Publications

• Identification and functional characterization of the Caenorhabditis elegans riboflavin transporters rft-1 and rft-2.

  Biswas A., Elmatari D., Rothman J., LaMunyon C.W., Said H.M.

  Two potential orthologs of the human riboflavin transporter 3 (hRFVT3) were identified in the C. elegans genome, Y47D7A.16 and Y47D7A.14, which share 33.7 and 30.5% identity, respectively, with hRFVT3. The genes are tandemly arranged, and we assign them the names rft-1 (for Y47D7A.16) and rft-2 (f ... >> More

  Two potential orthologs of the human riboflavin transporter 3 (hRFVT3) were identified in the C. elegans genome, Y47D7A.16 and Y47D7A.14, which share 33.7 and 30.5% identity, respectively, with hRFVT3. The genes are tandemly arranged, and we assign them the names rft-1 (for Y47D7A.16) and rft-2 (for Y47D7A.14). Functional characterization of the coding sequences in a heterologous expression system demonstrated that both were specific riboflavin transporters, although the rft-1 encoded protein had greater transport activity. A more detailed examination of rft-1 showed its transport of riboflavin to have an acidic pH dependence, saturability (apparent Km = 1.4 ± 0.5 µM), inhibition by riboflavin analogues, and Na(+) independence. The expression of rft-1 mRNA was relatively higher in young larvae than in adults, and mRNA expression dropped in response to RF supplementation. Knocking down the two transporters individually via RNA interference resulted in a severe loss of fertility that was compounded in a double knockdown. Transcriptional fusions constructed with two fluorophores (rft-1::GFP, and rft-2::mCherry) indicated that rft-1 is expressed in the intestine and a small subset of neuronal support cells along the entire length of the animal. Expression of rft-2 is localized mainly to the intestine and pharynx. We also observed a drop in the expression of the two reporters in animals that were maintained in high riboflavin levels. These results report for the first time the identification of two riboflavin transporters in C. elegans and demonstrate their expression and importance to metabolic function in worms. Absence of transporter function renders worms sterile, making them useful in understanding human disease associated with mutations in hRFVT3. << Less

  PLoS ONE 8:E58190-E58190(2013) [PubMed] [EuropePMC]

• Identification and comparative functional characterization of a new human riboflavin transporter hRFT3 expressed in the brain.

  Yao Y., Yonezawa A., Yoshimatsu H., Masuda S., Katsura T., Inui K.

  We isolated cDNA coding a new human riboflavin transporter (hRFT)3, which exhibits 86.7 and 44.1% amino acid identity with hRFT1 and hRFT2, respectively. It was predicted to have 10 putative membrane-spanning domains. The functional characteristics of hRFT3 were examined and compared with those of ... >> More

  We isolated cDNA coding a new human riboflavin transporter (hRFT)3, which exhibits 86.7 and 44.1% amino acid identity with hRFT1 and hRFT2, respectively. It was predicted to have 10 putative membrane-spanning domains. The functional characteristics of hRFT3 were examined and compared with those of its isoforms, hRFT1 and hRFT2. Real-time PCR revealed that hRFT3 mRNA was strongly expressed in the brain and salivary gland. hRFT1 mRNA was strongly expressed in the placenta and small intestine, whereas hRFT2 mRNA was most abundantly expressed in the testis and strongly in the small intestine and prostate. hRFT-mediated uptake of [3H]riboflavin was evaluated using human embryonic kidney 293 cells transiently transfected with the cDNA coding each hRFT. The apparent Michaelis-Menten constants of hRFT1, hRFT2, and hRFT3 for riboflavin were 1.38, 0.98, and 0.33 micromol/L, respectively. The hRFT-mediated [3H]riboflavin uptake was independent of extracellular Na+ and Cl(-). Specific uptake of [3H]riboflavin by hRFT2, but not hRFT1 and hRFT3, decreased as extracellular pH was changed from 5.4 to 8.4. The substrate specificities of the hRFT family were similar. hRFT-mediated uptake of [3H]riboflavin was inhibited by some riboflavin analogs, but not D-ribose, organic ions, or other vitamins. The newly isolated hRFT3 may play an important role in brain riboflavin homeostasis. Its amino acid sequence and functional characteristics are similar to those of hRFT1, but not hRFT2. << Less

  J. Nutr. 140:1220-1226(2010) [PubMed] [EuropePMC]