Human Papillomavirus Type 8 E6 Oncoprotein Inhibits Transcription of the PDZ Protein Syntenin-2

Abstract

cThe E6 proteins from high-risk alpha human papillomavirus (HPV) types (e.g., HPV16) are characterized by the presence of a PDZ-binding motif through which they interact with a number of cellular PDZ domain-containing substrates and cooperate in their degradation. The ability of these E6 proteins to bind to PDZ domain proteins correlates with the oncogenic potential of the virus. The E6 proteins of oncogenic HPV from the genus Betapapillomavirus (betaPV, e.g., HPV8) do not encode a PDZ-binding motif. We found that the PDZ domain protein syntenin-2 is transcriptionally downregulated in primary human epidermal keratinocytes (PHEK) by HPV8 E6. The mRNA levels of the known HPV16 E6 PDZ protein targets Dlg, Scribble, Magi-1, Magi-3, PSD95, and Mupp1 were not changed by HPV8 E6. Decreased protein levels of syntenin-2 were observed in cell extracts from PHEK expressing HPV5, -8, -16, -20, and -38 E6 but not in HPV1 and -4 E6-positive keratinocytes. Surprisingly, HPV16 E6 also repressed transcription of syntenin-2 but with a much lower efficiency than HPV8 E6. In healthy human skin, syntenin-2 expression is localized in suprabasal epidermal layers. In organotypic skin cultures, the differentiation-dependent expression of syntenin-2 was absent in HPV8 E6-and E6E7-expressing cells. In basal cell carcinomas of the skin, syntenin-2 was not detectable, whereas in squamous cell carcinomas, expression was located in differentiated areas. Short hairpin RNA-mediated knockdown of syntenin-2 led to an inhibition of differentiation and an increase in the proliferation capacity in PHEK. These results identified syntenin-2 as the first PDZ domain protein controlled by HPV8 and HPV16 at the mRNA level. Human papillomaviruses (HPV) are associated with epithelial cancers of the genital tract, and high-risk HPV of the genus Alphapapillomavirus (alphaPV) have been proven to be a necessary causative factor in the development of cervical cancer (42). HPV types of the genus Betapapillomavirus (betaPV) have been implicated in the development of cutaneous tumors, especially squamous cell carcinomas (SCC) and actinic keratoses (AK) as their precursor lesions (13). The first evidence implicating cutaneous HPV types in the pathogenesis of cutaneous SCC was based on the detection of betaPV types, predominantly HPV5 or HPV8 and rarely HPV type 14, 17, 19, 20, 24, or 47, in SCC of epidermodysplasia verruciformis (EV) patients (11,15,27,29). Also, in non-EV patients, betaPV are frequently detected in cutaneous SCC and AK. Interestingly, the high prevalence and viral load of betaPV types in actinic keratoses (30, 38) and the decrease of viral load during skin carcinogenesis may point to a particular involvement of HPV in the early stages of skin cancer development. UV radiation is recognized as the main risk factor in SCC development (28), and HPV is discussed as a cofactor in concert with UV radiation (7,16,18,21,33,35,37). However, the role of betaPV and their cell-transforming mechanisms are still less clear than those of high-risk alphaPV (4).The ...

Cutaneous alpha, beta and gamma human papillomaviruses in relation to squamous cell carcinoma of the skin: A population‐based study

“…[43][44][45] E6 also may disrupt cell adhesion and growth factor signaling pathways, and induce secretion of anti-apoptotic factors to inhibit UV-induced apoptosis. 46,47 Additional work suggests beta HPV may act transiently, evidenced by loss of HPV protein expression with cancer progression, contributing to the initiating events of carcinogenesis, and allowing the HPV infection to persist by suppressing the local immune response. 48,49 While further work is needed to fully understand these mechanisms, an early role in carcinogenesis may be one explanation for the limited number of studies that have been able to relate beta HPV seropositivity to beta HPV DNA presence in SCC tumors.…”

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

“…Both the function and the nature of interactions between beta E6s and PDZ domain proteins have yet to be determined. It should be noted that interactions with proteins containing PDZ domains are not restricted to oncogenic viruses, that these interactions may contribute important functions to the replication of viruses even in the absence of a tumorigenic function (29), and also that HPV8 E6 was recently shown to inhibit expression of the PDZ protein Syntenin 2 at the level of transcription (36).…”

Human papillomavirus type 8 oncoproteins E6 and E7 cooperate in downregulation of the cellular checkpoint kinase‐1

“…39 The blots were probed with antibodies targeting CHK1 (clone G-4, sc-8408, Santa Cruz, Heidelberg, Germany) or mono-and polyubiquitinylated conjugates (clone FK2H, PW0150, Enzo Life Sciences GmbH, Lörrach, Germany). 39 The blots were probed with antibodies targeting CHK1 (clone G-4, sc-8408, Santa Cruz, Heidelberg, Germany) or mono-and polyubiquitinylated conjugates (clone FK2H, PW0150, Enzo Life Sciences GmbH, Lörrach, Germany).…”