title: Monocarboxylate transporter 1 is up-regulated in Caco-2 cells by the methionine precursor DL-2-hydroxy-(4-methylthio)butanoic acid.
abstract: The methionine precursor, DL-2-hydroxy-(4-methylthio)butanoic acid (HMTBA), is a synthetic source of dietary methionine, which is widely used as a poultry nutritional supplement. In the intestinal epithelium, HMTBA transport across the apical membrane is mediated by monocarboxylate transporter 1 (MCT1). The first step in biological utilisation of this methionine precursor is the stereospecific conversion of HMTBA to the corresponding keto acid. In the present study, the regulation of trans-epithelial HMTBA transport was investigated in Caco-2 cell monolayers. Differentiated Caco-2 cells were maintained under control conditions (apical compartment: 0.2 mmol/L L-methionine) or in a HMTBA-enriched medium (2 mmol/L HMTBA). The effect of culture on HMTBA transport was evaluated from apical and basolateral kinetic parameters. MCT1 and MCT4 immuno-localisation and gene expression were investigated by confocal microscopy and real-time quantitative RT-PCR, respectively. The results indicated that apical MCT1 was up-regulated by exposure to HMTBA (1.4-fold increase in Vmax without changes in Km). Moreover, total monolayer MCT1 immunoreactivity increased 1.8-fold in HMTBA-supplemented cultures, this effect mainly being localised at the apical membrane. Functional and immuno-localisation data suggest involvement of MCT1 and MCT4 in basolateral HMTBA transport, although, in this case, no effect was observed for HMTBA-enrichment. Molecular analysis confirmed MCT1 mRNA up-regulation (1.8-fold), with no effect on MCT4 mRNA expression. Thus, exposure to HMTBA up-regulates the trans-epithelial transport of this methionine precursor by increasing the expression and the transport capacity of apical MCT1.
authors.affiliation: Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, Barcelona E-08028, Spain. Electronic address: raquelmartin@ub.edu.
authors.forename: Raquel
authors.initials: R
authors.lastname: Martín-Venegas
authors.affiliation: Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, Barcelona E-08028, Spain.
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Brufau
authors.affiliation: Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, Barcelona E-08028, Spain.
authors.forename: Oriol
authors.initials: O
authors.lastname: Mañas-Cano
authors.affiliation: Adisseo France S.A.S., CERN, Commentry 03600, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Mercier
authors.affiliation: Adisseo France S.A.S., CERN, Commentry 03600, France.
authors.forename: Magalie K
authors.initials: MK
authors.lastname: Nonis
authors.affiliation: Departament de Fisiologia, Facultat de Farmàcia, Universitat de Barcelona, Av. Joan XXIII s/n, Barcelona E-08028, Spain.
authors.forename: Ruth
authors.initials: R
authors.lastname: Ferrer
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D019587:Dietary Supplements / Q000032:analysis; D006801:Humans; D008715:Methionine / Q000031:analogs & derivatives* / Q000378:metabolism; D027501:Monocarboxylic Acid Transporters / Q000235:genetics* / Q000378:metabolism; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D008715:Methionine; D027501:Monocarboxylic Acid Transporters; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1; C008391:alpha-hydroxy-gamma-methylmercaptobutyric acid
keywords: Apical transport; Basolateral transport; Caco-2 cells; HMTBA; Intestinal absorption