HPV-16 E7 Interacts with the Endocytic Machinery via the AP2 Adaptor μ2 Subunit

The HPV101 E7 protein shares host cellular targets and biological activities with high-risk HPV16 E7

Human papillomaviruses (HPVs) are a diverse family of viruses with over 450 members that have been identified and fully sequenced. They are classified into five phylogenetic genera: alpha, beta, gamma, mu, and nu. The high-risk alpha HPVs, such as HPV16, have been studied the most extensively due to their medical significance as cancer-causing agents. However, while nearly 70% of all HPVs are members of the gamma genus, they are almost entirely unstudied. This is because gamma HPVs have been considered medically irrelevant commensals as most of them infect the skin and are not known to cause significant clinical lesions in immunocompetent individuals. Members of the gamma 6 HPVs, however, have been detected in the anogenital tract mucosa and HPV101 has been isolated from a premalignant cervical lesion. Moreover, gamma 6 HPVs have a unique genome structure. They lack E6 proteins but in place of E6, they encode unique, small hydrophobic proteins without any close viral or cellular homologs that have been termed E10. Here, we report that HPV101 E7 shares biochemical activities with the high-risk alpha HPV16 E7, including the ability to target the pRB and PTPN14 tumor suppressors for degradation. This study underscores the importance of further characterizing HPV101 and other unstudied HPV species.

The effect of phosphorylation efficiency on the oncogenic properties of the protein E7 from high-risk HPV

The Human papillomavirus (HPV) causes tumors in part by hijacking the host cell cycle and forcing uncontrolled cellular division. While there are >200 genotypes of HPV, 15 are classified as high-risk and have been shown to transform infected cells and contribute to tumor formation. The remaining low-risk genotypes are not considered oncogenic and result in benign skin lesions. In high-risk HPV, the oncoprotein E7 contributes to the dysregulation of cell cycle regulatory mechanisms. High-risk E7 is phosphorylated in cells at two conserved serine residues by Casein Kinase 2 (CK2) and this phosphorylation event increases binding affinity for cellular proteins such as the tumor suppressor retinoblastoma (pRb). While low-risk E7 possesses similar serine residues, it is phosphorylated to a lesser degree in cells and has decreased binding capabilities. When E7 binding affinity is decreased, it is less able to facilitate complex interactions between proteins and therefore has less capability to dysregulate the cell cycle. By comparing E7 protein sequences from both low- and high-risk HPV variants and using site-directed mutagenesis combined with NMR spectroscopy and cell-based assays, we demonstrate that the presence of two key nonpolar valine residues within the CK2 recognition sequence, present in low-risk E7, reduces serine phosphorylation efficiency relative to high-risk E7. This results in significant loss of the ability of E7 to degrade the retinoblastoma tumor suppressor protein, thus also reducing the ability of E7 to increase cellular proliferation and reduce senescence. This provides additional insight into the differential E7-mediated outcomes when cells are infected with high-risk verses low-risk HPV. Understanding these oncogenic differences may be important to developing targeted treatment options for HPV-induced cancers.

A safe and potentiated multi-type HPV L2-E7 nanoparticle vaccine with combined prophylactic and therapeutic activity

Persistent infection with high-risk human papillomavirus (HPV) is widely recognized as the primary cause of cervical and other malignant cancers. There are six licensed prophylactic vaccines available against HPV, but none of them shows any significant therapeutic effect on pre-existing infections or lesions. Thus, a prophylactic vaccine also endowed with therapeutic activity would afford protection regardless of the vaccine recipients HPV-infection status. Here, we describe the refinement and further potentiation of a dual-purpose HPV nanoparticle vaccine (hereafter referred to as cPANHPVAX) relying on eight different HPV L2 peptide epitopes and on the E7 oncoantigens from HPV16 and 18. cPANHPVAX not only induces anti-HPV16 E7 cytotoxic T-cell responses in C57BL/6 mice, but also anti-HPV18 E7 T-cell responses in transgenic mice with the A2.DR1 haplotype. These cytotoxic responses add up to a potent, broad-coverage humoral (HPV-neutralizing) response. cPANHPVAX safety was further improved by deletion of the pRb-binding domains of E7. Our dual-purpose vaccine holds great potential for clinical translation as an immune-treatment capable of targeting active infections as well as established HPV-related malignancies, thus benefiting both uninfected and infected individuals.

HPV16 E7 modulates the cell surface expression of MET and CD109 via the AP2 complex

Multiple cellular pathways are affected by HPV E6 and E7 oncoproteins, including endocytic and cellular trafficking. HPV-16 E7 can target the adaptor protein (AP) complex, which contains proteins important during endocytosis transport. To further investigate the role of HPV E7 during this process, we analysed the expression of cell surface proteins in NIKS cells expressing HPV-16 E7. We show that different cell surface proteins are regulated by HPV-16 E7 via interaction with AP2. We observed that the expression of MET and CD109 membrane protein seems to be upregulated in cells expressing E7. Moreover, the interaction of MET and CD109 with AP2 proteins is disrupted by HPV-16 E7. In addition, in the absence of HPV-16 E7, there is a downregulation of the cell membrane expression of MET and CD109 in HPV-positive cell lines. These results expand our knowledge of the functions of E7 and open new potential cellular pathways affected by this oncoprotein.

Role of Virus-Induced EGFR Trafficking in Proviral Functions

Since its discovery in the early 1980s, the epidermal growth factor receptor (EGFR) has emerged as a pivotal and multifaceted player in elucidating the intricate mechanisms underlying various human diseases and their associations with cell survival, proliferation, and cellular homeostasis. Recent advancements in research have underscored the profound and multifaceted role of EGFR in viral infections, highlighting its involvement in viral entry, replication, and the subversion of host immune responses. In this regard, the importance of EGFR trafficking has also been highlighted in recent studies. The dynamic relocation of EGFR to diverse intracellular organelles, including endosomes, lysosomes, mitochondria, and even the nucleus, is a central feature of its functionality in diverse contexts. This dynamic intracellular trafficking is not merely a passive process but an orchestrated symphony, facilitating EGFR involvement in various cellular pathways and interactions with viral components. Furthermore, EGFR, which is initially anchored on the plasma membrane, serves as a linchpin orchestrating viral entry processes, a crucial early step in the viral life cycle. The role of EGFR in this context is highly context-dependent and varies among viruses. Here, we present a comprehensive summary of the current state of knowledge regarding the intricate interactions between EGFR and viruses. These interactions are fundamental for successful propagation of a wide array of viral species and affect viral pathogenesis and host responses. Understanding EGFR significance in both normal cellular processes and viral infections may not only help develop innovative antiviral therapies but also provide a deeper understanding of the intricate roles of EGFR signaling in infectious diseases.

Identification and characterisation of novel potential phospho-acceptor sites in HPV-16 E7

Several studies have described functional regulation of high-risk human papillomaviruses (HPVs), E6 and E7 oncoproteins via posttranslational modifications (PTMs). However, how these PTMs modulate the activity of E6 and E7, particularly in their targeting of cellular proteins, is not completely understood. In this study, we show that HPV16 E7 can be phosphorylated by casein kinase I (CKI) and glycogen synthase kinase 3 (GSK3). This principal phosphorylation occurs at threonine residues 5 and 7 with a more minor role for residues 19-20 in the N-terminal region of 16 E7. Intriguingly, whilst mutational analyses suggest that residues 5 and 7 may be dispensable for the transformation of primary baby rat kidney cells by E7, intact residues 19 and 20 are required. Furthermore, negative charges at these residues (TT19-20DD) enhance the pRb-E7 interaction and cells display increased proliferation and invasion capacities. Using a proteomic approach with a phosphorylated peptide spanning the TT19-20 region of HPV16 E7, we have identified a panel of new, phospho-specific E7 interacting partners. These results shed new light on the complexity of N-terminal phosphorylation of E7 and how this can contribute towards expanding the repertoire of E7 targeted pathways.