Pierre May

Twenty years of p53 research: structural and functional aspects of the p53 protein

From its modest beginnings in 1979, as a transformation-associated protein, to the discoveries that p53 plays a key role in tumour suppression and in the cellular response to DNA damage, p53 has risen to molecular superstardom both in the research community and in the large public. The aim of this review is to relate how the p53 history has unfolded until now, and to underscore our present knowledge of this paradigmatic protein. To attempt coverage of all aspects of p53 would be unrealistic. Rather, we restrict our considerations to the properties of p53 as tumour suppressor and as cell cycle regulator activated by DNA damage, emphasizing the relationship between structure and function of the p53 protein.

Further characterisation of the p53 responsive element – identification of new candidate genes for trans -activation by p53

The p53 protein is known to trans-activate a number of genes by specific binding to a consensus sequence containing two decamers of the type: PuPuPuCA/TT/AGPyPyPy. In order to identify new p53 trans-activated genes, we defined a set of criteria for computer search of p53-responsive elements. Based on experimental data, we proposed an extended consensus sequence composed of the two decamers of the El-Deiry consensus sequence flanked by two additional ones. A maximum of 3 bp substitutions was accepted for the two decamers of the El-Deiry consensus sequence, as well as for each additional decamer, except when the two decamers of the El-Deiry consensus sequence are contiguous. In this case, each additional decamer is allowed to bear one base insertion or deletion between the median C and G. This set of criteria was validated by identifying within the promoter region of the IGF-BP3 gene the existence of a novel p53-responsive element whose functional significance was verified. By limiting our computer search to Vertebrate genes involved in cell cycle regulation, cellular adhesion or metastatic processes and to gene families most often found in HOVERGEN database, 7785 gene sequences were first analysed. Among the oncogenes, kinases, proteases and structural proteins, 55 new genes were selected; six of them were retrieved in more than one species

Prolonged p53 protein accumulation in trichothiodystrophy fibroblasts dependent on unrepaired pyrimidine dimers on the transcribed strands of cellular genes.

Trichothiodistrophy (TTD), xeroderma pigmentosum (XP), and Cockaynes syndrome (CS) are three distinct human diseases with sensitivity to ultraviolet (UV) radiation affected by mutations in genes involved in nucleotide excision repair (NER). Among the many responses of human cells to UV irradiation, both nuclear accumulation of p53, a tumor suppressor protein, and alterations in cell‐cycle checkpoints play crucial roles. The purpose of this study was to define the signals transmitted after UV‐C–induced DNA damage, which activates p53 accumulation in TTD/XP‐D fibroblasts, and compare this with XP‐D cell lines that carry different mutations in the same gene, XPD. Our results showed that p53 was rapidly induced in the nuclei of TTD/XP‐D and XP‐D fibroblasts in a dose‐dependent manner after UV‐C irradiation, as seen in XP‐A and CS‐A fibroblasts, much lower doses being required for the protein accumulation than in normal human fibroblasts, XP variant cells, and XP‐C cells. The kinetics of accumulation of p53 and two effector proteins involved in cell‐cycle arrest, WAF1 and GADD45, were also directly related to the repair potential of the cells, as in normal human fibroblasts their levels declined after 24 h, the time required for repair of UV‐induced lesions, whereas NER‐deficient TTD/XP‐D cells showed p53, WAF1, and GADD45 accumulation for over 72 h after irradiation. Our results indicate that p53 accumulation followed by transcriptional activation of genes implicated in growth arrest is triggered in TTD/XP‐D cells by the persistence of cyclobutane pyrimidine dimers, which are known to block transcription, on the transcribed strands of active genes. Mol. Carcinog. 20:340–347, 1997.

Immunological evidence for the association between Simian Virus 40 115-kDa super T antigen and hsp70 proteins in rat, monkey, and human cells

Immunological evidence was provided that in subclone 7 cell line, which is derived from SV40 transformed cells, 115-kDa super T antigen, a transformation-competent, elongated form of large T antigen was physically complexed with hsp70 proteins. This conclusion was first based on the coimmunoprecipitation from unstressed or heat shocked subclone 7 cells of both super T antigen and hsp70 proteins. This was observed with any one of a set of anti-T monoclonal antibodies reacting to determinants located either in the C-terminal region or in the N terminal region. Reciprocally coimmunoprecipitation of both hsp70 and super T was also observed in the anti-hsp70 peptide serum-immunoprecipitate. The formation of complexes between hsp70 proteins and super T antigen in subclone 7 cells was also confirmed by Western blot experiments. Moreover, when expressed in cell lines originating from human (Hela cells) or monkey (CV1P cells) species following transfection with the relevant plasmid, super T antigen again displayed the ability to associate with hsp70 proteins. Considering that super T antigen was obtained in laboratory experiments as a stable evolutionary variant of SV40 large T antigen, it is suggested that the marked ability of super T antigen to associate with heat shock protein could be selectively advantageous under certain conditions.