p53 regulates DREAM complex-mediated repression in a p21-independent manner.

The DREAM repressor complex regulates genes involved in the cell cycle and DNA repair, vital for maintaining genome stability. Although it mediates p53-driven repression through the canonical p53-p21-Rb axis, the potential for p53 to directly regulate DREAM targets independently of its transcriptional activity has not been explored. Here, we demonstrate that in asynchronously growing cells, p53 loss leads to greater de-repression of DREAM targets compared to p21 loss alone. Both wild-type and transactivation-deficient p53 mutants are capable of repressing DREAM targets, suggesting a transactivation-independent "non-canonical" repression mechanism. These p53 variants bind p130/p107, irrespective of their phosphorylation status, while cancer-associated p53 mutants disrupt DREAM complex function by sequestering E2F4. Re-ChIP analysis shows co-recruitment of p53 and E2F4 to known and newly identified DREAM target promoters, indicating direct repression of these targets by p53. These findings reveal a novel, transactivation-independent mechanism of p53-mediated repression, expanding our understanding of p53's tumor-suppressive functions and suggesting DREAM complex targeting as potential future avenues in cancer therapy.