CHARACTERIZATION OF THE DEOXYCYTIDINE KINASE PROMOTER IN HUMAN LYMPHOBLAST CELL-LINES

Deoxycytidine kinase (dCK) phosphorylates 2'-deoxycytidine, as well as the purine deoxyribonucleosides and a number of nucleoside analogues that are important in the chemotherapy of leukemias, The enzyme is hig hly expressed in the thymus relative to other tissues and may play an important role in the T cell depletion associated with adenosine deami nase and purine nucleoside phosphorylase deficiencies, To characterize the dCK promoter region and to determine whether it mediates higher l evels of gene expression in T lymphoblasts, we have analyzed a 700-bp genomic fragment encompassing 548 bp of 5' flanking region for functio nal activity and for transcription factor binding using T and B lympho blast cell lines and nuclear extracts, The regions of the promoter tha t were defined as important to its function include a 5'GC box, an E b ox, a 3'GC box, and an E2F site, The transcription factor Spl binds to both GC boxes, activating at the 5' site but repressing at the 3' sit e, MLTF/USF activates transcription through the E box, whereas E2F act ivates through the E2F site, but binds weakly to this site in vitro an d does not appear to mediate cell cycle-specific expression of dCK in vivo, No significant differences in promoter activity or transcription factor binding were observed between Jurkat T and Raji B lymphoblasts , The promoter of the dCK gene is thus regulated by a number of ubiqui tously expressed transcription factors. DCK expression in cultured lym phoblast cell lines is not solely a function of the T or B lineage der ivation.