localized in GH, ACTH, and TSH cells. In adenomas, it was mainly found in functioning GH, ACTH, and TSH tumors, whereas its expression was poor in the corresponding silent adenomas and was lacking in FSH/LH cell, null cell, and PRL cell adenomas. Ultrastructurally, CEL was localized in secretory granules close to their membranes. This is the first study demonstrating CEL expression in normal human pituitary glands and in functioning GH, ACTH, and TSH adenomas. Considering that CEL hydrolyzes ceramides, inactivating their inhibitory function on pituitary hormone secretion, our findings suggest a possible role of CEL in the regulation of hormone secretion in both normal and adenomatous pituitary cells.

The monoclonal anti-BCL10 antibody (clone 331.1) is a sensitive and specific marker of pancreatic acinar cell carcinoma and pancreatic metaplasia

Acinar cell carcinoma (ACC) is a rare pancreatic cancer which may be difficult to distinguish from other solid nonadenocarcinoma tumors. The diagnosis depends on the demonstration of acinar differentiation, obtained with antibodies recognizing various pancreatic enzymes that, although specific, show different sensitivity. The C-terminal portion of the BCL10 protein shows homology with carboxyl ester hydrolase (CEH), an enzyme produced by pancreatic acinar cells. We investigated the usefulness of a C-terminal BCL10 monoclonal antibody in the diagnosis of ACCs. We examined normal pancreases and different pancreatic tumors including ACCs, mixed acinar-endocrine carcinomas, ductal adenocarcinomas, mucinous, serous, solid pseudopapillary, and endocrine neoplasms. In addition, various normal tissues and cases of pancreatic metaplasia of the gastroesophageal mucosa, cases of ectopic pancreas, gastrointestinal endocrine tumors, salivary and breast acinic cell carcinomas, gastric adenocarcinomas with and without acinar differentiation, and hepatocellular carcinomas were studied. BCL10 immunoreactivity paralleled that of CEH and was restricted to acinar cells of normal and ectopic pancreas, of pancreatic metaplasia, and of ACCs. The anti-BCL10 antibody was more sensitive in detecting ACCs and pancreatic metaplasia than antibodies directed against other pancreatic enzymes. We suggest using BCL10 antibody for diagnosing pancreatic tumors and whenever an acinar differentiation is suspected in gastrointestinal neoplastic and metaplastic lesions.

Incidence of molecular forms of bile salt-stimulated lipase in preterm and term human milk

Preterm and term human milk samples obtained at various times after delivery were analyzed for the presence of molecular forms of the human milk enzyme, bile salt-stimulated lipase (BSSL). Thirty-five percent of both the preterm and term milk samples contained two molecular forms of BSSL, of variable molecular mass. The remainder contained only one molecular species of either 115 kD (50%) or 120 kD (15%). The number of molecular forms present was not related to length of lactation, maternal age, gestation, or maternal blood group. The specific activity of BSSL purified from term milk was similar to that purified from preterm milk, and there was no difference in specific activity whether one or two molecular forms were present. This study demonstrates heterogeneity of both molecular mass and molecular forms. We conclude that preterm babies fed their own mother's milk are unlikely to be disadvantaged with respect to fat digestion as BSSL secreted in preterm milk appears to be very similar to that produced in term milk, although we cannot exclude other functional differences.

Structural organisation of human bile-salt-activated lipase probed by limited proteolysis and expression of a recombinant truncated variant

Bile-salt-activated lipase belongs to the cholinesterase alpha/beta-hydrolase-fold family of proteins. Here, we have investigated the structural organisation of the human isoform by mapping tryptic cleavage sites using limited proteolysis and by expression studies using a recombinant truncated variant. Two accessible regions in the tertiary structure were identified. The first is defined by a tryptic cleavage at Lys429 and lies within the alpha/beta-hydrolase fold in bile-salt-activated lipase between a central beta-sheet and an active-site histidine residue, as deduced from sequence similarity across the cholinesterases and known structural properties. This region exhibits a proteolytic and topological similarity to the lid region in pancreatic lipase. The other accessible region in the tertiary structure is defined by a tryptic cleavage at Arg520 and occurs within a catalytically non-essential segment Leu519-Gln535, as identified by expression of a truncated variant which lacks the C-terminus starting from Leu519. This region is consistent with an interdomain region between the cholinesterase-related part of the protein structure and the unique proline-rich C-terminal repeats. Both protease-sensitive regions appear to occur at domain borders, and, therefore, are consistent with a multi-domain structure. The truncated variant was fully functional as a lipase and as a bile-salt-stimulated esterase. However, compared to the full-length enzyme, the truncated variant showed an increased susceptibility to limited proteolysis, suggesting that the C-terminal repeats may regulate proteolytic degradation of the protein.

Recombinant human-milk bile-salt-stimulated lipase. Functional properties are retained in the absence of glycosylation and the unique proline-rich repeats

Human milk bile-salt-stimulated lipase ensures efficient utilization of milk lipid in breast-fed infants. The N-terminal two-thirds of the peptide chain is highly conserved and shows striking similarities to typical esterases. In contrast, the remaining C-terminal part consists of a unique sequence of 16 proline-rich O-glycosylated repeats of 11 residues each. Recently we could show, using recombinant lipase variants, that neither these repeats nor the single N-linked sugar chain are essential for catalytic efficiency. In the present study, we report on the lack of importance of glycosylation and the unique repeats for other important functional properties, i.e. bile-salt activation, heparin binding, heat stability, stability at low pH and resistance to proteolytic inactivation. Compared to native enzyme, recombinant full-length lipase produced in two mammalian cell lines differed slightly in glycosylation pattern with no effects on the functional properties. Moreover, a variant lacking all repeats and the C-terminal tail following the last repeat exhibited the same functional characteristics as purified native milk enzyme. Thus, the structural basis for all the typical and functionally important properties reside in the N-terminal conserved part, in spite of the fact that none of these properties are shared by typical esterases. We could however, demonstrate that the C-terminal repeats are responsible for the unusual behaviour of the enzyme in size-exclusion chromatography, resulting in a considerably higher than expected apparent molecular mass.

Cholinesterases and peanut agglutinin binding related to cell proliferation and axonal growth in embryonic chick limbs

Embryonic cholinesterases are assigned important functions during morphogenesis. Here we describe the expression of butyrylcholinesterase and acetylcholinesterase, and the binding of peanut agglutinin, and relate the results to mitotic activity in chick wing and leg buds from embryonic day 4 to embryonic day 9. During early stages, butyrylcholinesterase is elevated in cells under the apical ectodermal ridge and around invading motoraxons, while acetylcholinesterase is found in the chondrogenic core, on motoraxons and along the ectoderm. Peanut agglutinin binds to the apical ectodermal ridge and most prominently to the chondrogenic core. Measurements of thymidine incorporation and enzyme activities were consistent with our histological findings. Butyrylcholinesterase is concentrated near proliferative zones and periods, while acetylcholinesterase is associated with low proliferative activity. At late stages of limb development, acetylcholinesterase is concentrated in muscles and nonexistent within bones, while butyrylcholinesterase shows an inverse pattern. Thus, as in other systems, in limb formation butyrylcholinesterase is a transmitotic marker preceding differentiation, acetylcholinesterase is found on navigating axons, while peanut agglutinin appears in non-invaded regions. These data suggest roles for cholinesterases as positive regulators and peanut-agglutinin-binding proteins as negative regulators of neural differentiation.

Is there a specific lysophospholipase in human pancreatic juice?

The existence of a specific lysophospholipase in human pancreatic juice was evaluated. The proteins were separated by a series of chromatographic steps including Sephacryl S-200, cholate-Sepharose 4B, Sephadex G-100 and CM-Sephadex G-50. The enzyme activities against 1-palmitoyl lysolecithin (LL) as well as tributyrin (TB) and p-nitrophenyl butyrate (PNPB) were determined in all the fractions of these purification procedures. Enzyme activity against LL was always eluted in parallel with activities against TB and PNPB, and no unique activity against LL could be found. The specific activity against LL was 40-times lower than that against PNPB and 200-times lower than that against TB. It is concluded that there is no unique lysophospholipase in human pancreatic juice and that the hydrolysis of lysolecithin is most likely performed by carboxyl ester lipase.

Isolation and characterization of three lysophospholipases from the murine macrophage cell line WEHI 265.1

Anion exchange chromatography of WEHI 265.1 cell homogenates resolved the lysophospholipase activity into three peaks, when assayed using lysophosphatidylcholine as a substrate. Peaks 1 and 2 were purified by sequential hydrophobic interaction and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified peaks 1 and 2 indicated homogeneous proteins with apparent masses of 28 and 27 kDa, respectively. Peak 3 lysophospholipases was partially purified by hydrophobic, hydroxyapatite and gel filtration chromatography. Peak 3 lysophospholipase also had calcium-dependent phospholipase A2 activity, which further co-purified with the lysophospholipase activity. The three lysophospholipases were characterized with respect to substrate specificity, additional enzymatic activities and the effects of lipids, metal ions and other compounds on enzymatic activity. Peaks 1, 2 and 3 hydrolyzed lysophosphatidylcholine most readily, but lysophosphatidylethanolamine also served as substrate for each enzyme. Furthermore, all three enzymes hydrolyzed platelet activating factor and acetylated lysophosphatidylcholine. Each lysophospholipase was inhibited by free fatty acids and by palmitoyl carnitine, although the relative sensitivities to these agents differed among the enzymes. The lysophospholipase activities of peaks 1 and 2, but not peak 3, were inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate and N-ethylmaleimide. Although they had similar masses, the amino acid compositions of peaks 1 and 2 differed, indicating that these are distinct proteins rather than posttranslational modifications of the same gene product.

Two forms of human milk bile-salt-stimulated lipase

This study provides the first direct evidence for the existence of two active forms of the human milk enzyme bile-salt-stimulated lipase. Heparin-based affinity chromatography and size-exclusion chromatography were used to obtain two active forms of this enzyme with molecular masses of 97 and 120 kDa.