Cutaneous Papillomavirus E6 Proteins Must Interact with p300 and Block p53-Mediated Apoptosis for Cellular Immortalization and Tumorigenesis

Abstract

The binding of the papillomavirus E6 protein to E6AP and the induction of p53 degradation are common features of high-risk genital human papillomaviruses (HPV); cutaneous HPVs, on the other hand, lack these capacities. Nevertheless, several cutaneous HPV types of the β-genus, such as HPV38 are associated with tumor formation when combined with genetic predisposition, immunosuppression, or UV exposure. In an animal model system, the cottontail rabbit papillomavirus (CRPV) rapidly induces skin cancer without additional cofactors, and CRPVE6 and E7 immortalize rabbit keratinocytes in vitro. However, CRPVE6 neither interacts with E6AP and p53 nor does it induce p53 degradation. In this study, we show that the interaction of CRPVE6, or HPV38E6, with the histone acetyltransferase p300 is crucial to inhibit the ability of p53 to induce apoptosis. Strikingly, E6 mutants deficient for p300 binding are incapable of preventing p53 acetylation, p53-dependent transcription, and apoptosis induction. Moreover, E6 mutants deficient for p300 binding cannot contribute to HPV38-induced immortalization of human keratinocytes or CRPV-induced tumor formation. Our findings highlight changes in the p53 acetylation status mediated by the viral E6 protein as a crucial requirement in the ability of high-risk cutaneous papillomaviruses to immortalize primary keratinocytes and induce tumors.

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

“…Finally, various publications have reported the interaction of E6 with the acetyltransferases p300 and CBP (23,44,49,71,72). Our comprehensive analysis showed that among the genus alpha E6 proteins, HPV16 E6 is unique in its ability to bind to both CBP and p300 ( Fig.…”

“…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).…”

Oncoprotein E7 from Beta Human Papillomavirus 38 Induces Formation of an Inhibitory Complex for a Subset of p53-Regulated Promoters

“…Mucosal high-risk HPV types induce p53 degradation via the E6 oncoprotein. Although HPV49 has the same mechanism as the mucosal high-risk human papillomavirus types in inactivating p53 (31), other beta HPV types target this cellular tumor suppressor by alternative strategies (3,7,9,14). We previously showed that the expression of HPV38 E6 and E7 oncoproteins in primary keratinocytes promoted accumulation of the p53 antagonist ⌬Np73␣ and cellular immortalization (3,4,6,14).…”

“…Beta HPV types were originally isolated in patients suffering from a rare autosomal recessive cancer-prone genetic disorder, epidermodysplasia verruciformis (EV) and are consistently detected in nonmelanoma skin cancers from EV patients and immunocompromised and normal individuals (2). Many independent studies have demonstrated that the E6 and E7 proteins of several HPV types display transforming activities in in vitro and in vivo experimental models (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). We previously showed that E6 and E7 of beta HPV38 are able to efficiently immortalize primary human keratinocytes (4,6).…”

Distinct Functions of Epidermal and Myeloid-Derived VEGF-A in Skin Tumorigenesis Mediated by HPV8

“…The E6 proteins of several beta papillomavirus types, including HPV5 and 8, target the proapoptotic protein Bak for degradation and thus prevent UV-induced apoptosis (9). They furthermore bind to p300, resulting in inhibition of p53-induced apoptosis (10), reduction of ATR mRNA and protein levels, and finally delayed repair of UV-damaged DNA (11). These activities may result in chromosomal instability particularly in the context of sun exposure and may eventually contribute to cancer development.…”