Identification and functional characterization of a novel human and rat riboflavin transporter, RFT1

Atsushi Yonezawa, Satohiro Masuda, Toshiya Katsura, Ken Ichi Inui

Research output: Contribution to journalArticle

94 Citations (Scopus)

Abstract

Absorption of riboflavin is mediated by transporter(s). However, a mammalian riboflavin transporter has yet to be identified. In the present study, the novel human and rat riboflavin transporters hRFT1 and rRFT1 were identified on the basis of our rat kidney mRNA expression database (Horiba N, Masuda S, Takeuchi A, Saito H, Okuda M, Inui K. Kidney Int 66: 29-45, 2004). hRFT1 and rRFT1 cDNAs have an open reading frame encoding 448- and 450-amino acid proteins, respectively, that exhibit 81.1% identity and 96.4% similarity to one another. In addition, an inactive splice variant of hRFT1, hRFT1sv, was also cloned. The hRFT1sv cDNA, which encodes a 167-amino acid protein, retains an intron between exons 2 and 3 of hRFT1. Real-time PCR revealed that the sum of hRFT1 and hRFT1sv mRNAs was expressed strongly in the placenta and small intestine and was detected in all tissues examined. In addition, hRFT1 and hRFT1sv were expressed in human embryonic kidney (HEK)-293 and Caco-2 cells. HEK-293 cells transfected with green fluorescent protein-tagged hRFT1 and rRFT1 exhibited a fluorescent signal in the plasma membrane. Overexpression of hRFT1 and rRFT1, but not hRFT1sv, increased the cellular accumulation of [ 3H]riboflavin. The transfection of small interfering RNA targeting both hRFT1 and hRFT1sv significantly decreased the uptake of [ 3H]riboflavin by HEK-293 and Caco-2 cells. Riboflavin transport is Na+, potential, and pH independent. Kinetic analyses demonstrated that the Michaelis-Menten constants for the uptake by HEK-293 and Caco-2 cells were 28.1 and 63.7 nM, respectively. We propose that hRFT1 and rRFT1 are novel mammalian riboflavin transporters, which belong to a new mammalian riboflavin transporter family.

Original languageEnglish
JournalAmerican Journal of Physiology - Cell Physiology
Volume295
Issue number3
DOIs
Publication statusPublished - Sep 1 2008
Externally publishedYes

Fingerprint

Riboflavin
Kidney
Caco-2 Cells
Complementary DNA
Inteins
Amino Acids
Messenger RNA
Green Fluorescent Proteins
Placenta
Small Interfering RNA
Open Reading Frames
Small Intestine
Transfection
Real-Time Polymerase Chain Reaction
Exons
Cell Membrane
Databases

All Science Journal Classification (ASJC) codes

  • Physiology
  • Cell Biology

Cite this

Identification and functional characterization of a novel human and rat riboflavin transporter, RFT1. / Yonezawa, Atsushi; Masuda, Satohiro; Katsura, Toshiya; Inui, Ken Ichi.

In: American Journal of Physiology - Cell Physiology, Vol. 295, No. 3, 01.09.2008.

Research output: Contribution to journalArticle

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