Identification of a Unique Monocarboxylate Transporter (MCT3) in Retinal Pigment Epithelium

• Published in: Biochemical and biophysical research communications 1997-05, Vol.234 (1), p.90-94
• Main Authors: Yoon, Heeyong, Fanelli, Albertina, Grollman, Evelyn F., Philp, Nancy J.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biological Transport; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Line; Chickens; Cloning, Molecular; DNA, Complementary - genetics; Gene Expression - genetics; Glycosylation; Lactic Acid - metabolism; Microscopy, Fluorescence; Molecular Sequence Data; Pigment Epithelium of Eye - chemistry; Pigment Epithelium of Eye - metabolism; Protons; Pyruvic Acid - metabolism; Rats; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Transfection
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1006/bbrc.1997.6588

The retinal pigment epithelium transports lactate between two tissue compartments, the interphotoreceptor matrix and the choriocapillaris. In this report we describe a 2.45-kb cDNA isolated from a chick cDNA RPE library that encodes a membrane protein found only in RPE cells. The deduced protein has 542 amino acids with twelve putative membrane spanning domains. The cDNA has been designated MCT3 based on its 45% identity in amino acid sequence and structural similarity with the monocarboxylate transporters MCT1 and MCT2. Stable transfectants (pCl-neo/MCT3), made in a rat thyroid epithelial cell line (FRTL-5), express MCT3 RNA. Transfectants had enhanced pyruvate uptake (used as a measure of lactate uptake) which was proton-dependent and inhibited by α-cyano-4-hydroxycinnamate. In summary, MCT3's unique expression in RPE cells, multiple potential phosphorylation sites, and basolateral distribution suggest that MCT3 may regulate lactate levels in the interphotoreceptor space.