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 downregulates 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.p53 is a key regulator of cell growth and apoptosis. Its central role in tumor suppression becomes evident by the fact that the p53 gene is mutated in about 50% of human malignancies. p53 acts as a transcription factor, modulating the expression of growth and death regulators. As a result, cell proliferation is suppressed, and/or programmed cell death is induced (1). It is generally accepted that p53 activates a number of promoters through direct interaction with the promoter DNA and the subsequent recruitment of the basal transcription machinery, e.g. the TFIID complex and the p300/CPB histone acetyl transferases. A tetramer of p53 molecules is assembled through the carboxyl-terminal oligomerization domains. This allows the central domains to interact directly with a consensus DNA element. As a consequence, the amino-terminal transactivation domains interact with basal transcription factors,

The Marburg virus (MBGV) nucleocapsid complex is composed of four viral proteins (NP, L, VP35, and VP30) and the negative-strand nonsegmented genomic RNA. NP, L, and VP35 are functionally conserved among the order Mononegavirales, whereas VP30, a phosphoprotein, represents a filovirus-specific nucleocapsid protein. In the present paper, we have characterized the localization and function of VP30 phosphorylation. The main phosphorylation sites are represented by seven serine residues in the region of amino acid 40 to 51 of VP30. Additionally, trace amounts of phosphothreonine were detected. Substitution of serine residues 40 and 42 by alanine abolished the interaction of VP30 with NP-induced inclusion bodies, which contain nucleocapsid-like structures formed by NP. Substitution of the other phosphoserine residues had little effect on this interaction. Replacement of the introduced alanine residues 40 and 42 by aspartate restored the interaction between VP30 and the NP inclusions pointing to the importance of negative charges at these particular positions.

Classical Hodgkin's lymphoma (cHL) is a distinct malignancy of the immune system. Despite the progress made in the understanding of the pathology of cHL, the transforming events remain to be elucidated. It has been proposed that mutations in the TP53 gene in biopsy material as well as cell lines derived from cHL are rare and therefore not notably involved in the pathogenesis of the malignant H&RS cells. Re-evaluating the expression in cHL-derived cell lines, we found that in 3/6 of these cell lines, TP53 transcripts are characterized by deletions within exon 4 (L428 cells) and nearly a complete loss of exons 10 - 11 (L1236) or exons 8 - 11 (HDLM-2), respectively. These changes were found in otherwise rarely mutated regions of TP53. Cell lines L1236 and HDLM-2 harbour fusions with alu-repeats in their TP53 mRNA 3'-ends, resulting in the carboxyterminal truncation and loss of the transcriptional activity of p53. Transcriptional inactivity was also found for p53 in L428 cells. This study characterizes mutations in TP53 transcripts within cHL cell lines with associated functional defects in the resulting p53 proteins and therefore reintroduces the concept that mutations of TP53 might be involved in the pathogenesis of Hodgkin's lymphoma.

Adenoviruses are an extensively studied system for modeling oncogenesis and for experimental cancer therapy. The most commonly analyzed virus types are 2 and 5, and little distinction has been made between them in past studies. Adenoviruses used for therapeutic purposes are frequently hybrids between these types, including the prototype dl1520/Onyx015. We tested the replication of the wild-type viruses WtD (a hybrid of the type 2 E1 region and type 5) and dl309 (type 5) in comparison with the mutants dl1520 (hybrid) and dl338 (type 5), the latter two lacking part of the E1B-55 kDa coding region. We found that the hybrid viruses replicated with considerably lower efficiency than their type 5 counterparts in H1299 cells (dl309:WtD = 3-4, dl338:dl1520 > 10). Moreover, adenovirus type 2 E1A expression from the hybrid viruses was strongly reduced in comparison to adenovirus type 5 E1A, as revealed by immunoblot analysis and RT-PCR, providing a potential explanation for the differences in virus yield. Differential E1A expression levels need to be taken into account for the construction of effective therapeutic viruses and when studying viral transformation.