5-Lipoxygenase is a direct p53 target gene in humans.

The p53 tumor suppressor plays a critical role in cancer, and more than 50% of human tumors contain mutations or deletions of the TP53 gene. p53 can transactivate or repress target genes in response to diverse stress signals, such as transient growth arrest, DNA repair, cellular differentiation, senescence and apoptosis. Through an unbiased genome-wide ChIP-seq analysis, we have found that 5-lipoxygenase (ALOX5, 5-LO) which is a key enzyme of leukotriene (LT) biosynthesis, is a direct target gene of p53 and its expression is induced by genotoxic stress via actinomycin D (Act.D) or etoposide (Eto) treatment. 5-LO and LTs play a role in immunological diseases as well as in tumorigenesis and tumor growth. p53 binds to a specific binding site consisting of a complete p53 consensus-binding motif in ALOX5 intron G which is located about 64kbp downstream of the transcriptional start site. We confirmed the strong binding of p53 to the 5-LO target site in ChIP-qPCR experiments. Expression analyses by qRT-PCR and immunoblot further revealed that genotoxic stress induces the ALOX5 mRNA and protein expression in a p53-dependent manner. Knockdown of p53 in U2OS cells leads to a downregulation of 5-LO mRNA and protein expression. In addition, immunofluorescence and immunoprecipitation assays indicate the direct binding of 5-LO to p53 protein. Furthermore, we found that 5-LO can inhibit the transcriptional activity of p53 suggesting that 5-LO acts in a negative feedback loop to limit induction of p53 target genes.

Resveratrol-induced potentiation of the antitumor effects of oxaliplatin is accompanied by an altered cytokine profile of human monocyte-derived macrophages.

The objective of this study was to investigate, whether the naturally occurring polyphenol resveratrol (Res) enhances the anti-tumor activities of the chemotherapeutic agent oxaliplatin (Ox) in a cell culture model of colorectal cancer, also with regard to a possible inflammatory response and cytotoxic side-effects. Res and Ox in combination synergistically inhibit cell growth of Caco-2 cells, which seems to be due to the induction of different modes of cell death and further leads to an altered cytokine profile of cocultured macrophages. Moreover, combinatorial treatment does not affect non-transformed cells as severe cytotoxicity is not detected in human foreskin fibroblasts and platelets.

Role of p53 serine 46 in p53 target gene regulation.

The tumor suppressor p53 plays a crucial role in cellular growth control inducing a plethora of different response pathways. The molecular mechanisms that discriminate between the distinct p53-responses have remained largely elusive. Here, we have analyzed the p53-regulated pathways induced by Actinomycin D and Etoposide treatment resulting in more growth arrested versus apoptotic cells respectively. We found that the genome-wide p53 DNA-binding patterns are almost identical upon both treatments notwithstanding transcriptional differences that we observed in global transcriptome analysis. To assess the role of post-translational modifications in target gene choice and activation we investigated the genome-wide level of phosphorylation of Serine 46 of p53 bound to DNA (p53-pS46) and of Serine 15 (p53-pS15). Interestingly, the extent of S46 phosphorylation of p53 bound to DNA is considerably higher in cells directed towards apoptosis while the degree of phosphorylation at S15 remains highly similar. Moreover, our data suggest that following different chemotherapeutical treatments, the amount of chromatin-associated p53 phosphorylated at S46 but not at pS15 is higher on certain apoptosis related target genes. Our data provide evidence that cell fate decisions are not made primarily on the level of general p53 DNA-binding and that post-translationally modified p53 can have distinct DNA-binding characteristics.