Relationship of human pancreatic cholesterol esterase gene structure with lipid phenotypes

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.

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.

Transcriptional regulation of the human carboxyl ester lipase gene in THP-1 monocytes: an E-box required for activation binds upstream stimulatory factors 1 and 2

The bile salt-stimulated carboxyl ester lipase (CEL) is important for the digestion and absorption of dietary lipids, and is expressed at high levels by the exocrine pancreas and the lactating mammary gland. However, the presence of CEL in human plasma suggests that the role of CEL in lipid metabolism may stretch beyond its function in the intestinal lumen, and possibly include interactions with cholesterol and oxidized lipoproteins to modulate the progression of atherosclerosis. We have used the CEL-expressing human monocytic cell line THP-1 to investigate the transcriptional regulation of the human CEL in monocytes. Analyses of the promoter region revealed that an E-box located at -47/-52 is necessary for CEL expression. Point mutations in the E-box almost completely abolish the transcriptional activity. Electrophoretic mobility-shift assay analyses reveal that the E-box binds the upstream stimulatory factors 1 and 2, and the binding of an upstream stimulatory factor-containing complex in THP-1 cells also requires the presence of a putative nuclear receptor-binding site at -60/-66. Furthermore, we demonstrate that the E-box is also necessary for CEL expression in the pancreas and the mammary gland, although there are tissue-specific requirements for additional activating elements.

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.