The European flounder (Platichthys flesus) TP53 functions as a temperature-sensitive transcription factor which inhibits cell growth in yeast

Evolutionary history of the p53 family DNA-binding domain: insights from an Alvinella pompejana homolog

The extremophile Alvinella pompejana, an annelid worm living on the edge of hydrothermal vents in the Pacific Ocean, is an excellent model system for studying factors that govern protein stability. Low intrinsic stability is a crucial factor for the susceptibility of the transcription factor p53 to inactivating mutations in human cancer. Understanding its molecular basis may facilitate the design of novel therapeutic strategies targeting mutant p53. By analyzing expressed sequence tag (EST) data, we discovered a p53 family gene in A. pompejana. Protein crystallography and biophysical studies showed that it has a p53/p63-like DNA-binding domain (DBD) that is more thermostable than all vertebrate p53 DBDs tested so far, but not as stable as that of human p63. We also identified features associated with its increased thermostability. In addition, the A. pompejana homolog shares DNA-binding properties with human p53 family DBDs, despite its evolutionary distance, consistent with a potential role in maintaining genome integrity. Through extensive structural and phylogenetic analyses, we could further trace key evolutionary events that shaped the structure, stability, and function of the p53 family DBD over time, leading to a potent but vulnerable tumor suppressor in humans.

Genetic polymorphism and its potential relation to environmental stress in five populations of the European flounder Platichthys flesus, along the French Atlantic coast

In this study, new DNA markers were explored for the flounder Platichthys flesus. cDNA and genomic sequences of the genes encoding the glyceraldehyde-3-phosphate-deshydrogenase (GAPDH), the cytosolic creatine kinase (CK), the prostaglandin D synthase (PGDS) and the betaine homocysteine methyltransferase (BHMT) were characterized. The tumour suppressor p53 gene structure was already described. A PCR-SSCP (Single Strand Conformation Polymorphism) analysis was finally conducted to study the genetic polymorphism of different populations of flounders collected along the French Atlantic coast. Four highly contaminated French estuaries (Seine, Vilaine, Loire and Gironde) were sampled and compared to a reference estuary (Ster) to explore possible selective effect of the environment on specific allelic frequencies. Our results showed that two loci p53 and PGDS, could be potential markers of chemical stress: p53A allele frequency increased in contaminated systems compared to the reference system. In the Vilaine estuary, PGDS polymorphism could be related to pesticide stress.

Transcriptome profiling the gills of amoebic gill disease (AGD)-affected Atlantic salmon (Salmo salar L.): a role for tumor suppressor p53 in AGD pathogenesis?

Neoparamoeba spp. are amphizoic amoebae with the capacity to colonize the gills of some marine fish, causing AGD. Here, the gill tissue transcriptome response of Atlantic salmon (Salmo salar L.) to AGD is described. Tanks housing Atlantic salmon were inoculated with Neoparamoeba spp. and fish sampled at time points up to 8 days postinoculation (pi.). Gill tissues were taken from AGD-affected fish, and a DNA microarray was used to compare global gene expression against tissues from AGD-unaffected fish. A total of 206 genes, representing 190 unique transcripts, were reproducibly identified as up- or downregulated in response to Neoparamoeba spp. infection. Informative transcripts having GO biological process identifiers were grouped according to function. Although a number of genes were placed into each category, no distinct patterns were observed. One Atlantic salmon cDNA that was upregulated in infected gill relative to noninfected gill at 114 and 189 h pi. showed significant identity with the Xenopus, mouse, and human anterior gradient-2 (AG-2) homologs. Two Atlantic salmon AG-2 mRNA transcripts, designated asAG-2/1 and asAG-2/2, were cloned, sequenced, and shown to be predominantly expressed in the gill, intestine, and brain of a healthy fish. In AGD-affected fish, differential asAG-2 expression was confirmed in samples used for microarray analyses as well as in AGD-affected gill tissue taken from fish in an independent experiment. The asAG-2 upregulation was restricted to AGD lesions relative to unaffected tissue from the same gill arch, while p53 tumor suppressor protein mRNA was concurrently downregulated in AGD lesions. Differential expression of p53-regulated transcripts, proliferating cell nuclear antigen and growth arrest and DNA damage-inducible gene-45beta (GADD45beta) in AGD lesions, suggests a role for p53 in AGD pathogenesis. Thus AGD may represent a novel model for comparative analysis of p53 and p53-regulated pathways.

Lack of p53 induction in fish cells by model chemotherapeutics

Although p53 has been extensively studied in mammalian models, relatively little is known about its specific function in lower vertebrates. It has long been assumed that p53 pathways characterized in mammals apply to other vertebrates as well. Fish provide a useful model for the study of environmental carcinogenesis, and populations of fish inhabiting highly polluted environments provide information on the etiology of pollutant-mediated cancer. In this study, we investigated p53 protein and apoptosis induction in PLHC-1 (desert topminnow hepatocellular carcinoma), RTL-W1 (rainbow trout normal liver), and primary rainbow trout hepatocytes exposed to model chemotherapeutics. All of the chemicals used in these studies have been demonstrated to increase p53 protein levels and induce apoptosis in mammalian cell lines. In contrast, PLHC-1 p53 protein was not induced in response to any model mammalian p53 inducers following 24 h exposures. Additionally, both trout cell types demonstrated this same lack of p53 induction upon exposure to model chemotherapeutic drugs. PLHC-1 cells demonstrated an induction of apoptosis as measured by caspase-3 activation following exposure to all of the chemotherapeutics tested. Our results suggest that fish p53 may be activated differently from that of their mammalian counterparts, and that important differences may exist between phyla in the function and regulation of p53 as well as other mechanisms involved in environmental carcinogenesis.

Functional analysis of p53 tumor suppressor in yeast

The p53 tumor suppressor protein is a transcription factor that mediates the cell's response to various kinds of stress by preventing cell division and/or inducing apoptosis. p53 gene mutations have been detected in nearly 50% of human cancers. These gene aberrations are mostly missense point mutations located predominantly in the central DNA-binding domain. In addition to the classical inactivating mutations, there are also dominant-negative, gain-of-function, temperature-sensitive, and cold-sensitive, discriminating, superactive p53 mutations, and some mutations that do not inactivate p53 activity. Several approaches have been developed for detection and analyses of p53 mutations: first, immunochemical methods have been developed to detect p53 protein levels; second, molecular analyses targeting changes in DNA structure are utilized; and third, functional assays are used to explore the biological properties of the p53 protein. Functional analysis of separated alleles in yeast targets the transactivation capability of the p53 protein expressed in yeast cells. This method uses p53 mRNA isolated from cells and tissues to produce a p53 product by RT-PCR. This method has undergone continuous improvement and now serves as a powerful tool for distinguishing various functional types of p53 mutations. Understanding the exact impact of p53 mutation on its function is an important prerequisite for establishment of efficient anti-cancer therapies.

Functional analysis of chemically-induced mutations at the flounder TP53 locus, the FACIM assay

A functional assay was developed in yeast to identify mutations induced by DNA-damaging agents at the flounder TP53 locus. This assay named FACIM for functional analysis of chemically-induced p53 mutations, is based on the assumption that most genotoxin-induced mutations inactivate transcriptional activity of the TP53 protein. The functional status of the protein expressed in yeast was measured using a p53-responsive reporter gene. The FACIM assay was used to evaluate the mutagenesis of the flounder TP53 exposed in vitro to benzo[a]pyrene diol epoxide (BPDE). A dose-dependent increase of p53 mutation rate was observed with increasing concentrations of BPDE and extension of exposure time. Flounder TP53 gene appeared highly sensitive to point mutations since most of those identified targeted different nucleotides. Mutated base-pairs corresponded predominantly to guanines located on the non-transcribed strand of the DNA. The general distribution of mutations along the flounder TP53 protein was different from that identified in the human homologue suggesting species-differences in mutagenesis of the TP53 gene. Most of flounder TP53 mutants were defective for transactivation and cell growth regulation but some maintained a partial wild-type phenotype. This functional assay in yeast could be used for both evaluation of the genotoxic potency of chemicals or environmental samples and screening of p53 mutations in fish tumours.