Cloning and pharmacological characterization of a novel gene encoding human nucleoside transporter 1 (hNT1) from a human breast cancer cDNA library.
OBJECTIVE
We isolated a novel gene encoding human nucleoside transporter 1 (hNT1), from a human breast cancer cDNA library.


METHODS
A nondirectional cDNA library was screened by an EST clone (GenBanktrade mark/EMBL/DDBJ: BU944345). A Xenopus laevis oocyte expression system was used for functional characterization. Membrane localization in the human breast was determined by immunohistochemistry.


RESULTS
Isolated hNT1 cDNA consisted of 246 base pairs that encoded an 82-amino acid protein. By RT-PCR analysis, hNT1 mRNA was strongly detected in the breast cancer tissues. When expressed in X. oocytes, hNT1 mediated the high affinity transport of [(3)H]5-fluorouracil (5-FU) with a K(m) value of 69.2+/-24.5 nM in time- and pH-dependent, and Na(+)-independent manners. A cis-inhibition experiment revealed that hNT1 mediated transport of [(3)H]5-FU is strongly inhibited by various nucleosides such as pyrimidine, uracil, uridine, guanosine, inosine, thymidine, adenosine, cytidine and purine suggesting that hNT1 may be involved in the trans epithelial transport of these endogenous substrates. Immunohistochemical analysis revealed that the hNT1 protein is localized in the lactiferous duct epithelium.


CONCLUSIONS
Our present results indicate that a newly isolated cDNA clone, hNT1, is a key molecule for the breast handling of 5-FU in humans.
Umemoto
Takahiro
T
Department of Clinical Pharmacy, School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
Kobayashi
Yasuna
Y
Suzuki
Masako
M
Sanada
Yutaka
Y
Yamamoto
Toshinori
T
D000595:Amino Acid Sequence; D001483:Base Sequence; D001943:Breast Neoplasms / Q000378:metabolism*; D003001:Cloning, Molecular; D005472:Fluorouracil / Q000493:pharmacokinetics; D015723:Gene Library; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D033703:Nucleoside Transport Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology
D033703:Nucleoside Transport Proteins; D005472:Fluorouracil