PMID:6321516

Citation	Levine, JS, Allen, RH, Alpers, DH and Seetharam, B (1984) Immunocytochemical localization of the intrinsic factor-cobalamin receptor in dog-ileum: distribution of intracellular receptor during cell maturation. J. Cell Biol. 98:1111-8
Abstract	Absorption of cobalamin is facilitated by the binding of the intrinsic factor-cobalamin complex (IF-cbl) to specific receptors in the ileum. The physical and biochemical characteristics of this ligand-receptor binding reaction have been extensively studied, but little is known about the cellular mechanisms or receptor synthesis, intracellular transport, and expression on the microvillus surface membrane. We attempted to delineate these mechanisms by using ultrastructural immunocytochemistry to localize the IF-cbl receptor in the crypt, mid-villus, and villus tip regions of mucosal biopsies obtained from the ileum of anesthetized dogs. Prior to initiating the ileal localization studies, the antisera to purified canine IF-cbl receptor that was employed in our studies was shown to have specificity for site (e.g., ileal enterocytes vs. other cells within the gastrointestinal tract) and immunohistochemical specificity. Receptor synthesis in endoplasmic reticulum begins in crypt enterocytes, but continues in cells throughout the villus. In the mid-villus region synthesized receptor translocates vectorially to the microvillus surface associated with membranous vesicles and then inserts into the microvillus pit. Receptor remains fixed to the microvillus pit and does not distribute uniformly over the brush border membrane. All villus tip enterocytes contained IF-cbl receptor in microvillus pits, vesicles, and endoplasmic reticulum, but in addition extensive perinuclear membrane staining was evident as well as re-internalized receptor associated with multivesicular bodies. Basolateral membranes contained no receptor at any level of the villus. These observations suggest that the IF-cbl receptor (a) translocates to the apical cell surface at the mid-villus region by transport in vesicles, (b) directly inserts into and then remains fixed in microvillus pits, (c) is elaborated on the luminal surface most extensively in villus tip cells, and (d) although reinternalized, does not move IF and/or cbl to the basolateral cell surface.
Links	PubMed PMC2113133
Keywords	Animals; Cell Compartmentation; Cell Differentiation; Dogs; Ileum/metabolism; Intestinal Mucosa/metabolism; Microscopy, Electron; Microvilli/metabolism; Receptors, Cell Surface/immunology; Receptors, Cell Surface/metabolism; Vitamin B 12/metabolism
edit table

Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
CANLF:CUBN		GO:0016324: apical plasma membrane	ECO:0000314:		C		Figure 7 shows that an antibody for the intrinsic factor-cobalamin complex (IF-cbl) [now known and cubam or cubilin and amnionless] is found at the microvillus pits of the apical membrane of ileum cells.	complete CACAO 9853
CANLF:CUBN	part_of	GO:0016324: apical plasma membrane	ECO:0000314: direct assay evidence used in manual assertion		C		Seeded From UniProt	complete

References

See Help:References for how to manage references in GONUTS.