Identification of DMP1 as Novel p53 Repressed Transcriptional Target

The transcription factor <i>DMP1</i> is a positive regulator of the tumor suppressor ARF, which in turn controls cell-cycle progression and/or apoptosis through p53. Given the role of DMP1 in the ARF-p53 pathway, we investigated whether the p53 transcription factor might regulate DMP1 expression. We found that endogenous human <i>(h)DMP1</i> mRNA levels were significantly decreased upon induction of the temperature-sensitive p53^Val135 in normal fibroblasts. Consistent with this observation, a p53 knockdown in MCF7 breast cancer cells resulted in increased <i>hDMP1</i> mRNA and protein levels. At the molecular level, we found that p53 directly repressed the hDMP1 promoter activity by up to 90%. This repression was not mediated by p53 binding to the two putative p53-binding sites in the hDMP1 promoter. Instead, deletion analysis revealed a 300bp region containing an EGR1/SP1 binding site that is required for p53-dependent inhibition of hDMP1 promoter activity. Using Sp1-deficient SL2 insect cells, we confirmed that p53-mediated repression of hDMP1 is dependent on Sp1. Furthermore, chromatin immunoprecipitation demonstrated SP1 binding to the hDMP1 promoter. Together, our findings identify an Sp1-dependent, p53-mediated repression of DMP1.