Clonal hematopoiesis of indeterminate potential (CHIP) increases with age and is associated with increased risks of hematological malignancies. While TP53 mutations have been identified in CHIP, the molecular mechanisms by which mutant p53 promotes hematopoietic stem and progenitor cell (HSPC) expansion are largely unknown. Here we discover that mutant p53 confers a competitive advantage to HSPCs following transplantation and promotes HSPC expansion after radiation-induced stress. Mechanistically, mutant p53 interacts with EZH2 and enhances its association with the chromatin, thereby increasing the levels of H3K27me3 in genes regulating HSPC self-renewal and differentiation. Furthermore, genetic and pharmacological inhibition of EZH2 decreases the repopulating potential of p53 mutant HSPCs. Thus, we uncover an epigenetic mechanism by which mutant p53 drives clonal hematopoiesis. Our work will likely establish epigenetic regulator EZH2 as a novel therapeutic target for preventing CHIP progression and treating hematological malignancies with TP53 mutations.

24Clonal hematopoiesis of indeterminate potential (CHIP) increases with age and is associated 25 with increased risks of hematological malignancies. While TP53 mutations have been 26 identified in CHIP, the molecular mechanisms by which mutant p53 promotes hematopoietic 27 stem and progenitor cell (HSPC) expansion are largely unknown. We discovered that mutant 28 p53 confers a competitive advantage to HSPCs following transplantation and promotes 29 HSPC expansion after radiation-induced stress. Mechanistically, mutant p53 interacts with 30 EZH2 and enhances its association with the chromatin, thereby increasing the levels of 31 H3K27me3 in genes regulating HSPC self-renewal and differentiation. Further, genetic and 32 pharmacological inhibition of EZH2 decrease the repopulating potential of p53 mutant 33HSPCs. Thus, we have uncovered an epigenetic mechanism by which mutant p53 drives 34 clonal hematopoiesis. Our work will likely establish epigenetic regulator EZH2 as a novel 35 therapeutic target for preventing CHIP progression and treating hematological malignancies 36 with TP53 mutations. 37 38 39 40 4 Clonal hematopoiesis of indeterminate potential (CHIP), also known as age-related clonal 41 hematopoiesis (ARCH), occurs when a single mutant hematopoietic stem and progenitor cell 42 (HSPC) contributes to a significant clonal proportion of mature blood lineages during aging 1-43 3 . CHIP is common in aged healthy individuals and associated with increased risks of de 44 novo and therapy-related hematological neoplasms, including myelodysplastic syndromes 45 (MDS) and acute myeloid leukemia (AML) 4-8 . CHIP is also associated with increased all-46 cause mortality and risk of cardio-metabolic disease [4][5][6] 9 . While these findings suggest that 47 mutations identified in CHIP likely drive disease development, mechanisms by which these 48 mutations promote HSPC expansion are largely unknown [4][5][6][7][8][9] . 49Most individuals with CHIP carry hematological malignancy-associated mutations, 50including DNMT3A, TET2, ASXL1, JAK2, and TP53 4-6 . The TP53 gene, which encodes the 51 tumor suppressor protein p53, ranks in the top five among genes that were mutated in CHIP 52 4-6, 10-12 . p53 bears the usual hallmarks of a transcription factor, with an amino-terminal 53 transactivation domain (TAD), a core DNA-binding domain (DBD) and carboxy-terminal 54 tetramerization (TET) and regulatory domains (REG) [13][14] . It regulates a large number of 55 genes in response to a variety of cellular insults, including oncogene activation, DNA 56 damage, and inflammation, to suppress tumorigenesis [13][14] . TP53 mutations and deletions 57 were found in approximately half of all human cancers, including hematological malignancies 58 [13][14] . Recently, somatic TP53 mutations were identified in CHIP 4-6 . TP53 mutations were 59 also commonly found in therapy-related CHIP 10, 12 . Interestingly, some individuals with Li-60Fraumeni syndrome (LFS), who carry germline TP53 mutations, develop MDS and AML as 61 they age [14][15] . I...

Metastasis of cancer cells to distant organ systems is a complex process that is initiated with the programming of cells in the primary tumor. The formation of distant metastatic foci is correlated with poor prognosis and limited effective treatment options. We and others have correlated Mouse double minute 2 (Mdm2) with metastasis; however, the mechanisms involved have not been elucidated. Here, it is reported that shRNA-mediated silencing of Mdm2 inhibits epithelial-mesenchymal transition (EMT) and cell migration. analysis demonstrates that silencing Mdm2 in both post-EMT and basal/triple-negative breast cancers resulted in decreased primary tumor vasculature, circulating tumor cells, and metastatic lung foci. Combined, these results demonstrate the importance of Mdm2 in orchestrating the initial stages of migration and metastasis. Mdm2 is the major factor in the initiation of metastasis. .

The transcription factors p53 and p73 are critical to the induction of apoptotic cell death, particularly in response to cell stress that activates c-Jun N-terminal kinase (JNK). Mutations in the DNA-binding domain of p53, which are commonly seen in cancers, result in conformational changes that enable p53 to interact with and inhibit p73, thereby suppressing apoptosis. In contrast, wild-type p53 reportedly does not interact with p73. We found that JNK-mediated phosphorylation of Thr in the proline-rich domain (PRD) of p53 enabled wild-type p53, as well as mutant p53, to form a complex with p73. Structural algorithms predicted that phosphorylation of Thr exposes the DNA-binding domain in p53 to enable its binding to p73. The dimerization of wild-type p53 with p73 facilitated the expression of apoptotic target genes [such as those encoding p53-up-regulated modulator of apoptosis (PUMA) and Bcl-2-associated X protein (BAX)] and, subsequently, the induction of apoptosis in response to JNK activation by cell stress in various cells. Thus, JNK phosphorylation of mutant and wild-type p53 promotes the formation of a p53/p73 complex that determines cell fate: apoptosis in the context of wild-type p53 or cell survival in the context of the mutant. These findings refine our current understanding of both the mechanistic links between p53 and p73 and the functional role for Thr phosphorylation.

Mutations in the tumor suppressor TP53 are rare in renal cell carcinomas. p53 is a key factor for inducing anti-angiogenic genes and RCC are highly vascularized, which suggests that p53 is inactive in these tumors. One regulator of p53 is the Mdm2 oncogene, which is correlated with high-grade, metastatic tumors. However, the sole activity of Mdm2 is not just to regulate p53, but it can also function independent of p53 to regulate the early stages of metastasis. Here, we report that the oncoprotein Mdm2 can bind directly to the tumor suppressor VHL, and conjugate nedd8 to VHL within a region that is important for the p53-VHL interaction. Nedd8 conjugated VHL is unable to bind to p53 thereby preventing the induction of anti-angiogenic factors. These results highlight a previously unknown oncogenic function of Mdm2 during the progression of cancer to promote angiogenesis through the regulation of VHL. Thus, the Mdm2-VHL interaction represents a pathway that impacts tumor angiogenesis.