Transcriptional regulation of the human DNA polymerase delta catalytic subunit gene POLD1 by p53 tumor suppressor and Sp1.


The DNA polymerase delta catalytic subunit gene (POLD1) was studied as ...
The DNA polymerase delta catalytic subunit gene (POLD1) was studied as a transcriptional target of p53. Northern blotting showed that a significantly decreased steady-state level of POLD1 mRNA was associated with increased wild-type p53 expression in cells treated with methyl methanesulfonate. When ectopic wild-type p53 expression was induced to a physiologically relevant level in "tet-off" cultured cells in which p53 expression was tightly regulated by tetracycline, it was found that POLD1 steady-state mRNA was repressed by about 65%. Transient cotransfection experiments using a POLD1 promoter luciferase reporter construct showed that: (i) POLD1 promoter activity was inhibited by transfected wild-type p53 plasmid to a maximum of about 86%; (ii) p53 mediated a large part of the transcriptional repression through a sequence-specific interaction with a site identified as the P4 site of the POLD1 promoter; (iii) tumor-derived p53 mutations in the p53 DNA-binding domain completely abolished the p53 transrepression activity. Moreover, transfection assays demonstrated that p53 was able to repress Sp1-stimulated POLD1 promoter activity and that this repression was largely due to the loss of the sequence-specific interaction between Sp1 protein and the P4 Sp1-binding site, which overlaps the P4 p53-binding site. Finally, gel shift assays suggested that p53 competes with Sp1 protein for binding to the P4 sequence of the POLD1 promoter.




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