p53 counteracts reprogramming by inhibiting mesenchymal-to-epithelial transition.

The process of somatic cell reprogramming is gaining increasing interest as reprogrammed cells are considered to hold a great therapeutic potential. However, with current technologies this process is relatively inefficient. Recent studies reported that inhibition of the p53 tumor suppressor profoundly facilitates reprogramming and attributed this effect to the ability of p53 to restrict proliferation and induce apoptosis. Given that mesenchymal-to-epithelial transition (MET) was recently shown to be necessary for reprogramming of fibroblasts, we investigated whether p53 counteracts reprogramming by affecting MET. We found that p53 restricts MET during the early phases of reprogramming and that this effect is primarily mediated by the ability of p53 to inhibit Klf4-dependent activation of epithelial genes. Moreover, transcriptome analysis revealed a large transcriptional signature enriched with epithelial genes, which is markedly induced by Klf4 exclusively in p53(-/-) cells. We also found that the expression of the epithelial marker E-Cadherin negatively correlates with p53 activity in a variety of mesenchymal cells even before the expression of reprogramming factors. Finally, we demonstrate that the inhibitory effect of p53 on MET is mediated by p21. We conclude that inhibition of the p53-p21 axis predisposes mesenchymal cells to the acquisition of epithelial characteristics and renders them more prone to reprogramming. Our study uncovers a novel mechanism by which p53 restrains reprogramming and highlights the role of p53 in regulating cell plasticity.

Evolutionary trade-offs, Pareto optimality, and the geometry of phenotype space.

Biological systems that perform multiple tasks face a fundamental trade-off: A given phenotype cannot be optimal at all tasks. Here we ask how trade-offs affect the range of phenotypes found in nature. Using the Pareto front concept from economics and engineering, we find that best-trade-off phenotypes are weighted averages of archetypes--phenotypes specialized for single tasks. For two tasks, phenotypes fall on the line connecting the two archetypes, which could explain linear trait correlations, allometric relationships, as well as bacterial gene-expression patterns. For three tasks, phenotypes fall within a triangle in phenotype space, whose vertices are the archetypes, as evident in morphological studies, including on Darwin's finches. Tasks can be inferred from measured phenotypes based on the behavior of organisms nearest the archetypes.

Analyses of p53 expression pattern and BRCA mutations in patients with double primary breast and ovarian cancer.

OBJECTIVE: To analyze the somatic pattern of p53 expression and BRCA germline mutation status in Israeli patients with both ovarian (OvCa) and breast cancer (BrCa). METHODS: The study group comprised 43 Israeli patients with OvCa, all of whom had previous primary BrCa. p53 immunohistochemistry (IHC) on all available archival tissues and genotyping for the three predominant Jewish germline BRCA1-2 mutations were carried out. Samples from 64 patients with solitary OvCa and 61 with solitary BrCa were similarly analyzed as controls. RESULTS: p53 expression pattern and the immunopositivity rate were similar in the ovarian and breast tumors within the study group and in the two control groups: positive p53 staining was detected in 68% of ovarian tumors in the study group compared with 71.9% in the controls, and in 19.4% of the BrCa tissues versus 21.3% in the controls. Within the study group, advanced stage OvCa had a higher rate of p53 expression (84%) compared to early stage disease (38.5%) (P = 0.006). This difference was not apparent in the solitary OvCa control group. OvCa in BRCA1-2 mutation carriers from the study group were more likely to display positive p53 staining (79%), especially in tumors diagnosed before the age of 60 (90%) compared with the OvCa of noncarriers (60%), but this difference was statistically insignificant. The p53 expression rate in BrCa samples from the study group was not associated with BRCA1-2 mutation status. CONCLUSIONS: Positive p53 expression, detected by IHC, in OvCa patients with previous primary BrCa is significantly higher in advanced stage disease in BRCA1-2 mutation carriers. There is a higher positive p53 expression somatically in OvCa in BRCA1-2 carriers in whom OvCa was diagnosed before the age of 60 years, although this trend is not statistically significant. These observations suggest that somatic p53 inactivation may be an important event in ovarian tumorigenesis in this subset of patients.

Patients with double primary tumors in the breast and ovary- clinical characteristics and BRCA1-2 mutations status.

OBJECTIVE: The aim of this study was to define the prevalence, clinical characteristics, and BRCA1-2 mutation carrier status of ovarian cancer (OvC) patients with a previous primary malignancy in the breast (PPMBr). METHODS: The study population comprised 1240 consecutive Jewish Israeli women with pathologically confirmed epithelial OvC diagnosed between March 1, 1994, and December 31, 1997. Demographic and clinical data were obtained from medical files and from a detailed questionnaire taken through a nationwide epidemiological case-control study on OvC. Blood samples and tumor tissues were collected for analysis of the three predominant germline BRCA1-2 Jewish founder mutations (185delAG, 5382insC, and 6174delT). RESULTS: Fifty nine (4.7%) patients with OvC had a PPMBr. The median age at diagnosis of OvC was 60 years. The mean interval between the two diagnoses was 104 months (range 0-363 months). In the majority of the patients (n = 53), the diagnosis of breast cancer (BrC) preceded the OvC by more than 1 year. The ovarian tumors were diagnosed in 47% of the cases following investigation of patients' symptoms. In 41%, diagnosis was made as a consequence of check-up exams performed during the routine follow-up of BrC survivors. Patients with PPMBr were more likely to present with FIGO ovarian stage III-IV, compared to women with solitary OvC (73% vs 60. 3%, P < 0.05), and less likely to have borderline tumors (3.4% vs 17. 9%, P = 0.007). Family history of OvC/BrC was recorded in 26% of this group of patients compared to 10.5% among patients with solitary OvC (P = 0.003). Patients with PPMBr had an exceptionally high prevalence of BRCA1-2 mutations (57%), irrespective of family history. CONCLUSIONS: Patients with PPMBr present with more advanced disease and invasive-type epithelial ovarian tumors when compared to cases associated with solitary OvC. The rate of BRCA1-2 mutations in Jewish women with OvC who had PPMBr is at least twice as high as in Jewish women with OvC as the solitary disease.