Molecular cloning and characterization of the mouse carboxyl ester lipase gene and evidence for expression in the lactating mammary gland

A new prognostic factor of breast cancer: High carboxyl ester lipase expression related to poor survival

OBJECTIVE

The enzyme carboxyl ester lipase (CEL), known as bile salt-dependent lipase (BSDL) or bile salt-stimulated lipase (BSSL), is mainly expressed in pancreatic acinar cells and lactating mammary glands. To investigate the link between CEL expression of breast cancer (BC) tissues and the survival of BC patients by analyzing The Cancer Genome Atlas Breast Carcinoma (TCGA-BRCA) level 3 data.

METHODS

The clinical information and RNA-sequencing (RNA-Seq) expression data were downloaded from TCGA. Patients were divided into a high CEL expression group and a low CEL expression group using the optimal cutoff value (5.611) identified from the ROC curve. Chi-square test and Fisher exact test were used to find the correlation between the expression of CEL and clinicopathologic features. To assess the diagnostic capability, the receiver operating characteristic (ROC) curve of CEL was drawn. The survival differences between high and low CEL expression groups were compared by Cox regression analysis. Log-rank test was applied to the calculation of p values and the comparison of the Kaplan-Meier curves. Furthermore, Gene Expression Omnibus (GEO) datasets were used for external data validation.

RESULTS

Analysis of 1104 cases of tumor data showed that CEL was over-expressed in breast cancer. There were relationships between high CEL expression and clinicopathologic features. The high CEL expression group had a lower survival. By analyzing the area under the ROC curve (AUC) of CEL, it was found to have a limited diagnostic capability. CEL expression may be an independent prognostic factor for breast cancer survival through the multivariate analysis. The validation in GEO datasets also showed that CEL expression was higher in breast tumor tissues than in normal breast tissues. High CEL expression was associated with the poor overall survival of breast cancer.

CONCLUSIONS

High CEL expression may be an independent prognostic factor for the poor survival of breast cancer.

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.

The role of the carboxyl ester lipase (CEL) gene in pancreatic disease

The enzyme carboxyl ester lipase (CEL), also known as bile salt-dependent or -stimulated lipase (BSDL, BSSL), hydrolyzes dietary fat, cholesteryl esters and fat-soluble vitamins in the duodenum. CEL is mainly expressed in pancreatic acinar cells and lactating mammary glands. The human CEL gene resides on chromosome 9q34.3 and contains a variable number of tandem repeats (VNTR) region that encodes a mucin-like protein tail. Although the number of normal repeats does not appear to significantly influence the risk for pancreatic disease, single-base pair deletions in the first VNTR repeat cause a syndrome of endocrine and exocrine dysfunction denoted MODY8. Hallmarks are low fecal elastase levels and pancreatic lipomatosis manifesting before the age of twenty, followed by development of diabetes and pancreatic cysts later in life. The mutant protein forms intracellular and extracellular aggregates, suggesting that MODY8 is a protein misfolding disease. Recently, a recombined allele between CEL and its pseudogene CELP was discovered. This allele (CEL-HYB) encodes a chimeric protein with impaired secretion increasing five-fold the risk for chronic pancreatitis. The CEL gene has proven to be exceptionally polymorphic due to copy number variants of the CEL-CELP locus and alterations involving the VNTR. Genome-wide association studies or deep sequencing cannot easily pick up this wealth of genetic variation. CEL is therefore an attractive candidate gene for further exploration of links to pancreatic disease.

Levels of palmitic acid ester of hydroxystearic acid (PAHSA) are reduced in the breast milk of obese mothers

To achieve optimal development of a newborn, breastfeeding is extensively recommended, but little is known about the role of non-nutritive bioactive milk components. We aimed to characterize the fatty acid esters of hydroxy fatty acids (FAHFAs), namely palmitic acid hydroxystearic acids (PAHSAs)-endogenous lipids with anti-inflammatory and anti-diabetic properties, in human breast milk. Breast milk samples from 30 lean (BMI=19-23) and 23 obese (BMI>30) women were collected 72h postpartum. Adipose tissue and milk samples were harvested from C57BL/6J mice. FAHFA lipid profiles were measured using reverse phase and chiral liquid chromatography-mass spectrometry method. PAHSA regioisomers as well as other FAHFAs were present in both human and murine milk. Unexpectedly, the levels of 5-PAHSA were higher relative to other regioisomers. The separation of both regioisomers and enantiomers of PAHSAs revealed that both R- and S-enantiomers were present in the biological samples, and that the majority of the 5-PAHSA signal is of R configuration. Total PAHSA levels were positively associated with weight gain during pregnancy, and 5-PAHSA as well as total PAHSA levels were significantly lower in the milk of the obese compared to the lean mothers. Our results document for the first time the presence of lipid mediators from the FAHFA family in breast milk, while giving an insight into the stereochemistry of PAHSAs. They also indicate the negative effect of obesity on 5-PAHSA levels. Future studies will be needed to explore the role and mechanism of action of FAHFAs in breast milk.

Bovine milk proteome in the first 9 days: protein interactions in maturation of the immune and digestive system of the newborn

In order to better understand the milk proteome and its changes from colostrum to mature milk, samples taken at seven time points in the first 9 days from 4 individual cows were analyzed using proteomic techniques. Both the similarity in changes from day 0 to day 9 in the quantitative milk proteome, and the differences in specific protein abundance, were observed among four cows. One third of the quantified proteins showed a significant decrease in concentration over the first 9 days after calving, especially in the immune proteins (as much as 40 fold). Three relative high abundant enzymes (XDH, LPL, and RNASE1) and cell division and proliferation protein (CREG1) may be involved in the maturation of the gastro-intestinal tract. In addition, high correlations between proteins involved in complement and blood coagulation cascades illustrates the complex nature of biological interrelationships between milk proteins. The linear decrease of protease inhibitors and proteins involved in innate and adaptive immune system implies a protective role for protease inhibitor against degradation. In conclusion, the results found in this study not only improve our understanding of the role of colostrum in both host defense and development of the newborn calf but also provides guidance for the improvement of infant formula through better understanding of the complex interactions between milk proteins.

Bile salt-stimulated lipase plays an unexpected role in arthritis development in rodents

OBJECTIVE

The present study aimed to explore the hypothesis that bile salt-stimulated lipase (BSSL), in addition to being a key enzyme in dietary fat digestion during early infancy, plays an important role in inflammation, notably arthritis.

METHODS

Collagen-induced arthritis (CIA) and pristane-induced arthritis (PIA) in rodents are commonly used experimental models that reproduce many of the pathogenic mechanisms of human rheumatoid arthritis, i.e. increased cellular infiltration, synovial hyperplasia, pannus formation, and erosion of cartilage and bone in the distal joints. We used the CIA model to compare the response in BSSL wild type (BSSL-WT) mice with BSSL-deficient 'knock-out' (BSSL-KO) and BSSL-heterozygous (BSSL-HET) littermates. We also investigated if intraperitoneal injection of BSSL-neutralizing antibodies affected the development or severity of CIA and PIA in mice and rats, respectively.

RESULTS

In two consecutive studies, we found that BSSL-KO male mice, in contrast to BSSL-WT littermates, were significantly protected from developing arthritis. We also found that BSSL-HET mice were less prone to develop disease compared to BSSL-WT mice, but not as resistant as BSSL-KO mice, suggesting a gene-dose effect. Moreover, we found that BSSL-neutralizing antibody injection reduced both the incidence and severity of CIA and PIA in rodents.

CONCLUSION

Our data strongly support BSSL as a key player in the inflammatory process, at least in rodents. It also suggests the possibility that BSSL-neutralizing agents could serve as a therapeutic model to reduce the inflammatory response in humans.

Comparative Structures and Evolution of Vertebrate Carboxyl Ester Lipase (CEL) Genes and Proteins with a Major Role in Reverse Cholesterol Transport

Bile-salt activated carboxylic ester lipase (CEL) is a major triglyceride, cholesterol ester and vitamin ester hydrolytic enzyme contained within pancreatic and lactating mammary gland secretions. Bioinformatic methods were used to predict the amino acid sequences, secondary and tertiary structures and gene locations for CEL genes, and encoded proteins using data from several vertebrate genome projects. A proline-rich and O-glycosylated 11-amino acid C-terminal repeat sequence (VNTR) previously reported for human and other higher primate CEL proteins was also observed for other eutherian mammalian CEL sequences examined. In contrast, opossum CEL contained a single C-terminal copy of this sequence whereas CEL proteins from platypus, chicken, lizard, frog and several fish species lacked the VNTR sequence. Vertebrate CEL genes contained 11 coding exons. Evidence is presented for tandem duplicated CEL genes for the zebrafish genome. Vertebrate CEL protein subunits shared 53-97% sequence identities; demonstrated sequence alignments and identities for key CEL amino acid residues; and conservation of predicted secondary and tertiary structures with those previously reported for human CEL. Phylogenetic analyses demonstrated the relationships and potential evolutionary origins of the vertebrate CEL family of genes which were related to a nematode carboxylesterase (CES) gene and five mammalian CES gene families.

Lipid digestion and absorption in early life: an update

PURPOSE OF REVIEW

To highlight our understanding of digestion and absorption of dietary lipids in newborn infants, and specifically how these processes differ from those in children and adults.

RECENT FINDINGS

The intestinal concentration of pancreatic triglyceride lipase (PTL) and bile salts is lower in newborns compared to later in life. Instead the PTL-related protein 2 and bile salt-stimulated lipase (BSSL) are the key enzymes secreted from pancreas, which in concerted action with gastric lipase operate to achieve efficient fat absorption during infancy. BSSL is also present in human milk which affects fat absorption and growth in breast-fed preterm infants. Under conditions of low luminal bile salt concentrations fat absorption is likely to occur from liquid crystalline product phases, which may result in absorption from an extended part of the small intestinal mucosal surfaces compared to adults. Chylomicron assembly and secretion also seem to adapt to the specific situation of the newborn.

SUMMARY

Both fat digestion and product absorption are different in newborn infants compared to adults; other lipases are used for digestion and different physical-chemical phases may be used for product absorption. Why these differences occur is still an unsolved question of considerable importance to neonatal nutrition.

Intestinal Monoacylglycerol Metabolism

Intestinal monoacylglycerol (MG) metabolism is well known to involve its anabolic reesterification to triacylglycerol (TG). We recently provided evidence for enterocyte MG hydrolysis and demonstrated expression of the monoacylglycerol lipase (MGL) gene in human intestinal Caco-2 cells and rodent small intestinal mucosa. Despite the large quantities of MG derived from dietary TG, the regulation of MG metabolism in the intestine has not been previously explored. In the present studies, we examined the mRNA expression, protein expression, and activities of the two known MG-metabolizing enzymes, MGL and MGAT2, in C57BL/6 mouse small intestine, as well as liver and adipose tissues, during development and under nutritional modifications. Results demonstrate that MG metabolism undergoes tissue-specific changes during development. Marked induction of small intestinal MGAT2 protein expression and activity were found during suckling. Moreover, while substantial levels of MGL protein and activity were detected in adult intestine, its regulation during ontogeny was complex, suggesting post-transcriptional regulation of expression. In addition, during the suckling period MG hydrolytic activity is likely to derive from carboxyl ester lipase rather than MGL. In contrast to intestinal MGL, liver MGL mRNA, protein and activity all increased 5-10-fold during development, suggesting that transcriptional regulation is the primary mechanism for hepatic MGL expression. Three weeks of high fat feeding (40% kcal) significantly induced MGL expression and activity in small intestine relative to low fat feeding (10% kcal), but little change was observed upon starvation, suggesting a role for MGL in dietary lipid assimilation following a high fat intake.

Bile salt-stimulated lipase and pancreatic lipase-related protein 2 are the dominating lipases in neonatal fat digestion in mice and rats

During infancy, the basic conditions for digestion of dietary fat differ from later in life. The bile salt-stimulated lipase (BSSL) is an enzyme expressed in the exocrine pancreas and in some species (including human) also in the lactating mammary gland and secreted with the milk. The aim of this study was to compare the ontogeny of four pancreatic lipases [BSSL, pancreatic triglyceride lipase (PL), pancreatic lipase-related protein 2 (PLRP2), and phospholipase A2 (PLA2)] in one species that supplies BSSL with milk (the mouse) and one that does not (the rat). We followed expression of the four pancreatic lipases from postnatal d 1 until after weaning in both species. We found that BSSL and PLRP2, two lipases with broad substrate specificity, dominated. It was not until weaning that significant expression of PL and PLA2 were induced. Thus, BSSL and PLRP2 seem to be responsible for fat digestion as long as milk is the main food. Moreover, the early temporal pattern of BSSL expression differed between species. We speculate that the milk-borne BSSL is able to compensate for a slower ontogeny of pancreatic BSSL expression in the mouse.

Association between a polymorphism in the carboxyl ester lipase gene and serum cholesterol profile

Carboxyl ester lipase (CEL) is involved in the hydrolysis and absorption of dietary lipids, but it is largely unknown to what extent CEL could be involved in determining the serum lipid levels. The C-terminal part of CEL consists of a unique structure with proline-rich O-glycosylated repeats of 11 amino-acid residues each. The common variant of the human CEL gene contains 16 proline-rich repeats, but there is a high degree of polymorphism in the repeated region. While the biological function of the polymorphic repeat region is unknown, it has been suggested that it may be important for protein stability and/or secretion of the enzyme. Given that the polymorphism in the repeated region may affect the functionality of the protein, this study aimed to investigate whether the number of repeated units is correlated to serum lipid phenotype. Comparison of CEL repeat genotype and serum lipid phenotype revealed an association between the number of repeats and serum cholesterol profile. Individuals carrying at least one allele with fewer than the common 16 repeats had significantly lower total and low-density lipoprotein (LDL) cholesterol levels compared to individuals carrying two common alleles. This gives support to the notion that CEL may be involved in determining the plasma lipid composition.

The Nuclear Factor I (NFI) gene family in mammary gland development and function

Mammary gland development and function require the coordinated spatial and temporal expression of a large fraction of the mammalian genome. A number of site-specific transcription factors are essential to achieve the appropriate growth, branching, expansion, and involution of the mammary gland throughout early postnatal development and the lactation cycle. One family of transcription factors proposed to play a major role in the mammary gland is encoded by the Nuclear Factor I (NFI) genes. The NFI gene family is found only in multicellular animals, with single genes being present in flies and worms and four genes in vertebrates. While the NFI family expanded and diversified prior to the evolution of the mammary gland, it is clear that several mammary-gland specific genes are regulated by NFI proteins. Here we address the structure and evolution of the NFI gene family and examine the role of the NFI transcription factors in the expression of mammary-gland specific proteins, including whey acidic protein and carboxyl ester lipase. We discuss current data showing that unique NFI proteins are expressed during lactation and involution and suggest that the NFI gene family likely has multiple important functions throughout mammary gland development.

Carboxyl ester lipase: structure-function relationship and physiological role in lipoprotein metabolism and atherosclerosis

Carboxyl ester lipase (CEL), previously named cholesterol esterase or bile salt-stimulated (or dependent) lipase, is a lipolytic enzyme capable of hydrolyzing cholesteryl esters, tri-, di-, and mono-acylglycerols, phospholipids, lysophospholipids, and ceramide. The active site catalytic triad of serine-histidine-aspartate is centrally located within the enzyme structure and is partially covered by a surface loop. The carboxyl terminus of the protein regulates enzymatic activity by forming hydrogen bonds with the surface loop to partially shield the active site. Bile salt binding to the loop domain frees the active site for accessibility by water-insoluble substrates. CEL is synthesized primarily in the pancreas and lactating mammary gland, but the enzyme is also expressed in liver, macrophages, and in the vessel wall. In the gastrointestinal tract, CEL serves as a compensatory protein to other lipolytic enzymes for complete digestion and absorption of lipid nutrients. Importantly, CEL also participates in chylomicron assembly and secretion, in a mechanism mediated through its ceramide hydrolytic activity. Cell culture studies suggest a role for CEL in lipoprotein metabolism and oxidized LDL-induced atherosclerosis. Thus, this enzyme, which has a wide substrate reactivity and diffuse anatomic distribution, may have multiple functions in lipid and lipoprotein metabolism, and atherosclerosis.

Human bile salt-stimulated lipase has a high frequency of size variation due to a hypervariable region in exon 11

The apparent molecular mass of human milk bile salt-stimulated lipase (BSSL) varies between mothers. The molecular basis for this is unknown, but indirect evidence has suggested the differences to reside in a region of repeats located in the C-terminal part of the protein. We here report that a polymorphism within exon 11 of the BSSL gene is the explanation for the molecular variants of BSSL found in milk. By Southern blot hybridization we analyzed the BSSL gene from mothers known to have BSSL of different molecular masses in their milk. A polymorphism was found within exon 11, previously shown to consist of 16 near identical repeats of 33 bp each. We detected deletions or, in one case, an insertion corresponding to the variation in molecular mass of the BSSL protein found in milk from the respective woman. Furthermore, we found that 56%, out of 295 individuals studied, carry deletions or insertions within exon 11 in one or both alleles of the BSSL gene. Hence, this is a hypervariable region and the current understanding that exon 11 in the human BSSL gene encodes 16 repeats is an oversimplification and needs to be revisited. Natural variation in the molecular mass of BSSL may have clinical implications.

The cloning and expression of a murine triacylglycerol hydrolase cDNA and the structure of its corresponding gene

A novel murine cDNA for triacylglycerol hydrolase (TGH), an enzyme that is involved in mobilization of triacylglycerol from storage pools in hepatocytes, has been cloned and expressed. The cDNA consists of 1962 bp with an open reading frame of 1695 bp that encodes a protein of 565 amino acids. Murine TGH is a member of the CES1A class of carboxylesterases and shows a significant degree of identity to other carboxylesterases from rat, monkey and human. Expression of the cDNA in McArdle RH7777 hepatoma cells showed a 3-fold increase in the hydrolysis of p-nitrophenyl laurate compared to vector-transfected cells. The highest expression of TGH was observed in the livers of mice, with lower expression in kidney, heart, adipose and intestinal (duodenum/jejunum) tissues. The murine gene that encodes TGH was cloned and exon-intron boundaries were determined. The gene spans approx. 35 kb and contains 14 exons. The results will permit future studies on the function of this gene via gene-targeting experiments and analysis of transcriptional regulation of the TGH gene.

Characterization of the gorilla carboxyl ester lipase locus, and the appearance of the carboxyl ester lipase pseudogene during primate evolution

In this study we report on the isolation and characterization of the gorilla carboxyl ester lipase gene, CEL, and the corresponding CEL pseudogene. We also report on the age of the CEL pseudogene. The gorilla CEL gene is 10.5kb long and comprises 11exons intervened by introns similar to the situation in man, mouse and rat. The encoded protein is 998amino acids long and includes a 23amino acid-long leader peptide. Comparison of the coding sequence, excluding exon 11, of CEL from gorilla and man reveals a 97% similarity. Exon 11, which encodes the characteristic proline rich repeats, contains 39 repeated units in gorilla compared to 16 in man. A truncated CEL pseudogene, with the same organization as that found in man, is also shown to be present in the gorilla genome. The gorilla CEL pseudogene is 4.9kb in length and consists of 5exons interrupted by introns. Southern analysis of the gorilla CEL locus shows that the locus is arranged in a similar way as in man with the functional CEL gene being the most 5' one. To bring further insight to the events involved in the rearrangement of the CEL locus, genomic Southern analyses were performed across several primates; Homo sapiens, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus and Macaca arctoides. Results presented show that the CEL gene duplication occurred prior to the separation of Hominidae (man, chimpanzee, gorilla and orangutan) from Old World monkeys (macaque). The deletion of the original CEL gene giving rise to the truncated version of the CEL gene seems, however, to be restricted to man and the great apes only.

Carboxyl ester lipase activity in milk prevents fat-derived intestinal injury in neonatal mice

Carboxyl ester lipase (bile salt-stimulated lipase) is a pancreatic enzyme capable of hydrolyzing esters of cholesterol and fat-soluble vitamins. It also efficiently digests triglycerides (TG) into free fatty acids and glycerol and is abundant in the milk of humans and several other species. We used the mouse as a model to test the hypothesis that milk-derived carboxyl ester lipase (CEL) digests milk TG and that without its activity milk lipids and their digestion intermediates can disrupt the intestinal epithelium of neonates. CEL protein and enzymatic activity were shown to be abundant in mouse milk. After 24-h administration of the CEL-specific inhibitor, WAY-121,751-5, the small intestines of treated and control neonates were analyzed histologically for signs of fat malabsorption and injury to their villus epithelium. In vehicle-fed controls, TG were digested and absorbed in the duodenum and jejunum, whereas, in inhibitor-fed littermates, large intracellular neutral lipid droplets accumulated in enterocytes of the ileum, resulting in damage to the villus epithelium. Similar results were observed in neonates nursed by CEL knockout females compared with heterozygous controls. The results suggest that lack of CEL activity causes incomplete digestion of milk fat and lipid accumulation by enterocytes in the ileum of neonatal mice.

Regulation of milk protein gene expression

Studies using both transgenic mice and transfected mammary epithelial cells have established that composite response elements containing multiple binding sites for several transcription factors mediate the hormonal and developmental regulation of milk protein gene expression. Activation of signal transduction pathways by lactogenic hormones and cell-substratum interactions activate transcription factors and change chromatin structure and milk protein gene expression. The casein promoters have binding sites for signal transducers and activators of transcription 5, Yin Yang 1, CCAAT/enhancer binding protein, and the glucocorticoid receptor. The whey protein gene promoters have binding sites for nuclear factor I, as well as the glucocorticoid receptor and the signal transducers and activators of transcription 5. The functional importance of some of these factors in mammary gland development and milk protein gene expression has been elucidated by studying mice in which some of these factors have been deleted.

Relationship of human pancreatic cholesterol esterase gene structure with lipid phenotypes

Pancreatic cholesterol esterase is one of the enzymes that plays a pivotal role in cholesterol absorption. Differences in the genotype of this enzyme could affect the susceptibility of individuals to dyslipidemia and/or cardiovascular disease. We undertook this study to investigate if any correlation exists between restriction fragment length polymorphism in the human pancreatic cholesterol esterase gene and serum lipid levels. DNA from 96 healthy adults was restricted with Stu I, Southern blotted, and probed with cDNA of human pancreatic cholesterol esterase. Results revealed six distinct patterns which were classified as A, B, C, D, E, and F which had a population frequency of 1%, 34.5%, 49%, 12.5%, 1% and 2% respectively. Correlation of the distribution of lipid and lipoprotein levels by pattern and sex revealed a significant interaction between pattern type and HDL (p=0.03) in the most common group (group C) for males. Male patients of pattern C tended to have a lower LDL cholesterol than non-pattern C males (p=0.07); in addition, 80% of all males in the study population with LDL cholesterol under 100 mg/dl were found in pattern C. Thus, the most common Stu I RFLP genotype is associated with a favorable lipid phenotype. This report shows an association between the human pancreatic cholesterol esterase genotype and serum lipid levels. Further analysis of a larger study group with Stu I and alternative polymorphic restriction enzymes is warranted, to confirm this biologically plausible result.

Studies of the regulation of the mouse carboxyl ester lipase gene in mammary gland

The lactating mammary gland and pancreas of mouse constitute the main tissues for synthesis and secretion of a bile-salt-stimulated lipase called carboxyl ester lipase (CEL). In this paper we have analysed the endogenous CEL gene expression in mammary gland. It is shown that the gene is expressed at day 14 of pregnancy, which is synchronous with that of the whey acidic protein (WAP) gene. Even though the CEL and WAP genes are induced at the same time during mammary gland differentiation, their regulation is different with respect to dependence on lactogenic hormones. The high induction of the WAP gene expression due to the activation of signal transducer and activator of transcription (STAT)5 by prolactin has not been observed for the CEL gene, even though it has been demonstrated that both STAT5 isoforms interact with one of the gamma-interferon activation sequence sites in the promoter of the CEL gene. Hence we have demonstrated that the prolactin/STAT5 signal is not involved in a general and significant activation of 'milk genes'. Instead of a direct effect of the lactogenic hormones, the up-regulation of the CEL gene is correlated with an increase in the number of differentiated epithelial cells. Furthermore, promoter studies using the mammary-gland-derived cell line, HC11, show that a major positive element in the CEL gene promoter interacts with a member(s) of the CCAAT-binding transcription factor/nuclear factor 1 family, binding to a palindromic site. Binding of this factor(s) is important for the tissue-specific activation of the CEL gene in the mammary gland, because no activation by this factor(s) was seen in cells of pancreatic origin.

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.

Modified low density lipoprotein enhances the secretion of bile salt-stimulated cholesterol esterase by human monocyte-macrophages. species-specific difference in macrophage cholesteryl ester hydrolase

Reverse transcriptase-polymerase chain reaction was used to study the biosynthesis of two different cholesteryl ester hydrolases by human and mouse macrophages. Oligonucleotide primers for bile salt-stimulated cholesterol esterase yielded positive reactions with RNA isolated from human peripheral blood monocytes, monocyte-derived macrophages, the human monocytic THP-1 cells, and phorbol ester-induced THP-1 macrophages. In contrast, oligonucleotide primers for hormone-sensitive lipase yielded positive reactions only with RNA isolated from non-differentiated human THP-1 monocytic cells and peripheral blood monocytes, but not those obtained from differentiated THP-1 macrophages or monocyte-derived macrophages. Thus, while human monocytes were capable of synthesizing both enzymes, human macrophages synthesized only bile salt-stimulated cholesterol esterase and not the hormone-sensitive lipase. The synthesis of bile salt-stimulated cholesterol esterase by human macrophages was confirmed by detection of bile salt-stimulated cholesteryl ester hydrolytic activity in conditioned media of differentiated THP-1 cells and human peripheral blood monocyte-derived macrophages. Moreover, incubating human macrophages with oxidized low density lipoprotein (LDL) or acetylated LDL increased bile salt-stimulated cholesterol esterase activity in the conditioned media of these cells. These results with human macrophages were contrasted with results of studies with mouse macrophages, which showed the presence of hormone-sensitive lipase mRNA but not the bile salt-stimulated cholesterol esterase mRNA. Taken together, these results demonstrated species-specific differences in expression of cholesteryl ester hydrolytic enzymes in macrophages. The expression of bile salt-stimulated cholesterol esterase by human macrophages, in a process inducible by modified LDL, suggests a role of this protein in atherogenesis.

Naturally occurring variants of human milk bile salt-stimulated lipase

Analysis of milk samples from a number of lactating women revealed molecular variants of bile salt-stimulated lipase (BSSL) of both lower and higher molecular mass than that commonly occurring. In contrast to previous observations, we report on individuals having only a variant of lower mass, both one of lower and one of common mass, or both one of lower and one of higher mass of the lipase. From two individuals we purified the lower molecular mass BSSL variant and characterized it. The amount of lipase in the milk of these two individuals was considerably less than average (mean of 10 women with BSSL of the most common molecular mass). The BSSL variant of lower mass showed the same bile salt activation, pH dependency, temperature stability as those most commonly occurring. We could localize the difference in mass to the large O-glycosylated repeat sequence close to the C-terminus of the protein. With respect to all characteristics studied, the BSSL variant of higher mass was also similar to that most commonly ocurring. Again, the difference in mass could be localized to the repeat region of the protein. Hence, it appears as if the repeat region, normally carrying 16 repeats of 11 amino acids each, varies in size between individuals.

Recombinant human bile salt-stimulated lipase: an example of defective O-glycosylation of a protein produced in milk of transgenic mice

The expression of recombinant human bile salt-stimulated lipase (bssl) was targeted to the lactating mammary gland of transgenic mice. Expression of recombinant genes comprising bsslcDNA, or alternatively genomic bssl DNA, under control of regulatory elements derived from the murine whey acidic protein (wap) gene was achieved and evaluated. Constructs containing genomic bssl sequences mediated high levels (0.5-1 mg ml-1) of recombinant human BSSL in the milk. The recombinant BSSL produced was purified, biochemically characterized and compared to native BSSL and recombinant BSSL produced in mouse C127 and hamster CHO cells. Recombinant BSSL derived from transgenic mice showed a different migration and distribution after SDS-PAGE electrophoresis, lower apparent molecular mass on size-exclusion chromatography and no detectable interactions with a panel of lectins. These results indicate a significantly lower degree of O-glycosylation of recombinant BSSL in milk from transgenic mice than was found for the native enzyme or recombinant CHO- or C127 cell-produced BSSL. Despite these differences, mouse-milk-derived recombinant BSSL exhibited similar lipase activity, the same stability to low pH and similar sensitivity to elevated temperatures as the native enzyme. The observation that mouse-C127-cell-produced recombinant BSSL is heavily O-glycosylated makes species-related restrictions less attractive as an explanation for the reduced O-glycosylation.