Cobalamin release from intrinsic factor and transfer to transcobalamin II within the rat enterocyte

Ramasamy, Muthiah; Alpers, David H.; Tiruppathì, Chinnaswamy; Seetharam, Bellur

doi:10.1152/ajpgi.1989.257.5.g791

Cited by 18 publications

(16 citation statements)

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“…1A). The transport of free-presented Cbl in Caco-2 cells was to be expected as (i) this cell line has a fetal enterocyte phenotype and (ii) free Cbl is known to be transcytosed by immature suckling rat enterocytes [27]. In neonatal piglets, Trugo et al [28] characterized free Cbl uptake as low, much the same for all three intestinal segments, less dependent on pH and independent of Ca 2+ and Mg 2+ .…”

Section: Discussionmentioning

confidence: 99%

Transcytosis and coenzymatic conversion of [<sup>57</sup>Co]cobalamin bound to either endogenous transcobalamin II or exogenous intrinsic factor in Caco-2 cells

Pons

Guy

Lambert

et al. 2000

Cell Physiol Biochem

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We have examined the intracellular route, coenzyme conversion and transcytosis rate of [⁵⁷ Co]-labeled cobalamin (Cbl) in function of its presentation to the apical side of Caco-2 cells, either free or bound to intrinsic factor (IF). The free-presented Cbl was progressively bound to endogenous transcobalamin II (TCII) which may stem, in part, from a basolateral to apical passage. Its transcytosis was TCII-mediated as it was abolished when antibodies to TCII were added to the apical medium. The apparent permeability coefficient (P_app) was estimated at 20.8±3.6, 103.5±17.7, 0.9±0.3 × 10^–5 cm/h for TCII-Cbl, IF-Cbl and haptocorrin-Cbl, respectively. Chloroquine inhibited the transcytosis rate of both TCII and IF-bound Cbl in a dose-dependent manner. Approximately 80% of apical Cbl, bound to either exogenous IF or endogenous TCII, was transported to the basolateral side as intact cyano[⁵⁷Co]Cbl whereas the remainder was converted into Ado-Cbl and CH₃-Cbl within the cells, as shown by HPLC analyses of a 1,000-g pellet and a 12,000-g supernatant. Coenzymatic conversion was virtually abolished by chloroquine. In conclusion, we suggest that apically presented free Cbl is internalized via TCII-dependent transport. The apically internalized CN-Cbl, bound to either IF or TCII, is processed via an acidic vesicle and part of it is converted to coenzymes, whereas bulk of CN-Cbl is transcytosed intact.

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Section: Discussionmentioning

confidence: 99%

Transcytosis and coenzymatic conversion of [<sup>57</sup>Co]cobalamin bound to either endogenous transcobalamin II or exogenous intrinsic factor in Caco-2 cells

Pons

Guy

Lambert

et al. 2000

Cell Physiol Biochem

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“…Under normal physiological conditions, the dietary Cbl present on the lumenal side bound to gastric intrinsic factor is transcytosed via IFCR in both the intact intestine (11,19) and in Caco-2 cells (7,20,21) and other polarized epithelial cells (22)(23)(24)(25). During intrinsic factor-mediated apical to basolateral transcytosis of Cbl, intrinsic factor is degraded by leupeptin-sensitive protease and Cbl is bound to transcobalamin II prior to its exit on the basolateral side (23)(24)(25).…”

Section: Discussionmentioning

confidence: 99%

“…In Vivo Transport of TC II in Rat-Six male adult rats (150 g) were orally administered with 125 I-TCII-Cbl (1 ϫ 10 6 dpm of TC II, Cbl bound 1.5 pmol) using feeding tube as described earlier (11). Four and 8 h following the oral administration of the ligand, the rats were anesthetized, and blood was drawn from the portal vein between the intestine and the liver.…”

Section: Methodsmentioning

confidence: 99%

Bipolar Functional Expression of Transcobalamin II Receptor in Human Intestinal Epithelial Caco-2 Cells

Bose¹,

Seetharam

Dahms³

et al. 1997

Journal of Biological Chemistry

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The plasma transport of cobalamin (Cbl 1 ; vitamin B 12 ) to all tissues/cells occurs bound to a plasma transporter, transcobalamin II (TC II), by receptor-mediated endocytosis (1) via transcobalamin II receptor (TC II-R). Recent studies (2) have shown that TC II-R is expressed as a non-covalent homodimer of molecular mass of 124 kDa in all human (2), rat (3), and rabbit (4) tissue plasma membranes. The plasma membrane expression of TC II-R is important for the tissue/cellular uptake of Cbl, since its functional inactivation in vivo by its circulatory antiserum causes intracellular deficiency of Cbl, which in turn results in the development of Cbl deficiency of the animal as a whole (4). Although TC II-R is expressed in the plasma membrane of all cells, its polarity of expression in epithelial cells is not known. Recent immunoblot studies (3) have revealed that in the rat kidney, TC II-R protein is expressed in both the isolated apical and basolateral membranes with an enrichment in the basolateral membranes by about 8-fold. However, how TC II-Cbl internalized via the TC II-R from either the apical or basolateral surface is processed is not known. Recent TC II-[ 57 Co]Cbl uptake studies (4) using filter-grown polarized Caco-2 cells have shown that [ 57 Co]Cbl taken up from the basolateral side in these cells was utilized as Cbl coenzymes, suggesting that these cells derive Cbl essential for their use from the basolateral side.Despite these studies, the details of intracellular sorting of Cbl and TC II by a polarized epithelial cell are poorly understood. The present studies were undertaken to address the issues related to polarized expression and function of TC II-R in human intestinally derived Caco-2 cells, a well established cell model used extensively to study nutrient transport and general intestinal epithelial cell biology (5, 6).The results of this study show that TC II-R is asymmetrically expressed in the ratio of 1:7 and 1:6.8 in the apical and the basolateral membranes of human intestinal mucosa and intestinally derived Caco-2 cells, respectively. Furthermore, when TC II-Cbl is presented on the apical side of Caco-2 cells or to the intestinal lumen of rats, TC II is transcytosed across the epithelial cell by a non-lysosomal pathway. In addition, these studies also demonstrate that when presented on the basolateral side, TC II is processed via the lysosomal pathway, resulting in the degradation of TC II and the utilization of intracellularly released Cbl as coenzymes.

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“…77,79,80 Previously, B 12 was assumed to leave the cells in complex with transcobalamin. [81][82][83] However, a series of cellular export experiments actually showed that B 12 exit from cultured cells occurs by transmembrane transport of the vitamin in its 'free' (nonproteinbound) form via MRP1. 76 Indeed, transport of the vitamin in its free form is also implicit by the fact that the Schilling test for diag nosing deficient B 12 absorption uses the measurement of free radioactive B 12 in the urine (after radioactive B 12 has been orally administered and all circulating B 12 binding proteins have been saturated by injection of unlabeled B 12 ).…”

Section: Transport Of B 12 In the Cellmentioning

confidence: 99%

Vitamin B12 transport from food to the body's cells—a sophisticated, multistep pathway

Nielsen

Rasmussen

Andersen

et al. 2012

Nat Rev Gastroenterol Hepatol

314

329

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Vitamin B(12) (B(12); also known as cobalamin) is a cofactor in many metabolic processes; deficiency of this vitamin is associated with megaloblastic anaemia and various neurological disorders. In contrast to many prokaryotes, humans and other mammals are unable to synthesize B(12). Instead, a sophisticated pathway for specific uptake and transport of this molecule has evolved. Failure in the gastrointestinal part of this pathway is the most common cause of nondietary-induced B(12) deficiency disease. However, although less frequent, defects in cellular processing and further downstream steps in the transport pathway are also known culprits of functional B(12) deficiency. Biochemical and genetic approaches have identified novel proteins in the B(12) transport pathway--now known to involve more than 15 gene products--delineating a coherent pathway for B(12) trafficking from food to the body's cells. Some of these gene products are specifically dedicated to B(12) transport, whereas others embrace additional roles, which explains the heterogeneity in the clinical picture of the many genetic disorders causing B(12) deficiency. This Review describes basic and clinical features of this multistep pathway with emphasis on gastrointestinal transport of B(12) and its importance in clinical medicine.

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Cobalamin release from intrinsic factor and transfer to transcobalamin II within the rat enterocyte

Cited by 18 publications

References 0 publications

Transcytosis and coenzymatic conversion of [<sup>57</sup>Co]cobalamin bound to either endogenous transcobalamin II or exogenous intrinsic factor in Caco-2 cells

Transcytosis and coenzymatic conversion of [<sup>57</sup>Co]cobalamin bound to either endogenous transcobalamin II or exogenous intrinsic factor in Caco-2 cells

Bipolar Functional Expression of Transcobalamin II Receptor in Human Intestinal Epithelial Caco-2 Cells

Vitamin B12 transport from food to the body's cells—a sophisticated, multistep pathway

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