Beta-HPV 5 and 8 E6 Promote p300 Degradation by Blocking AKT/p300 Association

Abstract

The E6 oncoprotein from high-risk genus alpha human papillomaviruses (α-HPVs), such as HPV 16, has been well characterized with respect to the host-cell proteins it interacts with and corresponding signaling pathways that are disrupted due to these interactions. Less is known regarding the interacting partners of E6 from the genus beta papillomaviruses (β-HPVs); however, it is generally thought that β-HPV E6 proteins do not interact with many of the proteins known to bind to α-HPV E6. Here we identify p300 as a protein that interacts directly with E6 from both α- and β-HPV types. Importantly, this association appears much stronger with β-HPV types 5 and 8-E6 than with α-HPV type 16-E6 or β-HPV type 38-E6. We demonstrate that the enhanced association between 5/8-E6 and p300 leads to p300 degradation in a proteasomal-dependent but E6AP-independent manner. Rather, 5/8-E6 inhibit the association of AKT with p300, an event necessary to ensure p300 stability within the cell. Finally, we demonstrate that the decreased p300 protein levels concomitantly affect downstream signaling events, such as the expression of differentiation markers K1, K10 and Involucrin. Together, these results demonstrate a unique way in which β-HPV E6 proteins are able to affect host-cell signaling in a manner distinct from that of the α-HPVs.

Comprehensive Analysis of Host Cellular Interactions with Human Papillomavirus E6 Proteins Identifies New E6 Binding Partners and Reflects Viral Diversity

“…The downstream effects of the 16E6-p300/CBP interaction have been proposed to include inhibition of p53 and NF-B transcription and an ultimate inhibition of cellular differentiation (49) and a downregulation of p53 activity and p53-dependent transcription (61,71). These functions are in contrast to the proposed effects of p300 binding to HPV5 and -8 E6s, which are the degradation of p300 and the altered expression of cellular differentiation markers resulting from E6 blocking the association of Akt with p300 (23).…”

“…E6s from HPV type 16 (HPV16), -18, -11, -5, -8, and -38 as well as those from cottontail rabbit papillomavirus (CRPV) and bovine papillomavirus type 1 (BPV1) have been reported to bind to the acetyltransferases CBP and/or p300, although this has this been demonstrated convincingly only for HPV16, -5, and -8 E6s by a coimmunoprecipitation of endogenous p300 from E6-expressing cells (23,44,49,61,71,72). The downstream effects of the 16E6-p300/CBP interaction have been proposed to include inhibition of p53 and NF-B transcription and an ultimate inhibition of cellular differentiation (49) and a downregulation of p53 activity and p53-dependent transcription (61,71).…”

A conserved C-terminal sequence of high-risk cutaneous beta-human papillomavirus E6 proteins alters localization and signalling of β1-integrin to promote cell migration

“…2012), and recently of the HPV8 E6 protein (Howie et al, 2011). As b-HPVs do not encode the E5 protein, the findings here suggest that the b-HPV E6 proteins evolved Cutaneous HPV E6 proteins disrupt b 1 -integrin function to disrupt b 1 -integrin function through the YHDW motif, implicating modulation of b 1 -integrin function, and disruption of cell adhesion complexes, as an important activity of both b-and a-HPVs.…”

“…E6 proteins encoded by b-HPVs do not in general share this function; however, a recent report suggested that the HPV49 E6 protein is able to target p53 for degradation to some degree (Cornet et al, 2012), but whether this is dependent on the p53 isoform (Storey et al, 1998) et al, 2002). Expression of b-HPV E6 types HPV8 and -38 also prevents keratinocyte differentiation through targeting of MAML-1 in the Notch pathway (Brimer et al, 2012; Tan et al, 2012) and perturbs cell-survival signalling through disruption of the association of the transcriptional coactivator p300 with AKT, a key factor in promoting cell survival (Howie et al, 2011).…”

“…E6 proteins encoded by b-HPVs do not in general share this function; however, a recent report suggested that the HPV49 E6 protein is able to target p53 for degradation to some degree (Cornet et al, 2012), but whether this is dependent on the p53 isoform (Storey et al, 1998) et al, 2002). Expression of b-HPV E6 types HPV8 and -38 also prevents keratinocyte differentiation through targeting of MAML-1 in the Notch pathway (Brimer et al, 2012; Tan et al, 2012) and perturbs cell-survival signalling through disruption of the association of the transcriptional coactivator p300 with AKT, a key factor in promoting cell survival (Howie et al, 2011).Interestingly, the b-HPV E6 proteins also differ from those of high-risk a-HPV as b-HPV E6 proteins lack a conserved ETQV/L motif located at the extreme C terminus of the protein, as described for HPV16 and -18. The ETQV/L motif mimics a known PDZ domain-binding consensus sequence (X-T/S-X-V), and subsequently a-HPV E6 proteins use this motif to target specific PDZ domaincontaining proteins for degradation.…”