Francoz, Sarah S
02 June 2006
The Mdm2 and Mdm4 oncoproteins are key negative regulators of the p53 tumor suppressor. However, their physiological contributions to the regulation of p53 stability and activity remain highly controversial. Here, we combined a p53 knock-in allele, in which p53 is silenced by a transcriptional stop element flanked by loxP sites, with the Mdm2- and Mdm4-null alleles. This approach allows Cre-mediated conditional p53 expression in tissues in vivo and cells in vitro lacking Mdm2, Mdm4, or both. Using this strategy, we show that Mdm2 and Mdm4 are essential in a nonredundant manner for preventing p53 activity in the same cell type (Mouse Embryonic Fibroblasts (MEFs), neuronal progenitor cells and postmitotic neurons) and irrespective of the proliferation/differentiation status of the cells. Although Mdm2 prevents accumulation of the p53 protein, Mdm4 contributes to the overall inhibition of p53 activity independent of Mdm2. We propose a model in which Mdm2 is critical for the regulation of p53 levels and Mdm4 is critical for the fine-tuning of p53 transcriptional activity, both proteins acting synergistically to keep p53 in check. Finally, we show that neither Mdm2 nor Mdm4 regulate cell cycle progression independently of its ability to modulate p53 function.
Tumors cells grow in nutrient and oxygen-deprived microenvironments and adapt to the suboptimal growth conditions by altering their metabolic pathways. The adaptation process commonly creates a tumor phenotype of high glycolytic potential and aggressive growth characteristics which facilitate metastasis and confer resistance to radiation and chemotherapy. Understanding the mechanisms that allow tumors to adapt and survive in their microenvironment is crucial to cancer prevention and control. It was hypothesized that the tumor microenvironment would induce signaling and enzymatic changes, which if manipulated could improve treatment outcome. The results presented here demonstrate that exposure of tumor cells to chronic low pH or hypoxic conditions induced signaling cascades and altered enzyme profiles which resulted in a pro-survival phenotype. Three key adaptation events were observed and included 1) the up regulation of the metabolic stress and glycolytic proteins AMP-activated protein kinase (AMPK) and 6-Phosphofructo-2-Kinase/Fructose-2,6-Biphosphatase 3 (PFKFB3), respectfully. 2) The upregulation of p53 and 3) changes in the ratios of the bioreductive enzymes were also found to be important in the adaptation. The tumor suppressor p53 played a central role in adaptation because it induced the transcription of anti-glycolytic proteins to control glycolysis and minimize tumor cell acidosis. The ratio of bioreductive enzymes was also altered by changes to the microenvironment. Hypoxia had the greatest effect on protein levels and caused a decrease in the ratio of NAD(P)H:quinone oxidoreductase 1 (NQO1): cytochrome p450 reductase. The increase in cytochrome p450 reductase, a one electron bioreduction enzyme, has been shown to increase toxicity of bioreductive drugs in hypoxic tumors. Micronutrients also had an effect on p53 homeostasis because increasing NQO1 activity by riboflavin supplementation induced a p53-stabilizing effect by enhancing binding of p53 to NQO1, protecting the tumor suppressor from degradation. Taken together, these results indicate the changes that occur in tumor adaptation to the microenvironment require signaling and enzymatic changes that work in concert to regulate metabolism and apoptosis. Many of these changes present therapeutic targets that could be exploited to enhance therapy or prevent adaptation and subsequent tumor growth.
The global burden of cancer has more than doubled in the past 30 years. It is estimated that in 2008, 7 million people worldwide died of cancer. Although the majority of deaths were in adults, 90 000 deaths related to childhood cancers. Childhood cancer comprises all cancers arising in children under the age of 15 years. Cancer in children is fairly rare and globally it is estimated that 160 000 children will be diagnosed with cancer each year (World Health Organization, 2008). Early detection is a fundamental goal in oncology nursing as it provides for early treatment of cancers. The onset in children’s cancers is generally short and if not detected early can grow fast and aggressively. Children’s tumours tend to be more invasive but have a better response to treatment in comparison to adults’ cancer. The purpose of this study is to explore the knowledge of registered nurses practicing at primary health clinics situated in the Johannesburg metropolis regarding the early warning signs of childhood cancer. An exploratory research strategy would be used and a contextual study will be done. The context of the study will be Johannesburg and specifically the primary health clinics in the metropolis. A quantitative survey will be conducted. The population targeted is all registered nurses practicing in the 35 primary health clinics in the Johannesburg Metropolis Region B, D, E, F and D. A census will be done and a self- administered questionnaire will be used to gather self-report data. The data will be analyzed by means of descriptive statistics.
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