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and K.H.Y. factor in overall DLBCL. Both MDM2 and p53 overexpression do not predict for an adverse clinical outcome in patients with wild-type p53 Cefuroxime sodium but predicts for significantly poorer survival in patients with mutated p53. Variable p53 activities may ultimately determine the survival differences, as suggested by the gene expression profiling analysis. amplification was observed in 3 of 364 (0.8%) patients with high MDM2 expression. The presence of SNP309 did not correlate with MDM2 expression and survival. This study indicates that evaluation of MDM2 and p53 expression correlating with Cefuroxime sodium genetic status is essential to assess their prognostic significance and is important for designing therapeutic strategies that target the MDM2-p53 interaction. Introduction MDM2/Hdm2, the human homolog of murine double minute 2 (Mdm2) or p53 E3 ubiquitin protein ligase homolog (mouse) (gene is transactivated by p53, and thus p53 degradation by MDM2 forms the other direction of a negative-feedback loop. MDM2 is frequently overexpressed in cancer, but its prognostic importance has been elusive in many disease entities.3 MDM2 overexpression has been shown to facilitate B-cell lymphomagenesis in vivo4 and to inactivate the tumor suppressor function Cefuroxime sodium of wild-type p53 (WT-p53) in vitro.5 MDM2 overexpression, however, has correlated inconsistently with adverse clinical outcomes in patients with hematologic malignancies.6,7 Several factors could account for the inconsistent results: (1) Small study sizes; (2) different cutoffs for MDM2 expression; (3) unclear expression and function of MDM2 isoforms8; and (4) posttranslational modifications or subcellular localization of MDM2.3 In stress conditions, both p53 and MDM2 are modified (eg, phosphorylation by ATM), resulting in Rabbit Polyclonal to PNPLA8 reduced affinity and increased degradation of MDM2.9 In addition, MDM2 nuclear entry is inhibited via induction of p53-responsive PTEN,10 and p53-inducible p21 maintains another positive feedback loop.11 A fifth possible factor is oscillation of the p53-MDM2 autoregulatory feedback loop (Figure 1C), which has not been recognized by the previous prognostic studies. Elegant models and laboratory observations have shown that cellular levels of WT-p53 and MDM2 fluctuate in an oscillatory fashion in response to stress, such as DNA damage, hypoxia, or oncogene activation, and that the numbers of pulses and the fraction of cells with oscillatory pulses increase with the strength of DNA damage.9-23 The oscillatory kinetics and the variable amplitude of p53/MDM2 pulses over cell population may affect the measurement of MDM2 expression using immunohistochemistry (IHC), a commonly used method in clinical diagnostic and prognostic studies. If the study cohort is too small, or the cutoff is inappropriately established, the survival difference between 2 groups may not be truly reflected. To obtain evaluable results beyond the noise caused by oscillation, a large cohort of cases is essential. Open in a separate window Figure 1 MDM2 and p53 expression in DLBCL patients treated with R-CHOP. (A-B) Histogram showing the distribution of MDM2 and p53 expression levels in the DLBCL cohort. X-axis, percentage of immunopositive cells in tumors; Y-axis, numbers of DLBCL patients. (C) Illustration of p53 and MDM2 kinetic pulses in tumor cells under stress conditions. In a single cell, because of the fluctuating p53/MDM2 levels in oscillatory pulses, the IHC pattern is (1) p53C/MDM2C at zero time point A or E after cellular stress is removed; (2) p53+/MDM2+ at time point B; (3) p53C/MDM2+ at time point C; and (4) p53+/MDM2C at time point D. Same patterns over cell population may be generated by evaluation of the percentage of MDM2+ cells and defining overexpression by certain cutoffs. (D) Representative MDM2 immunohistochemical staining patterns. In comparison, MDM2 function toward mutant p53 (MUT-p53) and the kinetics of MDM2 and MUT-p53 levels under stress are not well defined. In a mouse model, MDM2 and DNA damage regulate MUT-p53 levels in a manner similar to WT-p53.24 However, most MUT-p53s have lost the ability to transactivate promoter is associated with an increased affinity with the transcriptional activator Sp1, resulting in elevated MDM2 expression, in a gender-specific (females) and hormonal-dependent manner.32,33 On the other hand, in Burkitt lymphoma cells, MDM2 overexpression was caused by enhanced translation.5 To explore the prognostic significance of MDM2 expression and mechanisms of MDM2 overexpression, and to recognize the possible factors that could complicate the analysis of the results,.