FUNCTIONAL EXPRESSION OF THE NITROBENZYLTHIOINOSINE-SENSITIVE NUCLEOSIDE TRANSPORTER OF HUMAN CHORIOCARCINOMA (BEWO) CELLS IN ISOLATED OOCYTES OF XENOPUS-LAEVIS

被引:6
作者
BOUMAH, CE
HARVEY, CM
PATERSON, ARP
BALDWIN, SA
YOUNG, JD
CASS, CE
机构
[1] UNIV ALBERTA, DEPT BIOCHEM, EDMONTON T6G 2H7, AB, CANADA
[2] UNIV ALBERTA, DEPT PHYSIOL, EDMONTON T6G 2H7, AB, CANADA
[3] UNIV ALBERTA, DEPT PHARMACOL, EDMONTON T6G 2H7, AB, CANADA
[4] UNIV LEEDS, DEPT BIOCHEM & MOLEC BIOL, LEEDS LS2 9JT, W YORKSHIRE, ENGLAND
关键词
D O I
10.1042/bj2990769
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Cultured human choriocarcinoma (BeWo) cells have previously been shown to exhibit, in comparison with other cultured cell types, elevated nitrobenzylthioinosine (NBMPR)-sensitive transport activity and large numbers (> 10(7)/cell) of high-affinity NBMPR-binding sites [Boumah, Hogue and Cass (1992) Biochem. J. 288, 987-996]. The present study investigates whether NBMPR-sensitive nucleoside transport activity could be induced in Xenopus laevis oocytes by microinjection of poly(A)(+) RNA isolated from proliferating cultures of BeWo cells. Expression of uridine transport activity was assayed by comparing rates of uptake (22 degrees C) of 100 mu M [H-3]uridine by RNA-injected oocytes with uptake by water-injected or uninjected oocytes. A 4-fold stimulation of uridine uptake (2.0 versus 0.5 pmol/90 min per oocyte) was seen when oocytes were injected with 50 ng of BeWo poly(A)(+) RNA, and this stimulation was abolished when the RNA-injected oocytes were assayed in the presence of 10 mu M NBMPR. The expressed uridine transport activity in oocytes was highly sensitive to NBMPR, with a 50% reduction seen at 1.1 nM NBMPR (IC50 value). The IC50 value for NBMPR inhibition of uptake of 100 mu M [H-3]uridine by intact BeWo cells was 1.4 nM. Inward fluxes of [H-3]uridine in the RNA-injected oocytes were greatly reduced in the presence of high concentrations (2 mM) of non-radioactive nucleosides (adenosine, thymidine, inosine) that are known permeants of NBMPR-sensitive nucleoside transport processes. These results establish that the abundance of NBMPR-sensitive nucleoside transporter mRNA in poly(A)(+) RNA preparations from BeWo cells is sufficient to achieve production of functionally active transporter protein in Xenopus oocytes and that, when expressed in Xenopus oocytes, the transporters exhibit NBMPR sensitivity and permeant selectively similar to that of the native transporters.
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页码:769 / 773
页数:5
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