RESUMO
BACKGROUND: We reported previously that nearly all human neuroblastomas analyzed contain and express genomic DNA sequences deriving from the human polyomavirus BK (BKV) [Flaegstad et al.: Cancer Res 59:1160-1163, 1999]. PROCEDURE: Here we show that the BKV large T antigen is expressed and bound to p53 in neuroblastoma cells and that this interference compromises the tumor suppressor function of p53. RESULTS: Treatment of neuroblastoma cells with large T antigen antisense constructs relocated active p53 to the nucleus. The relocation event was accompanied by enhanced p21(waf1/cip1) expression as well as induced apoptosis. CONCLUSIONS: Continuous antisense oligonucleotide treatment of nude rats with human neuroblastoma xenografts resulted in a significant but incomplete reduction of tumor growth compared to rats treated with saline.
Assuntos
Antígenos Transformantes de Poliomavirus/análise , Antígenos Transformantes de Poliomavirus/imunologia , Genes p53/imunologia , Neuroblastoma/genética , Neuroblastoma/virologia , Animais , Humanos , Neuroblastoma/terapia , Ratos , Células Tumorais CultivadasRESUMO
Utilizing the technique of differential display of mRNA, we have identified p53-responsive genes that are transcriptionally up- or down-regulated as cells enter growth arrest. One gene that was down-regulated, pong16, was found to be identical to stathmin/Op18, a protein involved in the regulation of microtubule dynamics. Evidence that p53 is directly or indirectly involved in negative regulation of stathmin/Op18 expression includes the following: (i) p53-mediated growth inhibition is associated with repression of stathmin/Op18 expression following serum stimulation, (ii) reporter gene assays revealed p53-mediated repression of stathmin/Op18 promoter activity and (iii) constitutive over-expression of stathmin/Op18 bypasses a p53-mediated G(2)/M arrest in the cell cycle. These results suggest that p53-mediated negative regulation of stathmin/Op18 plays an important role in cell-cycle control.
Assuntos
Fase G2/fisiologia , Regulação da Expressão Gênica , Proteínas dos Microtúbulos , Mitose/fisiologia , Fosfoproteínas/genética , Proteína Supressora de Tumor p53/fisiologia , Regulação para Baixo , Humanos , Fosfoproteínas/biossíntese , Regiões Promotoras Genéticas/fisiologia , RNA Mensageiro/biossíntese , Estatmina , Células Tumorais CultivadasRESUMO
The tumor suppressor protein p53 is aberrantly localized to the cytoplasm of neuroblastoma cells, compromising the suppressor function of this protein. Such tumors are experimentally induced in transgenic mice expressing the large tumor (T) antigen of polyomaviruses. The oncogenic mechanisms of T antigen include complex formation with, and inactivation of, the tumor suppressor protein p53. Samples from 18 human neuroblastomas and five normal human adrenal glands were examined. BK virus DNA was detected in all neuroblastomas and none of five normal adrenal glands by PCR. Using DNA in situ hybridization, polyomaviral DNA was found in the tumor cells of 17 of 18 neuroblastomas, but in none of five adrenal medullas. Expression of the large T antigen was detected in the tumor cells of 16 of 18 neuroblastomas, but in none of the five adrenal medullas. By double immunostaining BK virus T antigen and p53 was colocalized to the cytoplasm of the tumor cells. Immunoprecipitation revealed binding between the two proteins. The presence and expression of BK virus in neuroblastomas, but not in normal adrenal medulla, and colocalization and binding to p53, suggest that this virus may play a contributory role in the development of this neoplasm.