Skin human papillomavirus type 38 alters p53 functions by accumulation of ΔNp73

Abstract

The E6 and E7 of the cutaneous human papillomavirus (HPV) type 38 immortalize primary human keratinocytes, an event normally associated with the inactivation of pathways controlled by the tumour suppressor p53. Here, we show for the first time that HPV38 alters p53 functions. Expression of HPV38 E6 and E7 in human keratinocytes or in the skin of transgenic mice induces stabilization of wild-type p53. This selectively activates the transcription of DNp73, an isoform of the p53-related protein p73, which in turn inhibits the capacity of p53 to induce the transcription of genes involved in growth suppression and apoptosis. DNp73 downregulation by an antisense oligonucleotide leads to transcriptional re-activation of p53-regulated genes and apoptosis. Our findings illustrate a novel mechanism of the alteration of p53 function that is mediated by a cutaneous HPV type and support the role of HPV38 and DNp73 in human carcinogenesis.

Loss of p53 or p73 in human papillomavirus type 38 E6 and E7 transgenic mice partially restores the UV-activated cell cycle checkpoints

“…We therefore determined whether similar events occurred in the mouse model. DNp73 expression levels were analysed by reverse transcriptase-PCR in HPV38 E6/E7 Tg mice in the presence or absence of p53 as previously described (Accardi et al, 2006). In agreement with the in vitro data, we observed that p53 À/À HPV38 E6/E7 Tg mice did not express DNp73 (Figure 1a).…”

“…Since downregulation of DNp73 by antisense oligonucleotide in HPV38 E6/E7 keratinocytes led to a restoration of p53 transcriptional functions (Accardi et al, 2006), we next determined whether similar events can occur in HPV38 E6/E7 Tg mice lacking DNp73. HPV38 E6/E7 Tg mice were crossed with p73 À/À mice, which were previously generated by replacing the exons 5 and 6, leading to deficiency of all p73 isoforms (Yang et al, 2000).…”

“…In fact, while HPV16 E6 induces p53 degradation via the proteasome pathway (zur Hausen, 2002), HPV38 E6 and E7 promote the accumulation of a specific p53 form that selectively activates the transcription of DNp73, which in turn inhibits p53 ability to induce the transcription of genes involved in growth suppression and apoptosis (Accardi et al, 2006). The accumulation of p53 and DNp73 was also detected in keratinocytes of transgenic (Tg) mice expressing HPV38 E6 and E7 under the control of keratin-10 promoter (Accardi et al, 2006). In addition, in contrast to normal mice, HPV38 E6/E7 Tg mice do not respond to ultraviolet (UV) irradiation.…”

“…Characterization of the biological properties of the products of the early genes E6 and E7 from different beta HPV types in in vitro and in vivo model has highlighted the potential carcinogenicity of these viruses (Jackson et al, 2000;Caldeira et al, 2003;Akgul et al, 2005;Dong et al, 2005;Schaper et al, 2005;Accardi et al, 2006;Michel et al, 2006). We showed that expression of E6 and E7 from the beta HPV38 in primary human keratinocytes results in inactivation of the tumour suppressor p53 and pRb and immortalization (Caldeira et al, 2003;Accardi et al, 2006). Interestingly, HPV38 inactivates p53 functions by a mechanism that differs from the one used by the mucosal high-risk HPV16.…”

“…To evaluate this hypothesis, we have crossed HPV38 E6/E7 Tg mice with p53 null mice (Donehower et al, 1992). Identification of the different Tg lines was achieved by extracting DNA from the tails of 5-week-old mice followed by PCR with specific primers for the K10 HPV38 E6 and E7 region and p53 In vitro experiments in primary human keratinocytes showed that p53 gene silencing by small interfering RNA abolished DNp73 transcription activation (Accardi et al, 2006). We therefore determined whether similar events occurred in the mouse model.…”