Identification and Comparative Functional Characterization of a New Human Riboflavin Transporter hRFT3 Expressed in the Brain
Identification and Comparative Functional Characterization of a New Human Riboflavin Transporter hRFT3 Expressed in the Brain
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DOI：
10.3945/jn.110.122911
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发表时间：
2010-07-01
影响因子：
4.2
通讯作者：
Inui, Ken-ichi
中科院分区：
文献类型：
--
作者：
Yao, Yoshiaki;Yonezawa, Atsushi;Inui, Ken-ichi
我们克隆了一个新的人核黄素转运蛋白(HRFT)3的编码基因，它与hRFT1和hRFT2的氨基酸同源性分别为86.7%和44.1%。它被预测有10个假定的跨膜结构域。检测了hRFT3的功能特性，并与其异构体hRFT1和hRFT2进行了比较。实时定量聚合酶链式反应显示，hRFT3mRNA在脑和唾液腺中有较强的表达。HRFT1在胎盘和小肠中表达最强，而hRFT2在睾丸中表达最丰富，在小肠和前列腺中表达最强。HRFT介导的[H-3]核黄素摄取被瞬时转染人胚胎肾293细胞的[H-3]核黄素检测。核黄素对hRFT1、hRFT2和hRFT3的表观米氏常数分别为1.38、0.98和0.33mU·mol/L。HRFT介导的[H-3]核黄素摄取不依赖于胞外NaL(+)和CI-。当胞外pH从5.4改变到8.4时，hRFT2对[H-3]核黄素的特异性摄取减少，但hRFT1和hRFT3并不如此。HRFT家族的底物特异性相似。核黄素类似物可抑制hRFT介导的核黄素摄取，但D-核糖、有机离子或其他维生素不能抑制核黄素的摄取。新分离的hRFT3基因可能在脑内核黄素稳态中起重要作用。其氨基酸序列和功能特征与hRFT1相似，但与hRFT2不同。J.Nutr.140：1220-1226,2010。
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 [H-3]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 mu mol/L, respectively. The hRFT-mediated[H-3]riboflavin uptake was independent of extracellular Nal(+) and CI-. Specific uptake of [H-3]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 [H-3]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. J. Nutr. 140: 1220-1226, 2010.