Novel aspects of carboxyl ester lipase (CEL). Investigations on transcriptional regulation and tissue expression

Abstract

Carboxyl ester lipase (CEL) is a digestive enzyme that breaks down dietary fats in the duodenum, and it is mainly expressed by the pancreas and lactating mammary glands. A pathogenic variant of the CEL gene, named CEL-HYB1, is established as a risk factor for chronic pancreatitis and increases the disease risk by 5-fold in the European population. Interestingly, new data from our research group suggest that CEL-HYB1 is a risk factor for chronic pancreatitis that predominantly affect women. Furthermore, there are indications that the T-allele of a SNP present in the CEL promoter (rs541856133) is associated with CEL-HYB1. The same SNP variant may also increase the risk for developing diabetes.

This thesis aimed to understand the effect of the promoter SNP rs541856133 (C>T) on CEL gene expression, and to investigate whether CEL could be regulated by female sex hormones. Moreover, we wanted to explore the role of CEL outside of the digestive system, particularly in the pituitary gland.

By cellular models and a dual-reporter luciferase assay, we found that the CEL MUT promoter (rs541856133 (T)) exhibited increased activity compared to the CEL WT promoter (rs541856133 (C)) in HEK293 cells, but not in ZR-75-1 or HeLa cells. In silico analysis of the CEL promoter identified the zinc finger protein ZNF331 as a potential repressor predicted to bind to the SNP site, and with reduced binding affinity towards the CEL MUT promoter. However, ZNF331 was found to repress the activity of both promoter variants in HEK293 cells, with no effect observed in ZR-75-1 cells.

The in silico analysis also revealed putative estrogen receptor (ER) binding sites within the CEL promoter. In ZR-75-1 cells, ERα overexpression led to repression of the CEL promoter activity, while treatment with the ER modulator Tamoxifen not only reversed this effect but also enhanced the promoter activity. These findings may suggest a regulatory role for estrogen on CEL gene expression. Immunohistochemical analysis further confirmed the expression of the CEL protein in the human pituitary gland and that it co-localizes with the thyroid-stimulating hormone (TSH), possibly linking CEL to hormonal pathways.

Based on varying results in HEK293, ZR-75-1 and HeLa cells, we cannot conclude whether the CEL promoter SNP rs541856133 (T) significantly impacts CEL expression or if it is simply a tag associated with CEL-HYB1 without affecting gene expression Furthermore, our findings support a regulatory role for estrogen on CEL expression and highlights the enzyme’s potential involvement in endocrine functions through its presence in the pituitary gland.