ANALYSIS OF THE TPA REGULATORY ELEMENT IN THE GENOMIC POLY(ADP-RIBOSE) SYNTHETASE GENE IN HUMAN LEUKEMIA U937 CELLS

The human leukemia U937 cells differentiate into monocyte/macrophage-l ike cells when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) . We observed that during this process, both protein and mRNA levels f or PARS markedly decreased in U937 cells. Through deletion analysis of the PARS regulatory gene, we found that the sequence within the first intron region was responsible for the TPA-dependent repression. Elect rophoretic mobility shift assays (EMSAs) and Southwestern blot analysi s indicate that this element bound specifically to a nuclear protein, TPA treatment abolished the binding of the protein in U937 cells but n ot in HeLa cells. DNase I footprinting data show that the cis regulato ry element is located between residues 328 and 383. We further examine d the function of this cis element (BS207) in a basal promoter regulat ory reporter construct and found that this cis element (BS207) functio ns as an enhancer via the binding of an unknown trans-acting factor. T PA treatment diminished the binding activity of the factor in U937 cel ls, resulting in a decrease in the enhanced activity to the basal leve l. These results suggest that abolishment of the binding of a special nuclear protein to the first intron of the PARS gene is related to the TPA-responsive downregulation of PARS in U937 cells.