REVIEW Scarth et al., Journal of General Virology DOI 10.1099/jgv.0.001540 OPEN ACCESS The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation James A. Scarth1,2,*, Molly R. Patterson1,2, Ethan L. Morgan1,2† and Andrew Macdonald1,2,* Abstract Persistent infection with high- risk human papillomaviruses (HR- HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell- cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR- HPV oncoproteins can lead to the acquisition of host genetic mutations, eventu- ally culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis. INTRODUCTION genome of approximately 8 kb in length [1]. To date, over 400 isolates from a wide variety of fish, reptiles, birds and Papillomaviruses are small non- enveloped icosahedral mammals have been reported in the Papillomaviridae family, viruses, possessing a circular double- stranded DNA (dsDNA) over 200 of which infect humans [2, 3]. Received 17 September 2020; Accepted 25 November 2020; Published 11 January 2021 Author affiliations: 1School of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK; 2Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK. *Correspondence: James A. Scarth, bsjasc@ leeds. ac. uk; Andrew Macdonald, a. macdonald@ leeds. ac. uk Keywords: cancer; HPV; keratinocyte; oncoprotein; signalling. Abbreviations: anti- PD- L1, anti- programmed death- ligand 1; ATM, ataxia- telangiectasia mutated; ATR, ataxia- telangiectasia and Rad3- related; BAK, Bcl-2 homologous antagonist/killer; BPV, bovine papillomavirus; CARM1, coactivator associated arginine methyltransferase 1; CBP, CREB- binding protein; CCEPR, cervical carcinoma expressed PCNA regulatory; circRNA, circular RNA; CR, conserved region; DANCR, differentiation antagonizing non- protein coding RNA; DAPK1, death associated protein kinase 1; DDR, DNA damage response; DISC, death- induced signalling complex; DLG1, discs large homologue 1; DREAM, dimerization partner, pRb- like, E2F and multi- vulval class B; dsDNA, double- stranded DNA; DVL2, dishevelled 2; E, early; E6- AP, E6- associated protein; EGFR, epidermal growth factor receptor; E5KO, E5 knock out; EMT, epithelial- mesenchymal transition; ERK1/2, extracellular signal- regulated kinase 1/2; FADD, Fas- associated protein with death domain; FAM83H- AS1, FAM83H antisense RNA 1; FOXM1, forkhead box protein M1; GLUT1, glucose transporter 1; GSK3β, glycogen synthase kinase 3 beta; HAT, histone acetyltransferase; HDAC, histone deacetylase; HNSCC, head and neck squamous cell carcinoma; HOTAIR, HOX transcript antisense intergenic RNA; HPV+, HPV- positive; HPV, human papillomavirus; HR- HPV, high- risk human papillomavirus; HSPG, heparin sulphate proteoglycan; hTERT, human telomerase reverse transcriptase; IFN, interferon; IGF1R, insulin- like growth factor receptor; IL-6, interleukin-6; IL- 18BP, interleukin-18 binding protein; INSR, insulin receptor; IRF, IFN regulatory factor; ISG, interferon- stimulated gene; JAK, Janus kinase; JNK1/2, c- Jun N- terminal kinase 1/2; K14, keratin-14; L, late; lncRNA, long non- coding RNA; MALAT1, metastasis associated lung adenocarcinoma transcript 1; MAML1, mastermind- like protein 1; MAPK, mitogen- activated protein kinase; MDM2, mouse double minute 2 homologue; MHC, major histocompatibility complex; miRNA, micro RNA; mTORC1, mammalian target of rapamycin complex 1; MZF1, myeloid zinc finger 1; ncRNA, non-coding RNA; NES, nuclear export signal; NHERF1, Na+/H+ exchange regulatory factor 1; NICD, Notch intracellular domain; NKX2-1, NK2 homeobox 1; NLS, nuclear localization signal; ori, origin of DNA replication; PAE, early polyadenylation site; PAL, late polyadenylation site; PBM, PDZ- binding motif; PcG, polycomb group; PDGFR, platelet- derived growth factor receptor; PDZ, PSD-95/DLG/ZO-1; PI3K, phosphatidylinositol 3- kinase; PIP2, phosphatidylinositol 4,5- bisphosphate; PIP3, phosphatidylinositol 3,4,5- trisphosphate; PKC, protein kinase C; pRb, retinoblastoma protein; PRC2, Polycomb repressive complex 2; PRMT1, protein arginine methyltransferase 1; PRR, pattern recognition receptor; PTEN, phosphatase and tensin homologue; ROS, reactive oxygen species; RTK, receptor tyrosine kinase; SIAH1, seven in absentia homologue 1; SNX27, sorting nexin 27; Sp1, specificity protein 1; STAT, signal transducer and activator of transcription; STK4, serine/threonine- protein kinase 4; SV40, simian virus 40; TAZ, transcriptional coactivator with PDZ- binding motif; TEAD, TEA domain; TGN, trans- Golgi network; TINCR, tissue differentiation- inducing non- protein coding RNA; TLR9, Toll- like receptor 9; TMD, transmembrane domain; TMPOP2, thymopoietin pseudogene 2; TNFR1, tumour necrosis factor receptor 1; TRAIL, TNF- related apoptosis- inducing ligand; TSC1/2, tuberous sclerosis complexes 1/2; TYK2, non- receptor tyrosine kinase 2; URR, upstream regulatory region; USF1, upstream stimulating factor 1; USF2, upstream stimulating factor 2; UV, ultraviolet; v- ATPase, vacuolar H+- ATPase; YAP1, yes- associated protein 1. †Present address: Tumour Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institute of Health, Bethesda, MD 20892, USA. 001540 © 2021 The Authors This is an open- access article distributed under the terms of the Creative Commons Attribution License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution. 1 Scarth et al., Journal of General Virology 2021 The study of human papillomaviruses (HPVs) has largely HUMAN PAPILLOMAVIRUSES been driven by the severity of HPV-associated pathologies: HPV genome organization whilst the HPVs that infect the cutaneous epithelium and typically result in benign wart or verruca formation, as The HPV genome is organized into three functional sections: well as the low- risk mucosal HPV types 6 and 11 associ- the early (E) region, the late (L) region, and an upstream regu- ated with genital warts, have received some attention, the latory region (URR) (Fig. 1a) [8]. Together, the early and late greatest focus has been on the high- risk HPVs (HR- HPVs) regions consist of nine ORFs, six in the early region (E1, E2, associated with the development of cancer [1, 4]. This link E1^E4, E5, E6, E7 and E8) and two in the late region (L1 between HPV infection and cancer was first established over and L2), whilst the URR contains the origin of DNA repli- 35 years ago when HPV16 DNA was found to be present in cation (ori) as well as the transcription-factor binding sites a large proportion of cervical cancer biopsies [5]. However, required for the regulation of RNA- polymerase- II- dependent it is important to consider that the majority of HR-HPV transcription. The three regions are separated by early and infections will not progress to cancer; indeed 85 % of cases late polyadenylation sites (PAE and PAL, respectively). The are subclinical transient infections [6]. There are currently HPV genome contains two major promoters: p97 in HPV16 15 recognized HR- HPV types: HPV16, 18, 31, 33, 35, 39, and 31 (p105 in HPV18) is responsible for expression of the 45, 51, 52, 56, 58, 59, 68, 73, 82 [7]. Together, HR- HPVs are early genes and lies upstream of the E6 ORF, and p670 in responsible for >99.7 % of cervical cancer cases, of which HPV16 (p811 in HPV18 and p742 in HPV31) is responsible 55 % are HPV16- positive and 15 % are HPV18- positive, for differentiation- dependent late gene expression and lies along with a growing number or oropharyngeal cancers [8]. within the E7 ORF [25–27]. Although there are multiple Cancer of the cervix is the fourth most common malignancy minor promoters, their functions are poorly characterized in women worldwide and the fourth leading cause of cancer- [27]. Importantly, the HR-HPV E6 and E7 oncoproteins are related deaths in women: in 2018, around 570 000 people encoded by a single bicistronic mRNA transcript with splicing were diagnosed with cervical cancer and over 300 000 deaths allowing for the expression of each ORF [27]. worldwide could be attributed to the disease [9]. Further- more, HR- HPV infection is associated with cancers at a HPV life cycle variety of other anogenital sites: around 50% of penile, 25 % The life cycle of HPV is intrinsically linked to the epithelial of vulvar, 80 % of vaginal and close to 90 % of anal cancers differentiation programme. For an infection to be established, are HPV- driven [10]. virions must gain access to the basal lamina of the strati- fied epithelium via microlesions or by entering cells at the Although their expression is insufficient for progression to squamo- columnar junction [1, 28]. Primary attachment of cancer, the main drivers