Localization of the lipid receptors CD36 and CLA-1/SR-BI in the human gastrointestinal tract: towards the identification of receptors mediating the intestinal absorption of dietary lipids.
The scavenger receptors CLA-1/SR-BI and CD36 interact with native and modified lipoproteins and with some anionic phospholipids. In addition, CD36 binds/transports long-chain free fatty acids. Recent biochemical evidences indicates that the rabbit CLA-1/SR-BI receptor can be detected in enterocytes, and previous studies showed the presence of mRNA for both CLA-1/SR-BI and CD36 in some segments of the intestinal tract. These findings prompted us to study their respective localization and distribution from the human stomach to the colorectal segments, using immunohistochemical methods. Their expression in the colorectal carcinoma-derived cell line Caco-2 was analyzed by Northern blotting. In the human intestinal tract, CLA-1/SR-BI was found in the brush-border membrane of enterocytes from the duodenum to the rectum. However, CD36 was found only in the duodenal and jejunal epithelium, whereas enterocytes from other intestinal segments were not stained. In the duodenum and jejunum, CD36 co-localized with CLA-1/SR-BI in the apical membrane of enterocytes. The gastric epithelium was immunonegative for both glycoproteins. We also found that CLA-1/SR-BI mRNA was expressed in Caco-2 cells and that its expression levels increased concomitantly with their differentiation. In contrast, the CD36 transcript was not found in this colon cell line, in agreement with the absence of this protein in colon epithelium. The specific localization of CLA-1/SR-BI and CD36 along the human gastrointestinal tract and their ability to interact with a large variety of lipids strongly support a physiological role for them in absorption of dietary lipids.
Lobo
M V
MV
Departamento de Investigación, Hospital Ramón y Cajal, Madrid, Spain.
Huerta
L
L
Ruiz-Velasco
N
N
Teixeiro
E
E
de la Cueva
P
P
Celdrán
A
A
Martín-Hidalgo
A
A
Vega
M A
MA
Bragado
R
R
D000945:Antigens, Differentiation, T-Lymphocyte; D000951:Antigens, Neoplasm; D015152:Blotting, Northern; D018955:CD36 Antigens / Q000235:genetics / Q000378:metabolism*; D018938:Caco-2 Cells; D003106:Colon / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism; D004064:Digestive System / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005753:Gastric Mucosa / Q000378:metabolism; D006801:Humans; D007082:Ileum / Q000378:metabolism; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins; D009928:Organ Specificity; D012333:RNA, Messenger / Q000378:metabolism; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B
D000945:Antigens, Differentiation, T-Lymphocyte; D000951:Antigens, Neoplasm; D018955:CD36 Antigens; C063419:CTAGE1 protein, human; D004041:Dietary Fats; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B