Cloning of a novel isoform of the mouse NBMPR-sensitive equilibrative nucleoside transporter (ENT1) lacking a putative phosphorylation site

We have isolated a mouse cDNA clone corresponding to a novel isoform of the NBMPR-sensitive equilibrative nucleoside transporter (ENT1). The cDNA cont ains a 6 bp deletion in the open reading frame that changes the amino acid composition in a consensus casein kinase II (CKII) phosphorylation site at Ser-254. The clone containing Ser-254 is termed mENT1.1 and the clone lacki ng the serine termed mENT1.2. The deduced amino acid sequence of mENT1.1 co rresponds to the previously cloned human and rat ENT1 proteins at Ser-254. Tissue distribution studies show that mRNA for both ENT1 isoforms are ubiqu itously co-expressed in mouse. Analysis of genomic DNA corresponding to mou se ENT1 indicates the isoforms can be produced by alternative splicing at t he end of exon 7. CEM/C19 cells stably expressing mENT1.1 and mENT1.2 show similar dose response curves for NBMPR and dipyridamole inhibition of [H-3] adenosine uptake as well as exhibiting comparable selectivity for both puri ne and pyrimidine nucleosides but not the corresponding nucleobases. (C) 20 01 Elsevier Science B.V. All rights reserved.