Consequences of disruption of the interaction between p53 and the larger adenovirus early region 1B protein in adenovirus E1 transformed human cells

Abstract

The adenovirus early region 1B (Ad E1B) genes have no transforming capability of their own but markedly increase the transformation frequency of Ad E1A following co-transfection into mammalian cells. The larger E1B proteins of both Ad2/5 and Ad12 bind to p53 and inhibit its ability to transcriptionally activate other genes. We have previously demonstrated that synthetic peptides identical to the binding sites for p53 on both the Ad2 and Ad12 E1B proteins will disrupt the interaction in vivo and in vitro. In the work presented here we have examined the e ects of complex dissociation on Ad E1-transformed human cells. It has been shown, using confocal microscopy, that when the peptide identical to the p53 binding site was added to Ad5 E1-transformed cells it initally located in the cytoplasmic dense bodies where it caused disruption of the p53/E1B complex. Peptide and p53 then translocated to the nucleus. In Ad12 E1-transformed cells the peptide localized in the nucleus directly and there caused a reorganization of p53 staining from a highly organized,¯e cked' distribution to one in which nuclear staining was homogeneous and di use. Peptides added to either Ad5 E1 or Ad12 E1 transformed cells resulted in the release of transcriptionally active p53. Interestingly, the level of p53 then fell presumably as a result of proteasomal action -this was probably a re¯ection of the short halflife of`free' (i.e. dissociated) p53 compared to that of the bound protein. Free p53 did not cause apoptosis in target cells probably due to the presence of the smaller (19K) E1B proteins. However, addition of peptide leads to a signi®cant reduction in cell growth rate. We have further demonstrated that a signi®cant proportion of those cells which had taken up peptide had ceased DNA synthesis, probably due to a p53-induced cell cycle arrest. The role of the larger E1B protein during transformation is considered in view of these data. Oncogene (2000) 19, 452 ± 462.

Adenovirus type 5 early region 1B 55-kDa oncoprotein can promote cell transformation by a mechanism independent from blocking p53-activated transcription

“…In the case of Ad2/5 E1B-55K, formation of cytoplasmic aggregates typically occurs around the MTOC (Brown et al, 1994;Johnston et al, 1998;Liu et al, 2005) and is accompanied by the sequestration of a variety of E1B-55K-associated proteins such as p53, WT1 and components of the MRN complex (Maheswaran et al, 1998;Liu et al, 2005). This cytoplasmic restriction imposed upon p53 and MRN contributes to inhibition of p53-induced growth arrest and apoptosis (Hutton et al, 2000; and blocks MRN function (Liu et al, 2005). Studies in this report confirm that the cytoplasmic inclusion body in transformed BRK cells expressing wt Ad5 E1B-55K contains Mre11 and Rad50 (Figure 5), is localized at the MTOC ( Figure 4B) and may correspond to an aggresome, which, as opposed to human cells, does not trigger vimentin reorganization ( Figure 4A).…”

“…Collectively available data suggest that these activities are linked in part to p53 transcription-independent pathways (Lo¨ber et al, 2002;Hobom and Dobbelstein, 2004;Sieber and Dobner, 2007), and to the ability of Ad2/5 E1B-55K products to inactivate p53 and the tumor suppressor protein WT1 by sequestration into a cytoplasmic inclusion body (Maheswaran et al, 1998;Grand et al, 1999;Hutton et al, 2000; typically situated around the microtubule organizing center (MTOC) (Brown et al, 1994). The cytoplasmic restriction imposed upon p53 requires binding of Ad2/5 E1B-55K to p53, but is independent of CRM1-mediated nuclear export of the viral protein in transformed rat cells (Endter et al, 2005).…”

Functional identification of LZTS1 as a candidate prostate tumor suppressor gene on human chromosome 8p22

“…In the adenovirustransformed HEK-293 cell line, E1B inhibits p53 activity by complex formation. Disruption of the p53/ E1B complexes releases active p53, which induces cell cycle arrest (Hutton et al, 2000). Thus, it is conceivable that ectopic expression of LZTS1 in HEK-293 cells could disrupt the sequestration of p53 by E1B and lead to growth arrest and/or apoptosis.…”

SUMO-1 modification required for transformation by adenovirus type 5 early region 1B 55-kDa oncoprotein

“…During the past few years it has been well established that the transforming potential of E1B-55kDa correlates with its ability to act as a direct transcriptional repressor targeted to p53-responsive promoters by binding to the tumor suppressor protein (3,4). Considerable evidence suggests that these activities antagonize p53-induced apoptosis (5) and͞or cell cycle arrest (6). The regions required for transformation map to several segments in the Ad protein, including the p53-binding domains located around amino acid position 180 (Fig.…”