Role of DNA binding cooperativity for tumor suppression by p53

点击翻译按钮获取中文摘要

p53 protects us from cancer by transcriptionally regulating tumor suppressive programs designed to either prevent the development or clonal expansion of malignant cells. Which of these programs are crucial for cancer protection is in the focus of current research, because it is believed that a better mechanistic understanding of tumor suppression by p53 can guide the design of more effective cancer prevention and therapy strategies. In the proposed project we plan to dissect the role of various p53 effector functions for the tumor suppressor activity of p53 with the help of mutations that modulate the DNA binding properties of p53.DNA binding by the tetrameric p53 complex occurs in a cooperative manner that is dependent on interactions between adjacent monomers. Using mutations that reduce or enhance these interactions we were able to alter DNA binding by p53 and showed that p53 effector programs are differently dependent on cooperativity. For example, we have characterized a p53 mutation (p53RR) that reduces DNA binding cooperativity and engineered this mutation into the endogenous p53 gene locus in mice. The p53RR mutation reduced the p53 target gene spectrum as determined by ChIP-sequencing resulting in a severe defect in p53-mediated apoptosis in response to DNA damage and Myc expression. Interestingly, non-apoptotic p53 functions in cell cycle arrest, senescence and metabolism were intact. Despite the profound apoptosis defect, p53RR mice were nevertheless protected from some but not all types of cancer, indicating that p53 uses apoptotic and non-apoptotic effector mechanisms to suppress different types of tumors. In particular, p53RR mice were highly susceptible to Myc- and E1A-induced tumorigenesis. In the course of this project we plan to investigate specifically whether p53RR is sufficient to suppress Ras-driven pancreatic and non-small cell lung cancer.In addition, we have generated a second cooperativity mutant p53EE mouse. In contrast to p53WT and p53RR, p53EE is DNA binding-deficient as determined by ChIP-sequencing, making this mouse an interesting model to study DNA binding-independent tumor suppressor activities of p53. Furthermore, combined expression of p53EE and p53RR rescues cooperativity and generates a p53 heterotetramer with higher than wild-type DNA binding activity. We therefore also plan to analyze compound heterozygous p53EE/RR mice to explore how increased cooperativity influences p53-based cell fate decisions, tumor suppression and aging as a possible side effect of improved tumor suppression.Since the DNA binding cooperativity of p53 is in principle druggable, these experiments are expected to reveal whether modulation of p53 cooperativity could be therapeutically exploited to improve p53 functions in cancer protection and therapy.