TRANSCRIPTIONAL REPRESSION OF THE CYCLIN-DEPENDENT KINASE INHIBITOR P21(WAF1 CIP1) GENE MEDIATED BY CIS-ELEMENTS PRESENT IN THE 3'-UNTRANSLATED REGION/

The cyclin-dependent kinase inhibitor p21(WAF1/CIP1) plays a major rol e in the induction of G(1) cell cycle arrest following DNA damage and is known to be regulated by p53-dependent and -independent pathways. H ere, we show that p21(WAF1/CIP1) transcription is also regulated, inde pendently of p53, by the cis elements that are located downstream of t he transcription start site, A cDNA fragment of similar to 180 bp, loc ated 260 bases 3' to the translation termination codon of p21(WAF1/CIP 1) cDNA, was cloned in both the sense and antisense orientations downs tream of the CMV promoter, upstream of the SV40 promoter, and both ups tream and downstream of the p21(WAF1/CIP1) promoter in the plasmids ca rrying the luciferase reporter gene, The constructs were transiently t ransfected in human breast carcinoma cells MCF-7 and MDA-MB-468 and a Syrian hamster smooth muscle cell line DDT1MF2 and were found to elici t 2-3-fold or higher repression of luciferase activities, By using ove rlapping deletions of the above 180-bp fragment, we identified a 48-bp subfragment that contains putative cis element(s) that participate in the transcriptional repression of the p21(WAF1/CIP1) gene, The overla pping subfragments bind, in vitro, to specific proteins present in the nuclear extracts of MDA-MB-468 and DDT1MF2 cells, We, therefore, prop ose that additional mechanism(s) exist that regulate expression of the cellular p21(WAF1/CIP1) and may contribute to p21(WAF1/CIP1)-dependen t control of the cell cycle.