Lectin-like Ox-LDL Receptor Is Expressed in Human INT-407 Intestinal Cells: Involvement in the Transcytosis of Pancreatic Bile Salt–dependent Lipase

Abstract

We have recently shown that the pancreatic bile salt-dependent lipase (BSDL) can be taken up by intestinal cells and transported to the blood circulation. This mechanism likely involves (specific) receptor(s) able to bind BSDL and located at the apical intestinal cell membrane. In this study, using Int407 human intestinal cells cultured to form a tight epithelium, we attempted to characterize (the) BSDL receptor(s). We found that an apical 50-kDa protein was able to bind BSDL. Further, we have demonstrated that Int407 cells expressed the lectin-like oxidized-LDL receptor (LOX-1), the upregulation of which by oxidized-LDL potentiates the transcytosis of BSDL, whereas carrageenan and to a lesser extent polyinosinic acid and fucoidan decrease the enzyme transcytosis. The mAb JTX92, which blocks the LOX-1 receptor function, also impaired the BSDL transcytosis. To confirm these results, the cDNA encoding the human intestinal receptor LOX-1 has been cloned, inserted into vectors, and transfected into Int407 cells. Overexpression of LOX-1 by these cells leads to a substantial increase in the BSDL transcytosis. Globally, these data support the view that LOX-1 could be an intestinal receptor for BSDL, which is implicated in the transcytosis of this enzyme throughout Int407 cells. INTRODUCTIONThe bile salt-dependent lipase (BSDL, EC 3.1.1.13), also referred to as carboxyl ester lipase or bile salt-stimulated lipase, is a lipolytic enzyme, synthesized and secreted by the exocrine pancreas (Lombardo, 2001). The secretion of this digestive enzyme requires the participation of the Grp94 molecular chaperone (Bruneau and Lombardo, 1995;Bruneau et al., 1998). Once in the lumen of the duodenum, BSDL, in concert with other pancreatic lipolytic enzymes and preduodenal lipase, acts to complete the digestion of dietary lipids. Indeed, upon activation by primary bile salts, BSDL catalyzes the duodenal hydrolysis of cholesterol esters into free cholesterol and fatty acids before their absorption by intestinal cells (Howles et al., 1996;Weng et al., 1999). Although controversial (Howles et al., 1996), BSDL could also participate in the intestinal free cholesterol absorption (LopezCandales et al., 1993), acting as a cholesterol transfer protein (Myers-Payne et al., 1995), or as a cholesterol reesterifying enzyme after cholesterol absorption by intestinal cells (Bhat and Brockman, 1982).A fraction of BSDL, possibly associated with Grp94, reaches the vicinity of microvilli and upon binding to the surface of intestinal cells is internalized and transported up to the blood compartment (Bruneau et al., , 2000a(Bruneau et al., , 2000b(Bruneau et al., , 2003. Consequently, BSDL has been reported in the plasma of normolipidemic patients where it associates with apolipoprotein B-containing lipoproteins such as low-density lipoprotein (LDL), chylomicron and very-low-density lipoprotein (VLDL; Bruneau et al., 2003).The pathway of BSDL throughout intestinal cells has been recently delineated using Int407 cells (Bruneau et al., 2001), which do not e...

Internalization and Transcytosis of Pancreatic Enzymes by the Intestinal Mucosa

“…This heterogeneity may also be responsible for fluctuations in our quantitative results particularly evident for lipase over the endosomal compartment ( Figure 9B). Previous studies on BSDL have identified a receptor, LOX-1, located at the enterocyte luminal membrane responsible for its internalization (Bruneau et al 2003b). This finding entails internalization of BSDL as a rather specific event, and some cells may be more prone than others.…”

Bile salt–dependent lipase interacts with platelet CXCR4 and modulates thrombus formation in mice and humans

“…Once activated, BSDL, in concert with other digestive lipolytic enzymes, degrades dietary lipids and participates in the hydrolysis of cholesterol esters into free cholesterol and fatty acids (6). In the duodenum, a fraction of BSDL is internalized by enterocytes via the lectin-like oxidized LDL receptor (LOX-1) and transported to the blood compartment (7,8), where it partly associates with apolipoprotein B-containing lipoproteins in plasma (6). The concentration of circulating BSDL in human serum, determined by ELISA using polyclonal antibodies, is 1.5 ± 0.5 μg/l (9-11) but is elevated to a level as high as 7 μg/l in some pathological conditions, such as acute pancreatitis (12).…”

“…Although there are conflicting reports, the enzyme may be synthesized by macrophages and endothelial cells (14,15). Alternatively, BSDL, which has a heparin-binding site (16) and a V3-like loop domain (17), associates with intestinal cell-surface proteoglycans (7,8). In vitro studies have shown that BSDL induces vascular smooth muscle cell proliferation and evokes endothelial cell proliferation and chemotactic migration (13,18).…”

The role of lectin-like oxidised low-density lipoprotein receptor-1 in vascular pathology

“…LOX-1 is expressed on the main cells involved in atherogenesis as well as on the plaques themselves. 56 Although LOX-1 is located on a number of non-vascular cells such as chondrocytes and intestinal cells, 15,57 it is not as widely expressed as other scavenger receptors such as Cluster of Differentiation 36 (CD36). It is therefore an attractive target for the development of selective drug delivery systems.…”