A polymorphic microsatellite that mediates induction of PIG3 by p53.

The gene PIG3 is induced by the tumor suppressor p53 but not by p53 mutants unable to induce apoptosis, suggesting its involvement in p53-mediated cell death. Here we show that p53 directly binds and activates the PIG3 promoter, but not through the previously described DNA element. Instead, p53 interacts with a pentanucleotide microsatellite sequence within the PIG3 promoter (TGYCC)n where Y=C or T. Despite its limited similarity to the p53-binding consensus, this sequence is necessary and sufficient for transcriptional activation of the PIG3 promoter by p53 and binds specifically to p53 in vitro and in vivo. In a population of 117 healthy donors from Germany, the microsatellite was found to be polymorphic, the number of pentanucleotide repeats being 10, 15, 16 or 17, and the frequency of alleles 5.1%, 62.0%, 21.4% and 11.5%, respectively. The number of repeats directly correlated with the extent of transcriptional activation by p53. This is the first time that a microsatellite has been shown to mediate the induction of a promoter through direct interaction with a transcription factor. Moreover, this sequence of PIG3 is the first p53-responsive element found to be polymorphic. Inheritance of this microsatellite may affect an individual's susceptibility to cancer.

A promoter that acquired p53 responsiveness during primate evolution.

The tumor suppressor p53 activates the transcription of human PIG3 through direct interaction with a polymorphic microsatellite sequence, (TGYCC)(n). Here, the evolution of this p53-responsive element was recapitulated. Comparison between primate species revealed that the PIG3 promoter acquired this sequence element in its full length only in Hominoidea (apes and humans), whereas the number of TGYCC repeats is far lower in monkeys. Accordingly, only the PIG3 promoters from Hominoidea respond efficiently to p53, whereas those from monkeys respond poorly or not at all. In parallel, the PIG3 gene was strongly induced by p53 in human and chimpanzee cells but was unaffected by p53 in cells derived from a common marmoset monkey. Thus, a novel p53 target gene appeared as recently as during the evolution of primates. This suggests that mechanisms of tumor suppression are subject to ongoing evolution in humans and their closest relatives.

Reactivation of mutant p53 by a one-hybrid adaptor protein.

The most frequent genetic alteration in cancer is a mutation of p53. In most cases, this leads to a sharp increase of the p53 protein levels but abolishes p53's function as an activator of transcription. To correct this defect, wild-type p53 is being reintroduced into tumor cells through gene therapy vectors, thereby inducing cell death. However, this effect is not necessarily specific for tumor cells. Furthermore, mutant p53 in tumor cells trans-dominantly impairs the function of wild-type p53. As an approach to overcome these obstacles, we have developed an adaptor protein that reactivates mutant p53 rather than stimulating transcription on its own. The DNA binding and tetramerizing portions of the p53-homologue p73 were fused to the oligomerization domain of p53. This chimera binds to the DNA of p53-responsive promoters through the p73-derived portions, and it binds to mutant p53 by the p53-derived oligomerization domain. Through this one-hybrid system, mutant p53 is re-enabled to activate transcription. When the adaptor was expressed in tumor cells that contain mutant p53, expression of p53-responsive genes was activated, and growth was inhibited. No such effects were observed in cells that contain wild-type p53 or no p53 at all. When the adaptor was expressed through an adenovirus vector, tumor cells containing mutant p53 were specifically induced to undergo apoptosis. This strategy can turn mutant p53 into an inhibitor of tumor cell growth and might enable gene therapy to eliminate cancer cells with specificity.

p53 induces the expression of its antagonist p73 Delta N, establishing an autoregulatory feedback loop.

The p53 tumor suppressor protein activates transcription and induces cell death. A close homologue of p53, termed p73, is expressed in transactivating (TA) forms that induce growth arrest and apoptosis much like p53. However, the p73 gene contains a second promoter, giving rise to the expression of p73 Delta N, a species of p73 proteins that lack the N-terminal transactivation domain. We show here that the expression of p73 Delta N is induced by p53 on the mRNA and protein level. The promoter that regulates p73 Delta N expression in human cells was cloned and found to be activated by p53, as well as by p73TA, directly through a specific DNA element. The p73 Delta N proteins, that are thereby expressed, bound to p53-responsive promoter DNA, competed with p53 for DNA binding, antagonized the activation of transcription by p53, and prevented p53-induced cell death. In addition, a transcriptional repressor domain was identified within the splicing variant p73 Delta Nalpha. The combination of p73DeltaNalpha and mdm2 antagonized p53 more strongly than either p73Nalpha or mdm2 alone. Blocking endogenous p73 Delta N by a trans dominant fragment, or its removal by siRNA, increased the activity of a p53-responsive promoter in cells that contain a wild type p53 gene. Thus, the induction of p73 Delta N expression by p53 establishes an autoregulatory feedback loop that keeps the trigger of cell death under tight control.

Partial protection against tissue cysts formation in pigs vaccinated with crude rhoptry proteins of Toxoplasma gondii.

A vaccine containing crude Toxoplasma gondii rhoptry proteins incorporated in the immunostimulating complexes (ISCOM) adjuvant was tested in pigs for protecting against tissue cyst formation. For this, 38 mixed breed pigs were divided into four groups, G1 (vaccinated challenged, n=10) received two doses (100 microg/dose) of the rhoptry vaccine at days 0 and 21, G2 (vaccinated challenged, n=10) received viable tachyzoites (7 x 10(7)) of the RH strain at day 0, G3 (unvaccinated challenged, n=10) and G4 (unvaccinated unchallenged, n=8). Pigs were challenged with 4 x 10(4) VEG strain oocysts 57 days later. The G1 pigs produced high IgG antibody levels in the indirect enzyme-linked immunosorbent assay (ELISA) after the second dose of rhoptry vaccine, but were not clinically protected against a high dose oocyst challenge. Partial protection was observed in G1 at the chronic phase of infection, when compared with G3. Pigs in group 2 developed high antibody levels and were protected against clinic signs. T. gondii was not detected in two (G1) and three (G2) pigs by mouse bioassay. The results indicate partial protection in pigs vaccinated with a rhoptry vaccine.

p21/CDKN1A mediates negative regulation of transcription by p53.

The tumor suppressor p53 regulates transcription positively and negatively, depending on the target gene. Whereas p53 induces transcription through direct interaction with promoter DNA, the mechanism of p53-mediated transcriptional repression is less well understood. Early reports described the alleviation of p53-mediated repression by inhibitors of apoptosis, suggesting that negative regulation of transcription might occur only in conjunction with programmed cell death. More recently, it has been proposed that certain genes, such as survivin, are repressed by direct association of p53 with their promoters, followed by recruitment of a repressor complex. We show here that p53-mediated negative regulation of transcription could occur independently of apoptosis. In contrast, the amino-terminal transactivation domain of p53 was required for negative regulation of transcription. Similarly, the p53 homologue p73 diminished the expression of survivin and stathmin, depending on its transactivation domain. Mutation of the putative p53 binding site within the survivin promoter did not impair its repression. These observations raised the hypothesis that activation of an effector gene might be required for repression by p53. Strikingly, when the p53-inducible p21/CDKN1A gene was deleted, p53 no longer repressed any one among 11 genes that it down-regulates otherwise. Most of these genes were also repressed by ectopic p21 in the absence of p53. Overexpressed c-Myc reduced the transcription of p21/CDKN1A and impaired p53-mediated repression but did not abolish repression by ectopic p21. Taken together, these results strongly suggest that increased expression of p21/CDKN1A is necessary and sufficient for the negative regulation of gene expression by p53.

Prevalence of Toxoplasma gondii antibodies in ostriches (Struthio camelus) from commercial breeding facilities in the state of São Paulo, Brazil / Prevalência de anticorpos anti – Toxoplasma gondii em avestruzes (Struthio camelus) de criatórios comerciais no estado de São Paulo

Toxoplasmosis is widespread zoonosis caused by Toxoplasma gondii,a protozoan that may infect mammals and birds. The aim of the present study was to assess the prevalence of T. gondii in ostriches (Struthio camelus) from commercial breeding facilities in the state of São Paulo, Brazil, in a way to increase the knowledge on the behavior and importance of the parasite in this animal species. A total of 195 serum samples were collected from ostriches from Sorocaba, Campinas, São Carlos, Araçatuba, São Paulo, Vale do Ribeira, Botucatu and são José do Rio Preto, in the state of São Paulo. These samples were analyzed by means of the Modified Agglutination Test (MAT)in order to investigate the occurrence of Toxoplasma gondii antibodies. The test showed that 14.36% of the animals were seropositive toToxoplasma gondii. Minimum titer was considered to be equal or greater than 1:16, and the greatest dilution observed was 1:16,384. No statistically significant differences were found between males and females. Seronegative animals occurred in only two regions (São Paulo and São José do Rio Preto). These results point out the importance of further studies on this infection in ostriches, and on management practices that may minimize the risk of toxoplasmosis transmission in these birds which would, in their turn, decrease the risk for the final consumer.

A toxoplasmose é uma zoonose cosmopolita causada pelo protozoário Toxoplasma gondii, podendo acometer mamíferos e aves. O presente estudo teve como objetivo estimar a prevalência do Toxoplasma gondii em avestruzes (Struthio camelus) de criatórios comerciais do estado de São Paulo, como forma de auxiliar no conhecimento do comportamento e importância do parasito nesta espécie animal. Foram colhidas 195 amostras de soro de avestruzes, provenientes de Sorocaba, Campinas, São Carlos, Araçatuba, São Paulo,Vale do Ribeira, Botucatu e São José do Rio Preto, estado de São Paulo. As amostras foram analisadas pela Técnica de Aglutinação Direta Modificada (MAT), para a pesquisa de anticorpos anti – Toxoplasma gondii. Os exames sorológicos revelaram 14,36% de animais sororreagentes ao T. gondii. A titulação mínima considerada foi a diluição maior ou igual a 1:16, e a maior diluição encontrada foi 1:16384.Não foi constatada diferença significativa entre os sexos. Apenas duas regiões (São Paulo e São José do Rio Preto) não apresentaram animais sororreagentes. Esses resultados salientam a importância de um estudo mais aprofundado sobre a infecção em avestruzes, e também sobre as práticas de manejo que venham a minimizar o risco de transmissão da toxoplasmose para essas aves e, por conseqüência,para o consumidor final.