Transcriptional repression of the human Polycystic Kidney Disease 1 gene by tumor suppressor protein p53
Description
Autosomal Polycystic Kidney Disease (ADPKD) is a common genetic disorder with an incidence of 1 in 500 to 1 in 1000. Most of the ADPKD cases are due to mutations in the Polycystic Kidney Disease-1 gene (PKD1). The PKD1 gene product; Polycystin 1, is involved in cell cycle control and epithelial cell terminal differentiation and PKD1 mutant kidneys manifest cysts formation due to aberrant epithelial cell proliferation and impaired terminal differentiation Previous studies have implicated the tumor suppressor protein/transcription factor p53 as a factor in terminal differentiation of the renal epithelium. The objective of the present study is to investigate the transcriptional regulation of PKD1 by p53 Alteration of endogenous p53 levels effected PKD1 mRNA levels in a negative fashion. Closer analysis of the 5'-regulatory region of the PKD1 gene revealed four putative p53-binding sites (p53BS4-1). P53 was shown to bind these sites both in vitro and in vivo Site-directed mutagenesis of p53BS4-1 53 in a PKD1-promoter reporter construct revealed differential roles of the p53BS's. Partial deletion of the p53BS1 induced baseline PKD1 promoter activity, partial deletion of the p53BS2 reduced activity modestly, partial deletion of the p53BS3 increased activity, and finally partial deletion of the p53BS4 decreased PKD1 baseline promoter activity. Additional mutagenesis experiments revealed that repression mediated through BS1 is dependent on intact BS2-4. Deletion analysis mapped p53-mediated repression to the -200bp proximal promoter region of PKD1, which contains p53BS1. p53BS1 was able to activate reporter gene activity in the context of a heterologous promoter construct and was able to mediate repression of a known p53-target gene -the bradykinin B2 receptor-indicating that p53BS1 functions in the context of a foreign promoter P53-mediated repression of hPKD1 involves recruitment of the mSin3A/HDAC1/2 co-repressor complex, which in the context of the full-length promoter, is partly dependent on p53 binding sites in the distal promoter region These findings, together with previous reports showing that dedifferentiated Pkd1-deficient cells express lower p53 and p21 levels, suggest a model whereby PKD1 signaling activates the p53-p21 differentiation pathway. In turn, p53 cooperates with histone deacetylases to repress PKD1 gene transcription. Loss of a p53-mediated negative feedback loop in PKD1 mutant cells may therefore contribute to deregulated PKD1 expression and cystogenesis