E2 Binding Sites Research Articles

Ion channel inhibition by targeted recruitment of NEDD4-2 with divalent nanobodies.

Targeted recruitment of E3 ubiquitin ligases to degrade traditionally undruggable proteins is a disruptive paradigm for developing new therapeutics. Two salient limitations are that <2% of the ~600 E3 ligases in the human genome have been exploited to produce proteolysis targeting chimeras (PROTACs), and the efficacy of the approach has not been demonstrated for a vital class of complex multi-subunit membrane proteins- ion channels. NEDD4-1 and NEDD4-2 are physiological regulators of myriad ion channels, and belong to the 28-member HECT (homologous to E6AP C-terminus) family of E3 ligases with widespread roles in cell/developmental biology and diverse diseases including various cancers, immunological and neurological disorders, and chronic pain. The potential efficacy of HECT E3 ligases for targeted protein degradation is unexplored, constrained by a lack of appropriate binders, and uncertain due to their complex regulation by layered intra-molecular and posttranslational mechanisms. Here, we identified a nanobody that binds with high affinity and specificity to a unique site on the N-lobe of the NEDD4-2 HECT domain at a location physically separate from sites critical for catalysis- the E2 binding site, the catalytic cysteine, and the ubiquitin exosite- as revealed by a 3.1 Å cryo-electron microscopy reconstruction. Recruiting endogenous NEDD4-2 to diverse ion channel proteins (KCNQ1, ENaC, and CaV2.2) using a divalent (DiVa) nanobody format strongly reduced their functional expression with minimal off-target effects as assessed by global proteomics, compared to simple NEDD4-2 overexpression. The results establish utility of a HECT E3 ligase for targeted protein downregulation, validate a class of complex multi-subunit membrane proteins as susceptible to this modality, and introduce endogenous E3 ligase recruitment with DiVa nanobodies as a general method to generate novel genetically-encoded ion channel inhibitors.

Structural and functional validation of a highly specific Smurf2 inhibitor.

Smurf1 and Smurf2 are two closely related member of the HECT (homologous to E6AP carboxy terminus) E3 ubiquitin ligase family and play important roles in the regulation of various cellular processes. Both were initially identified to regulate transforming growth factor-β and bone morphogenetic protein signaling pathways through regulating Smad protein stability and are now implicated in various pathological processes. Generally, E3 ligases, of which over 800 exist in humans, are ideal targets for inhibition as they determine substrate specificity; however, there are few inhibitors with the ability to precisely target a particular E3 ligase of interest. In this work, we explored a panel of ubiquitin variants (UbVs) that were previously identified to bind Smurf1 or Smurf2. In vitro binding and ubiquitination assays identified a highly specific Smurf2 inhibitor, UbV S2.4, which was able to inhibit ligase activity with high potency in the low nanomolar range. Orthologous cellular assays further demonstrated high specificity of UbV S2.4 toward Smurf2 and no cross-reactivity toward Smurf1. Structural analysis of UbV S2.4 in complex with Smurf2 revealed its mechanism of inhibition was through targeting the E2 binding site. In summary, we investigated several protein-based inhibitors of Smurf1 and Smurf2 and identified a highly specific Smurf2 inhibitor that disrupts the E2-E3 protein interaction interface.

Sequence-Dependent Interaction of the Human Papillomavirus E2 Protein with the DNA Elements on Its DNA Replication Origin.

The human papillomavirus (HPV) E2 protein is essential for regulating the initiation of viral DNA replication as well as the regulation of transcription of certain HPV-encoded genes. Its ability to recognize and bind to its four recognition sequences in the viral origin is a key step in the initiation of HPV DNA replication. Thus, understanding the mechanism of DNA binding by E2 protein and the unique roles played by individual DNA sequence elements of the replication origin is essential. We have purified the recombinant full-length HPV type 11 E2 protein. Quantitative DNA binding analysis indicated E2 protein bound all four DNA binding sites with reasonably high affinities but with distinct preferences. It bound its cognate binding sites 1, 2, and 4 with higher affinities, but bound binding site 3 with lower affinity. Analysis of binding to these sites unraveled multiple sequence elements that appeared to influence E2 binding affinity and target discrimination, including the sequence of spacer region, flanking sequences, and proximity of E2 binding sites. Thermodynamic analysis indicated hydrophobic interaction in the protein-DNA complex formation. Our studies indicate a large multi-protein complex formation on the HPV-origin DNA, likely due to reasonably high binding affinities as well as intrinsic oligomerization propensity of E2 dimers.

The correlation between methylation in HPV16 long control region and cervical intraepithelial neoplasia grade 2 or more: a Meta-analysis

Objective: To investigate the correlation between methylation in human papillomavirus 16 (HPV16) long control region (LCR) and cervical intraepithelial neoplasia grade ≥2 (CIN2+). Methods: The literature retrieval was conducted by using the databases of PubMed, Embase, Cochrane Library, Web of Science, CNKI, Wanfang data and Weipu according to the inclusion and exclusion criteria, and the retrieval period was from the establishment of the databases to February 27th, 2022. Software RevMan 5.3 and Stata 15.1 were used for Meta-analysis. Results: A total of 17 literatures were included involving 1 421 subjects. Results of Meta-analysis showed that OR of the correlation between methylation of HPV16 LCR and CIN2+ was 1.56 (95%CI: 0.70-3.47). Subgroup analysis showed that methylation of the 5' terminal, enhancer and promoter regions were not associated with CIN2+, while in four E2 binding sites (E2BS), the methylation of E2BS1, E2BS3 and E2BS4 increased the risk of CIN2+, with the ORs of 3.92 (95%CI: 1.92-7.99), 10.50 (95%CI: 3.67-30.04) and 3.65 (95%CI: 1.58-8.41), respectively. However, subgroup analysis on E2BS2 was not performed due to the limitation of the number of literatures. According to the different sources of population, the risk of CIN2+ in Chinese population was associated with methylation of HPV16 LCR (OR=2.14, 95%CI: 1.31-3.50). There was a correlation between the risk of CIN2+ and HPV16 LCR methylation in the population with pyrosequencing of HPV16 LCR, and OR was 1.75 (95%CI: 1.03-2.98). Conclusion: The risk of CIN2+ is correlated with the methylation of E2BS in HPV16 LCR, which can be used as potential biomarkers.

Quantitative Analysis of HPV E2 Binding to DNA Binding Sites and Sequence Variants

Many proteins, such as transcription factors, bind to DNA sequences within their genome to initiate different biological processes. In the human papillomavirus (HPV), the E2 protein controls the initiation of DNA replication through interaction with its binding sites. The HPV genome contains four binding sites for the E2 protein in a conserved spatial arrangement that frequently includes a 12 bp consensus sequence, ACCG(N4) CGGT. We have previously studied the strength of this interaction using the electrophoretic mobility shift assay (EMSA). The results showed that a single nucleotide variation in the E2 binding site consensus sequence can play a role in viral DNA replication. To expand on these findings and quantitatively correlate the binding affinity of the sequence variants, we further analyzed these interactions by expanding the previous binding studies. This project improved the initial binding affinity assay by incorporating an optimized recombinant protein and fluorescent probes. The qualitative binding results remained the same and to quantitatively observe the interaction we will be using surface plasmon resonance (SPR) to observe the Kon and Koff rates. Due to its conserved nature, the HPV E2 protein has been deemed a potential drug/therapeutic target. Hence, quantitative analysis of this interaction is important for drug development and therapeutic research.

2\u2032,3\u2032,4\u2032-Trihydroxychalcone changes estrogen receptor \u03b1 regulation of genes and breast cancer cell proliferation by a reprogramming mechanism

BackgroundMenopausal hormone therapy (MHT) is recommended for only five years to treat vasomotor symptoms and vulvovaginal atrophy because of safety concerns with long-term treatment. We investigated the ability of 2′,3′,4′-trihydroxychalcone (2′,3′,4′-THC) to modulate estrogen receptor (ER)-mediated responses in order to find drug candidates that could potentially prevent the adverse effects of long-term MHT treatment.MethodsTransfection assays, real time-polymerase chain reaction, and microarrays were used to evaluate the effects of 2′,3′,4′-THC on gene regulation. Radioligand binding studies were used to determine if 2′,3′,4′-THC binds to ERα. Cell proliferation was examined in MCF-7 breast cancer cells by using growth curves and flow cytometry. Western blots were used to determine if 2′,3′,4′-THC alters the E2 activation of the MAPK pathway and degradation of ERα. Chromatin immunoprecipitation was used to measure ERα binding to genes.ResultsThe 2′,3′,4′-THC/E2 combination produced a synergistic activation with ERα on reporter and endogenous genes in human U2OS osteosarcoma cells. Microarrays identified 824 genes that we termed reprogrammed genes because they were not regulated in U2OS-ERα cells unless they were treated with 2′,3′,4′-THC and E2 at the same time. 2′,3′,4′-THC blocked the proliferation of MCF-7 cells by preventing the E2-induced activation of MAPK and c-MYC transcription. The antiproliferative mechanism of 2′,3′,4′-THC differs from selective estrogen receptor modulators (SERMs) because 2′,3′,4′-THC did not bind to the E2 binding site in ERα like SERMs.ConclusionOur study suggests that 2′,3′,4′-THC may represent a new class of ERα modulators that do not act as a direct agonists or antagonists. We consider 2′,3′,4′-THC to be a reprogramming compound, since it alters the activity of ERα on gene regulation and cell proliferation without competing with E2 for binding to ERα. The addition of a reprogramming drug to estrogens in MHT may offer a new strategy to overcome the adverse proliferative effects of estrogen in MHT by reprogramming ERα as opposed to an antagonist mechanism that involves blocking the binding of estrogen to ERα.

Kaposi's sarcoma-associated herpesvirus ubiquitin ligases downregulate cell surface expression of l-selectin.

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic etiological factor for Kaposi's sarcoma and primary effusion lymphoma in immunocompromised patients. KSHV utilizes two immune evasion E3 ubiquitin ligases, namely K3 and K5, to downregulate the expression of antigen-presenting molecules and ligands of natural killer (NK) cells in the host cells through an ubiquitin-dependent endocytic mechanism. This allows the infected cells to evade surveillance and elimination by cytotoxic lymphocytes and NK cells. The number of host cell molecular substrates reported for these ubiquitin ligases is limited. The identification of novel substrates for these ligases will aid in elucidating the mechanism underlying immune evasion of KSHV. This study demonstrated that K5 downregulated the cell surface expression of l-selectin, a C-type lectin-like adhesion receptor expressed in the lymphocytes. Tryptophan residue located at the centre of the E2-binding site in the K5 RINGv domain was essential to downregulate l-selectin expression. Additionally, the lysine residues located at the cytoplasmic tail of l-selectin were required for the K5-mediated downregulation of l-selectin. K5 promoted the degradation of l-selectin through polyubiquitination. These results suggest that K5 downregulates l-selectin expression on the cell surface by promoting polyubiquitination and ubiquitin-dependent endocytosis, which indicated that l-selectin is a novel substrate for K5. Additionally, K3 downregulated l-selectin expression. The findings of this study will aid in the elucidation of a novel immune evasion mechanism in KSHV.

Heterogeneous nuclear ribonucleoprotein E1 binds polycytosine DNA and monitors genome integrity.

Heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1) is a tumor suppressor protein that binds site- and structure-specifically to RNA sequences to regulate mRNA stability, facilitate alternative splicing, and suppress protein translation on several metastasis-associated mRNAs. Here, we show that hnRNP E1 binds polycytosine-rich DNA tracts present throughout the genome, including those at promoters of several oncogenes and telomeres and monitors genome integrity. It binds DNA in a site- and structure-specific manner. hnRNP E1-knockdown cells displayed increased DNA damage signals including γ-H2AX at its binding sites and also showed increased mutations. UV and hydroxyurea treatment of hnRNP E1-knockdown cells exacerbated the basal DNA damage signals with increased cell cycle arrest, activation of checkpoint proteins, and monoubiquitination of proliferating cell nuclear antigen despite no changes in deubiquitinating enzymes. DNA damage caused by genotoxin treatment localized to hnRNP E1 binding sites. Our work suggests that hnRNP E1 facilitates functions of DNA integrity proteins at polycytosine tracts and monitors DNA integrity at these sites.

The molecular basis of OH-PCB estrogen receptor activation

Polychlorinated bisphenols (PCBs) continue to contaminate food chains globally where they concentrate in tissues and disrupt the endocrine systems of species throughout the ecosphere. Hydroxylated PCBs (OH-PCBs) are major PCB metabolites and high-affinity inhibitors of human estrogen sulfotransferase (SULT1E1), which sulfonates estrogens and thus prevents them from binding to and activating their receptors. OH-PCB inhibition of SULT1E1 is believed to contribute significantly to PCB-based endocrine disruption. Here, for the first time, the molecular basis of OH-PCB inhibition of SULT1E1 is revealed in a structure of SULT1E1 in complex with OH-PCB1 (4ʹ-OH-2,6-dichlorobiphenol) and its substrates, estradiol (E2), and PAP (3’-phosphoadenosine-5-phosphosulfate). OH-PCB1 prevents catalysis by intercalating between E2 and catalytic residues and establishes a new E2-binding site whose E2 affinity and positioning are greater than and competitive with those of the reactive-binding pocket. Such complexes have not been observed previously and offer a novel template for the design of high-affinity inhibitors. Mutating residues in direct contact with OH-PCB weaken its affinity without compromising the enzyme’s catalytic parameters. These OH-PCB resistant mutants were used in stable transfectant studies to demonstrate that OH-PCBs regulate estrogen receptors in cultured human cell lines by binding the OH-PCB binding pocket of SULT1E1.

The Mechanism of NEDD8 Activation of CUL5 Ubiquitin E3 Ligases

AbstractCullin RING E3 ligases (CRLs) ubiquitylate hundreds of important cellular substrates. Here we have assembled and purified the Ankyrin repeat and SOCS Box protein 9 CUL5 RBX2 ligase (ASB9-CRL) in vitro and show how it ubiquitylates one of its substrates, CKB. CRLs occasionally collaborate with RING between RING E3 ligases (RBRLs), and indeed, mass spectrometry analysis showed that CKB is specifically ubiquitylated by the ASB9-CRL-ARIH2-UBE2L3 complex. Addition of other E2s such as UBE2R1 or UBE2D2 contributes to polyubiquitylation but does not alter the sites of CKB ubiquitylation. Hydrogen–deuterium exchange mass spectrometry (HDX-MS) analysis revealed that CUL5 neddylation allosterically exposes its ARIH2 binding site, promoting high-affinity binding, and it also sequesters the NEDD8 E2 (UBE2F) binding site on RBX2. Once bound, ARIH2 helices near the Ariadne domain active site are exposed, presumably relieving its autoinhibition. These results allow us to propose a model of how neddylation activates ASB-CRLs to ubiquitylate their substrates.

The SMC5/6 Complex Represses the Replicative Program of High-Risk Human Papillomavirus Type 31.

The multi-subunit structural maintenance of chromosomes (SMC) 5/6 complex includes SMC6 and non-SMC element (NSE)3. SMC5/6 is essential for homologous recombination DNA repair and functions as an antiviral factor during hepatitis B (HBV) and herpes simplex-1 (HSV-1) viral infections. Intriguingly, SMC5/6 has been found to associate with high-risk human papillomavirus (HPV) E2 regulatory proteins, but the functions of this interaction and its role during HPV infection remain unclear. Here, we further characterize SMC5/6 interactions with HPV-31 E2 and its role in the HPV life cycle. Co-immunoprecipitation (co-IP) revealed that SMC6 interactions with HPV-31 E2 require the E2 transactivation domain, implying that SMC5/6 interacts with full-length E2. Using chromatin immunoprecipitation, we found that SMC6 is present on HPV-31 episomes at E2 binding sites. The depletion of SMC6 and NSE3 increased viral replication and transcription in keratinocytes maintaining episomal HPV-31, indicating that SMC5/6 restricts the viral replicative program. SMC6 interactions with E2 were reduced in the presence of HPV-31 E1, suggesting that SMC6 and E1 compete for E2 binding. Our findings demonstrate SMC5/6 functions as a repressor of the viral replicative program and this may involve inhibiting the initiation of viral replication.

Detailed Characteristics of Tonsillar Tumors with Extrachromosomal or Integrated Form of Human Papillomavirus.

The human papillomavirus (HPV) integration, the critical step in viral carcinogenesis, most frequently occurs in the E2 gene, which results in its inactivation and in an increase of E6/E7 transcription. However, in a substantial number of tumors, the virus is present in an extrachromosomal form. For those tumors, the transformation mechanisms are not fully elucidated. Here we evaluated the possible mechanism of inactivating the E2 without interruption of the gene, methylation or mutation of the E2 binding sites (E2BSs) in HPV16-positive tonsillar tumors by next-generation and Sanger sequencing. Viral genome status was analyzed by the amplification of papillomavirus oncogene transcripts assay (APOT) and mRNA mapping, and expression of viral oncogenes was performed by qPCR. The methylation of E2BSs was significantly higher in tumors with an integrated, in comparison to extrachromosomal, form of the viral genome. No mutations were detected in the E2BSs. The viral oncogenes were equally expressed in samples with an integrated and extrachromosomal form of the virus. Only the nucleotide variants were identified in the E2 gene. No proposed mechanism of E2 inactivation was confirmed in tonsillar tumors with an extrachromosomal form of the HPV genome. The expression of E6/E7 genes seems to be sufficient to initiate and maintain the carcinogenic process

E2 protein is the major determinant of specificity at the human papillomavirus origin of replication

The replication of human papillomavirus (HPV) genomes requires E1 and E2 proteins as the viral trans-factors and the replication origin, located in the URR, as a cis-element. The minimal requirements for an HPV replication origin vary among different virus types but always include one or more binding sites for the E2 protein. The requirements for an E1 binding site seem to vary among different HPV genera, with alpha-HPV11 and -18 minimal origins able to replicate without E1 binding site in contrast to beta-HPV8. In the present article, we analysed the sequence requirements for the beta-HPV5 minimal origin of replication. We show that the HPV5 URR is able to replicate in U2OS cells without the sequence proposed as an E1 binding site, albeit at lower levels than wt URR, given that three E2 binding sites are intact and both viral replication proteins are present. The lack of an absolute requirement of the E1 binding site for the origin of replication of HPV5 led us to analyse whether the viral E1 and E2 proteins from other HPV types are competent to support replication from this origin. Surprisingly, the E1 and E2 proteins from beta-HPV types support replication from the origin in contrast to proteins from alpha-HPV types 11, -16, or -18. Furthermore, the replication proteins E1 and E2 of these alpha-HPV types are unable to support the replication of HPV5 URR, even if the E1 binding site is intact. In light of these results, we performed a detailed analysis of the ability of different combinations of E1 and E2 proteins from various alpha- and beta-HPV types to support the replication of URR sequences from the respective HPV types in the U2OS cell line.

The molecular nature of the 17\u03b2-Estradiol binding site in the voltage- and Ca2+-activated K+ (BK) channel \u03b21 subunit

The accessory β1 subunit modulates the Ca2+- and voltage-activated K+ (BK) channel gating properties mainly by increasing its apparent Ca2+ sensitivity. β1 plays an important role in the modulation of arterial tone and blood pressure by vascular smooth muscle cells (SMCs). 17β-estradiol (E2) increases the BK channel open probability (Po) in SMCs, through a β1 subunit-dependent modulatory effect. Here, using molecular modeling, bioinformatics, mutagenesis, and electrophysiology, we identify a cluster of hydrophobic residues in the second transmembrane domain of the β1 subunit, including the residues W163 and F166, as the binding site for E2. We further show that the increase in Po induced by E2 is associated with a stabilization of the voltage sensor in its active configuration and an increase in the coupling between the voltage sensor activation and pore opening. Since β1 is a key molecular player in vasoregulation, the findings reported here are of importance in the design of novel drugs able to modulate BK channels.

Abstract 4653: Melanocyte specific deletion of Map3k1 reveals its role in BRAFV600E-driven melanoma

Abstract BRAF is the most common driver oncogene in cutaneous melanoma. Activating mutations in the BRAF gene are enriched in melanomas associated with intermittent sun exposure, with the most frequent mutations occurring at codon 600, leading to a constitutive activation of the RAF/MEK/ERK signaling pathway. In previous studies, we demonstrated that ultraviolet radiation (UVR) accelerates melanomagenesis in a mouse model of melanoma driven by BRAFV600E. From whole exome sequencing analysis of the tumors we found that Map3k1 was the most recurrently mutated gene across different experimental cohorts. MAP3K1 is unique in having both a kinase and E3 ligase function, allowing it to regulate protein phosphorylation and ubiquitin-mediated proteasome degradation. The vast majority of the mutations in Map3k1 occurred within the RING domain, which contains the E2 binding site for ubiquitin-conjugating enzymes. The most prevalent non-synonymous mutations where present in codon 484 and arose as a consequence of C-to-T transitions at a dipyrimidine site, characteristic of UVR-induced DNA damage. To understand better the role of MAP3K1, we generated Tyr::CreERT2+/o;Map3k1f/f mice allowing us to conditionally delete Map3k1 specifically in the melanocytes upon topical application of tamoxifen to the dorsal skin of juvenile mice. These mice did not develop tumors, but when crossed to mice carrying a Braf+/LSL-V600E allele, all mice develop melanoma, with a shorter latency and an increased multiplicity compared to Tyr::CreERT2+/o;Braf+/LSL-V600E mice. Tumors showed similar histopathological features, but melanomas carrying Map3k1 floxed or mutant variants presented higher levels of phosphorylated ERK1/2 than those with wild-type Map3k1. In addition, analysis of expression data of human cutaneous melanomas from The Cancer Genome Atlas showed an inverse correlation between the expression of MAP3K1 and ERK2 protein levels. Taken together, our results suggest that MAP3K1 loss-of-function cooperates with BRAFV600E to drive melanoma development by increasing MEK-ERK pathway activation. Citation Format: Lucas D. Trucco, Piyushkumar A. Mundra, Pablo Garcia-Martinez, Kate Hogan, Nathalie Dhomen, Valeria Pavet, Richard Marais. Melanocyte specific deletion of Map3k1 reveals its role in BRAFV600E-driven melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4653.

Study on the relationship between methylation status of HPV 16 E2 binding sites and cervical lesions

BackgroundThe aim of this study was to investigate the methylation status of E2BSs in the HPV 16 long control region (LCR) in clinical cervical samples. MethodsMethylation status of the four E2BSs in 43 clinical cervical samples with HPV 16 infection was quantitatively detected using pyrosequencing. Meanwhile, Quantivirus® HPV E6/E7 RNA 3.0 assay (bDNA) was used to detect E6/E7 mRNA levels in the corresponding specimens. ResultsOur results showed that methylation status of E2BS1, 2 and 4 sites in high-grade squamous intraepithelial lesions (HSIL) and cervical cancer were significantly higher than that of asymptomatic HPV 16 infection and low-grade squamous intraepithelial lesions (LSIL) (all P < .05). Furthermore, methylation status of HPV 16 E2BS1 and 2 was positively correlated with E6/E7 mRNA levels (rs = 0.529 and 0.512 respectively, P < .01). Receiver operating characteristic curve analysis was used to compare the diagnostic performance of E2BSs methylation. When the Youden index was the maximum value, the methylation level of E2BS1 and E2BS2 all demonstrated optimum diagnostic sensitivity of 77.8%, and specificity of 80% and 92%, respectively. ConclusionsThe methylation status of E2BS1 and 2 may have utility as diagnostic markers for the severity of cervical lesions in the future.

The role of HPV16 regulatory region methylation in viral oncogenes E6 and E7 eхpression in primary cervical cancer lesions

Background.Overexpression of the human papillomavirus oncogenes E6 and E7 is a major factor in initiation and progression of HPV-induced tumors. Inactivation of negative regulatory function of E2 protein – the main viral transcription and replication regulator – is considered to be an important mechanism leading to the viral oncogenes overexpression. It is known that the loss of E2 functions occurs due to disruption of E2 open reading frame during the viral DNA integration into a cell genome in a part of HPV-positive tumors. An alternative mechanism of E2 function blocking in tumors retained its expression can be methylation of the HPV regulatory region, since it is known that E2 is incapable to bind its methylated binding sites.The study objectiveis to analyze methylation of the HPV16 regulatory region and expression of the viral E6 and E7 oncogenes in E2 expressing or non-expressing clinical samples of cervical cancer.Results.It has been demonstrated that the level of the HPV16 URR methylation in E2-expressing lesions is significantly higher than that in non-expressing cervical cancer lesions. Demethylation of the HPV16 promoter in cervical cell line Caski is followed by decrease of the viral E6 и E7 oncogenes mRNA levels, supporting the hypothesis that methylation is necessary for effective E6 and E7 transcription and indicates on restitution of E2 regulatory function in E2-expressing cervical cancer cells.Conclusion.These data suggest that methylation of E2 binding sites in HPV16 regulatory region blocking E2 protein binding represents an important mechanism ensuring high level of the viral E6 and E7 oncogenes expression.

Synergistic recruitment of UbcH7~Ub and phosphorylated Ubl domain triggers parkin activation

The E3 ligase parkin ubiquitinates outer mitochondrial membrane proteins during oxidative stress and is linked to early‐onset Parkinson's disease. Parkin is autoinhibited but is activated by the kinase PINK1 that phosphorylates ubiquitin leading to parkin recruitment, and stimulates phosphorylation of parkin's N‐terminal ubiquitin‐like (pUbl) domain. How these events alter the structure of parkin to allow recruitment of an E2~Ub conjugate and enhanced ubiquitination is an unresolved question. We present a model of an E2~Ub conjugate bound to the phospho‐ubiquitin‐loaded C‐terminus of parkin, derived from NMR chemical shift perturbation experiments. We show the UbcH7~Ub conjugate binds in the open state whereby conjugated ubiquitin binds to the RING1/IBR interface. Further, NMR and mass spectrometry experiments indicate the RING0/RING2 interface is re‐modelled, remote from the E2 binding site, and this alters the reactivity of the RING2(Rcat) catalytic cysteine, needed for ubiquitin transfer. Our experiments provide evidence that parkin phosphorylation and E2~Ub recruitment act synergistically to enhance a weak interaction of the pUbl domain with the RING0 domain and rearrange the location of the RING2(Rcat) domain to drive parkin activity.

Two Novel, Distantly Related Papillomaviruses Isolated from Healthy Skin of the Timor Deer (Rusa timorensis).

ABSTRACTWe report the complete genome sequences of Rusa timorensis papillomavirus 1 (RtimPV1) and Rusa timorensis papillomavirus 2 (RtimPV2), isolated from hair follicles of asymptomatic skin from the same Timor deer specimen. RtimPV1 and RtimPV2 are evolutionarily only distantly related. RtimPV1 lacks a canonical E2-binding site, and RtimPV2 does not carry an E6 gene.

Intracellular antibody signalling is regulated by phosphorylation of the Fc receptor TRIM21.

Cell surface Fc receptors activate inflammation and are tightly controlled to prevent autoimmunity. Antibodies also simulate potent immune signalling from inside the cell via the cytosolic antibody receptor TRIM21, but how this is regulated is unknown. Here we show that TRIM21 signalling is constitutively repressed by its B-Box domain and activated by phosphorylation. The B-Box occupies an E2 binding site on the catalytic RING domain by mimicking E2-E3 interactions, inhibiting TRIM21 ubiquitination and preventing immune activation. TRIM21 is derepressed by IKKβ and TBK1 phosphorylation of an LxxIS motif in the RING domain, at the interface with the B-Box. Incorporation of phosphoserine or a phosphomimetic within this motif relieves B-Box inhibition, promoting E2 binding, RING catalysis, NF-κB activation and cytokine transcription upon infection with DNA or RNA viruses. These data explain how intracellular antibody signalling is regulated and reveal that the B-Box is a critical regulator of RING E3 ligase activity.