The Basally Expressed p53-Mediated Homeostatic Function

Apart from mutations in the p53 gene, p53 functions can be alternatively compromised by a decrease in nuclear p53 protein levels or activities. In accordance, enhanced p53 protein turnover due to elevated expression of the critical p53 E3 ligase MDM2 or MDM2/MDMX is found in many human cancers. Likewise, the HPV viral E6 protein-mediated p53 degradation critically contributes to the tumorigenesis of cervical cancer. In addition, growth-promoting signaling-induced cell proliferation is accompanied by p53 downregulation. Animal studies have also shown that loss of p53 is essential for oncogenes to drive malignant transformation. The close association between p53 downregulation and carcinogenesis implicates a critical role of basally expressed p53. In accordance, available evidence indicates that a reduced level of basal p53 is usually associated with disruption of homeostasis, suggesting a homeostatic function mediated by basal p53. However, basally expressed p53 under non-stress conditions is maintained at a relatively low abundance with little transcriptional activity, raising the question of how basal p53 could protect homeostasis. In this review, we summarize the findings pertinent to basal p53-mediated activities in the hope of developing a model in which basally expressed p53 functions as a barrier to anabolic metabolism to preserve homeostasis. Future investigation is necessary to characterize basal p53 functionally and to obtain an improved understanding of p53 homeostatic function, which would offer novel insight into the role of p53 in tumor suppression.

Investigation of potential antiviral natural products with an effect on HPV18 E6 protein by molecular docking method

Background: Infection with the Human Papillomavirus (HPV) causes cellular dysplasia, which leads to cervical cancers in women and penile or rectal cancers in men. Objective: This in silico study identified the plant compounds with potential therapeutic effects against HPV 18 oncogenic virus using the molecular docking method. Methods: The three-dimensional (3D) structure of HPV18 E6 protein, as the target protein, and the 3D structure of plant compounds with potential therapeutic effect against viruses, as ligands, was obtained from the protein databases (RCSB) and PubChem, respectively. Both structures of ligands and target protein were subjected to AutoDock tools-1.5.6, ver.4 separately. The structure with the most negative affinity was docked to reconsider its connection location. The results were analyzed more based on pharmacodynamic and pharmacokinetic parameters. Results: The docking of HPV18 E6 protein with 19 selected ligands resulted in four compounds, curcumin, silymarin, saikosaponin c, and lactupicrin, showing the best docking scores; they had better binding free energies with HPV E6 protein. Among four compounds against HPV18 E6, silymarin and curcumin were less dangerous than other compounds due to the lack of inhibition of the human Ether-à-go-go-Related Gene (hERG). Of these two compounds, silymarin had lower oral absorption, lactopicrin had less skin absorption, lactopicrin is the substrate of P-gp, and saikosaponin c crosses the blood-brain barrier. Conclusion: Among potential antiviral plants against HPV18E6, four compounds were found to be effective. According to these findings, it is recommended that in vitro and in vivo examinations be conducted to determine the effectiveness of these compounds against HPV18 Keywords: Biological products, Antiviral agents, HPV18, Molecular docking, Computational biology, E6 protein

Regulation of O-Linked N-Acetyl Glucosamine Transferase (OGT) through E6 Stimulation of the Ubiquitin Ligase Activity of E6AP

Glycosyltransferase OGT catalyzes the conjugation of O-linked β-D-N-acetylglucosamine (O-GlcNAc) to Ser and Thr residues of the cellular proteins and regulates many key processes in the cell. Here, we report the identification of OGT as a ubiquitination target of HECT-type E3 ubiquitin (UB) ligase E6AP, whose overexpression in HEK293 cells would induce the degradation of OGT. We also found that the expression of E6AP in HeLa cells with the endogenous expression of the E6 protein of the human papillomavirus (HPV) would accelerate OGT degradation by the proteasome and suppress O-GlcNAc modification of OGT substrates in the cell. Overall, our study establishes a new mechanism of OGT regulation by the ubiquitin­–proteasome system (UPS) that mediates the crosstalk between protein ubiquitination and O-GlcNAcylation pathways underlying diverse cellular processes.

Metabolic rewiring is associated with HPV-specific profiles in cervical cancer cell lines

Both HPV-positive and HPV-negative cervical cancers are associated with aberrant metabolism, although the oncogenic drivers remain elusive. Here we show the assessment of the metabolomic profiles of four distinct cervical cell lines, a normal and three cancer cell lines, one HPV-negative (C33A) and two HPV-positive (SiHa HPV16+, HeLa HPV18+), employing an ultra performance liquid chromatography and a high resolution mass spectrometry. Out of the total 462 metabolites, 248 to 326 exhibited statistically significant differences, while Random Forests analysis identified unique molecules for each cell line. The two HPV+ cell lines exhibited features of Warburg metabolism, consistent with the role of the HPV E6 protein. SiHa and HeLa cells displayed purine salvage pathway activity, while C33A cells revealed synthesis of cytidine, via a novel mechanism. These data document a highly dynamic HPV-specific rewiring of metabolic pathways occurring in cervical cancer. Therefore, this approach can eventually provide novel mechanistic insights into cervical carcinogenesis.

Prognosis of endometrial cancer depends on intracrine ratio of sex steroids.

e17564 Background: Local imbalance of sex steroids (SS) plays a leading role in the development of gynecologic tumors. The purpose of the study was to investigate the effect of changes in SS and E6 protein levels on the course of endometrial cancer (EC). Methods: 50 patients with EC T1-2N0M0 (histologically - endometrioid adenocarcinoma, AC), aged 53.4±3.2 years, were recruited. Levels of SS and E6 protein were determined by standard ELISA systems in tumor samples. The coefficient of estrogens to the amount of testosterone and progesterone – C = (E1+E2):(T+P4) was calculated. Intact endometrium (IE) obtained in surgical treatment for uterine fibroids was used as the intact tissue. Results: AC patients demonstrated elevated estrone (E1) levels, compared to IE: by 2.2 times in 88% and by 5.9 times in 12% cases (p < 0.05). Levels of estradiol (E2) were similar in AC and IE. Progesterone (P4) levels in 32 patients were 1.5 times lower than in IE, and testosterone (T) 1.5 times higher (p < 0.05). P4 in 18 patients was 3 times lower than in IE, and T – 1.4 times lower in 12 women and 2.2 times lower in 6 women (p < 0.05). The C coefficient increased in 32 patients by 1.3 times (p< 0.05), in 12 patients by 2.7 times, in 6 patients by 8.2 times (p < 0.05). E6 protein was found in tumor tissue of 18 patients with elevated C. 6 of 18 women with C = 24.54±2.4 and E6 = 420±32 ng/g of tissue developed recurrence during 6 months, and 12 patients with C = 8.15±1.2 and E6 = 28±2.1 ng/g of tissue developed recurrence in a period of 6 months to 1 year. Women with C = 4.04±0.39 without E6 oncoprotein in tumor tissue had a relapse-free period for more than 1 year. Conclusions: An analysis of C and E6 oncoprotein in tumor tissues allows identification of high-risk patients and a personalized approach to adequate treatment.

Efficacy of Mutant HPV-16 E6 Proteins in p53 Degradation

Background and Objective: High-risk human papilloma viruses (HPV) are the causative agent in the majority of anal, cervical, vaginal, vulvar, penile, and oropharyngeal cancers with an annual incidence of 630,000 cases world-wide. These viruses initially cause dysplasia that subsequently increases neoplasia risk. HPV’s encode eight major viral proteins with the E6 protein being crucial for replication. E6 binding to ubiquitin ligase E6AP initiates polyubiquitination of p53, targeting the protein for proteasomal degradation. We are taking a novel approach to inhibit HPV16+ dysplasia and cancers by designing inhibitors targeting specific amino acids of 16E6, which reside in the E6-E6AP binding pocket, thereby preventing p53 degradation. To affirm interaction with the targeted side chain, we generated E6 point mutations that serve as specificity controls. These mutations are designed to disrupt interaction with the compound. To ensure their suitability for our studies, we are herein characterizing their capacity to bind E6AP and bind and degrade p53. Methods: E6 mutants were generated by site-directed mutagenesis and analyzed by sequencing. H1299 cells were transfected with GFP, wild-type (WT) E6, or mutant HPV-16 E6 plasmids +/- WT p53 plasmid. After 48 hours, cells are lysed and 16E6 was immunoprecipitated. Proteins bound to 16 E6 were separated by SDS-PAGE and subjected to western blot. Binding to E6AP and p53 was analyzed and presence of 16E6 was confirmed by immunoblotting. To test for p53 degradation, H1299 cells were transfected with firefly luciferase (Fluc) (transfection control) and p53-luciferase along with WT E6, mutant E6 proteins, or empty LXSN plasmid. After 24 hours p53-luciferase was measured with Dual-Glo Luciferase Assay. Results: To be determined Conclusion: To be determined

HPV E6 Protein Associated SOX21-AS1 Promotes YAP/TAZ Activation by Attenuating YAP1 Ubiquitination in Human Cervical Cancer

Background: The human papillomavirus (HPV), especially HPV 16 type infection, is one of the well-known causes for human cervical cancer, we sought to investigate HPV 16 regulating lncRNA and its role in cervical carcinogenesis. Methods: The potential HPV16 related lncRNAs were screened by using bioinfomatic analysis. The relationship between SOX21-AS1 and clinical features was studied by using clinical samples. Its oncogenic roles were explored in vitro. Results: A HPV 16 infection-specific lncRNA, SOX21-AS1 was spotted by screening the Cancer Genome Atlas TCGA database, and its expression was seriously related to Hippo signaling pathway by using Gene Set Enrichment Analysis. Total 40 cases patients suffered from cervical carcinomas (CCs) were involved, we found that SOX21-AS1 was over-expressed in those CCs patients who were positive for HPV 16 infection compared to those who were negative. We also found that SOX21-AS1 expression was positively related to E6 protein but not E7 expression, which is a carcinogenic protein of HPV 16. Also, YAP1/TAZ/TEAD complex can increase SOX21-AS1 transcription by binding to its promoter region. SOX21-AS1 can promote cell proliferation and invasion in CCs cell lines in a YAP1 activation-dependent manner. We found that SOX21-AS1 can promote YAP1 activation by preventing YAP1 phosphorylation at s127 residue and further preventing its degradation by binding to 14-3-3. Conclusion: In conclusion, SOX21-AS1 is an HPV16 specific lncRNA which can promote tumor growth and metastasis by targeting the Hippo signaling pathway.