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

Abstract

Beta-human papillomaviruses (b-HPV) infect cutaneous epithelia, and accumulating evidence suggests that the virus may act as a co-factor with UV-induced DNA damage in the development and progression of non-melanoma skin cancer, although the molecular mechanisms involved are poorly understood. The E6 protein of cutaneous b-HPV types encodes functions consistent with a role in tumorigenesis, and E6 expression can result in papilloma formation in transgenic animals. The E6 proteins of high-risk a-HPV types, which are associated with the development of anogenital cancers, have a conserved 4 aa motif at their extreme C terminus that binds to specific PDZ domain-containing proteins to promote cell invasion. Likewise, the high-risk b-HPVs HPV5 and HPV8 E6 proteins also share a conserved C-terminal motif, but this is markedly different from that of a-HPV types, implying functional differences. Using binding and functional studies, we have shown that b-HPV E6 proteins target b 1 -integrin using this C-terminal motif. E6 expression reduced membrane localization of b 1 -integrin, but increased overall levels of b 1 -integrin protein and its downstream effector focal adhesion kinase in human keratinocytes. Altered b 1 -integrin localization due to E6 expression was associated with actin cytoskeleton rearrangement and increased cell migration that was abolished by point mutations in the C-terminal motif of E6. We concluded that modulation of b 1 -integrin signalling by E6 proteins may contribute towards the pathogenicity of these b-HPV types. INTRODUCTIONUV-induced damage to keratinocytes is the main aetiological factor in the development of non-melanoma skin cancer (NMSC). Keratinocytes are the host cells of human papillomavirus (HPV) infection and the HPV life cycle is tightly coupled to the keratinocyte differentiation programme. HPVs encode genes that promote keratinocyte survival and proliferation after UV exposure and uncouple cell-cycle exit from differentiation (Hudson et al., 1990;Jones et al., 1997). Infection with high-risk b-HPVs is associated with the development of NMSC, the most commonly diagnosed cancer in Caucasians (Diepgen & Mahler, 2002;Kiviat, 1999). HPVs of the genus Betapapillomavirus (formerly known as Epidermodysplasia verruciformis or EV types) exhibit cutaneous tropism where EV individuals are prone to infection with these viral types. EV individuals have a propensity to develop NMSC at sunexposed body sites as early as the age of 20 years (Gül et al., 2007), where infection with the b1-HPV types 5 and 8 are associated with the highest risk of malignancy (Orth, 1986;Pfister, 2003;Pfister & Ter Schegget, 1997). In more recent epidemiological studies, a high percentage of squamous cell carcinoma (SCC) isolated from immunocompromised organ transplant recipients was found to contain b-HPV DNA (Harwood et al., , 2004Proby et al., 2011;Weissenborn et al., 2012) and the immunocompromised population has a 200-fold increased risk of SCC formation compared with the immunocompetent population (Hartevelt et a...

Characterization of novel human papillomavirus types 157, 158 and 205 from healthy skin and recombination analysis in genus γ-Papillomavirus

“…A specific characteristic of the oncogenic mucosal HPV types is a PDZ-binding motif on the carboxyl terminus of E6, which is important in cell proliferation, cell polarity and cell transformation (Cavatorta et al, 2004). Although the PDZbinding domains were not found at the carboxyl terminus of the novel γ-PV types here described, it has been shown that the E6 proteins of some oncogenic β-PV types encode a conserved domain (YXDM) at the carboxyl terminus which alters the localization and signalling of the β1-integrin that was associated with increased cell migration, and therefore with a higher pathogenicity of these β-HPV types (Holloway and Storey, 2014). Binding partners and possible functions of the different conserved C-terminal motifs of the E6 proteins should be explored in order to investigate the pathological mechanism of some γ-PV types.…”

Comprehensive pan-carcinoma analysis of ITGB1 distortion and its potential clinical significance for cancer immunity

“…Hpv-positive NPC tends to have a poor prognosis [ 42 ]. It has been shown that the conserved C-terminal sequence of the E6 protein of high-risk cutaneous β-HPV promotes cell migration by altering β1-integrin localization and signaling, which may be involved in contributing to the pathogenicity of these β-HPV types [ 43 ].…”

The Role of β1 Integrin/CD29 as a Potential Prognostic Factor for the Risk of Progression to Cervical Carcinoma in HPV-Associated Lesions

“…Ultrastructural studies show integrin chains’ distribution in the basal cell layer of the squamous epithelium, which is crucial for the interaction between the epithelium and basal lamina [ 20 ]. The interactions between them can be altered during the first steps of dysplastic transformations that come before micro-invasive cervical cancer [ 21 , 22 , 23 ].…”