TRANSCRIPTIONAL REGULATION OF THE RAT POLY(ADP-RIBOSE) POLYMERASE GENE BY SP1

Expression of the gene encoding poly(ADP-ribose) polymerase (PARP), al though ubiquitous, nevertheless varies substantially between tissues. We have recently shown that Sp1 binds five distinct target sequences ( US-1 and F1-F4) in the rat PARP (rPARP) gene promoter. Here we used de letion analyses and site-directed mutagenesis to address the regulator y function played by these Spl sites on the basal transcriptional acti vity directed by the rPARP promoter. Transfection experiments revealed that the most proximal Spl site is insufficient by itself to direct a ny promoter activity. In addition, a weak negative regulatory element was identified between positions -101 and -60. The rPARP promoter dire cted high levels of chloramphenicol acetyltransferase activity in Jurk at T-lymphoblastoid and Ltk(-) fibroblast cells but only moderate leve ls in pituitary GH4Cl and liver HTC cells, correlating with the amount s of PARP detected in these cells by western blot analysis. However, t he reduced promoter efficiency in HTC and GH4Cl cells did not result f rom the lack of Spl activity in these cells but suggested that yet unc haracterized regulatory proteins might turn off PARP gene expression b y binding negative regulatory elements from the rPARP promoter. Simila rly, site-directed mutagenesis on the three most proximal Spl elements suggested the influence exerted by Spl on the rPARP promoter activity to vary substantially between cell types. It also provided evidence f or a basal rPARP promoter activity driven through the recognition of u nidentified cis-acting elements by transcription factors other than Sp 1.