Monocarboxylate transporter 1 is up-regulated in Caco-2 cells by the methionine precursor DL-2-hydroxy-(4-methylthio)butanoic acid

• Published in: The veterinary journal (1997) 2014-12, Vol.202 (3), p.555-560
• Main Authors: Martín-Venegas, Raquel, Brufau, M.Teresa, Mañas-Cano, Oriol, Mercier, Yves, Nonis, Magalie K., Ferrer, Ruth
• Format: Article
• Language: English
• Subjects: Apical transport; Basolateral transport; Biological Transport; Caco-2 Cells; Dietary Supplements - analysis; HMTBA; Humans; Intestinal absorption; Methionine - analogs & derivatives; Methionine - metabolism; Monocarboxylic Acid Transporters - genetics; Monocarboxylic Acid Transporters - metabolism; Symporters - genetics; Symporters - metabolism; Up-Regulation
• ISSN: 1090-0233; 1532-2971
• DOI: 10.1016/j.tvjl.2014.09.019

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.