USP15 inhibits HPV16 E6 degradation and catalytically inactive USP15 has reduced inhibitory activity

Alterations of UHRF family Expression and was regulated by High Risk Type HPV16 in Uterine Cervical Cancer

The altered protein expression of inverted CCAAT box-binding protein of 90 kDa/ubiquitin-like with PHD and RING finger domains 1 (ICBP90/UHRF1), and Np95-like ring finger protein (NIRF)/UHRF2, which belong to the ubiquitin-like with PHD and RING finger domains (UHRF) family, is linked to tumor malignancy and the progression of various cancers. In this study, we analyzed the UHRF family expression in cervical cancers, and it's regulation by human papillomavirus (HPV). Western blotting was performed to analyze protein expression in cervical cancer cell lines. Immunohistochemical analysis were used to investigate the expression of UHRF family and MIB-1 in cervical cancer tissues. Transfection were done for analyze the relationship between UHRF family and HPVs. We showed that NIRF expression was decreased and ICBP90 expression was increased in cervical cancers compared to normal counterparts. Western blotting also showed that NIRF expression was quite low levels, but ICBP90 was high in human cervical cancer cell lines. Interestingly, ICBP90 was up regulated by high risk type HPV16 E6 and E7, but not low-risk type HPV11. On the other hand, NIRF was down regulated by high risk type HPV16 E6 but not by E7. Low risk type HPV11 E6 did not affect the NIRF expression at all. We propose that ICBP90 overexpression, and reduced NIRF expression, found in cervical cancers, is an important event of a cervical carcinogenesis, and especially ICBP90 may offer a proliferating marker and therapeutic target for treating uterine cervical cancers.

Hypoxia-induced paclitaxel resistance in cervical cancer modulated by miR-100 targeting of USP15

Objective

Hypoxia, which occurs during the development of cervical cancer, confers chemotherapy resistance. MicroRNA expression is regulated by hypoxia and is associated with the onset and progression of certain types of cancer. MicroRNA-100 (miR-100) is a microRNA, associated with nasopharyngeal and oral squamous cell carcinomas, whose expression is decreased in cervical cancer. This study aims to ascertain the effect of hypoxia on expression levels of both miR-100 and its target genes, as well as exploring the sensitivity to paclitaxel under hypoxic conditions.

Methods

We investigated the effect of hypoxia on miR-100 expression. We also explored the regulators of paclitaxel response under hypoxic conditions of cervical cancer.

Results

Using RT-qPCR, we found that expression of miR-100 in cervical cancer cell lines SiHa and HeLa is significantly higher under hypoxic conditions (1% O₂). We also confirmed that human ubiquitin-specific protease 15 (USP15) is the one of the target proteins of miR-100. Hypoxia and overexpression of miR-100 both reduced the activity of the luciferase reporter containing the 3'-untranslated region of USP15, which contains the miR-100 binding site. Furthermore, a western blot analysis showed that hypoxia suppresses the expression of the USP15 protein, while RT-qPCR showed hypoxia-induced downregulation of USP15 mRNA levels. We also discovered that overexpression of miR-100 induces paclitaxel resistance, thereby reducing the drug's therapeutic effect on cell death.

Conclusions

Our results are consistent with the hypothesis that cervical cancer cells overexpress miR-100 in response to hypoxia and that miR-100 is a facilitator of USP15 downregulation and inactivation.

Proteases and HPV-Induced Carcinogenesis

Simple Summary

Human papillomavirus (HPV) infection is a sexually transmitted disease with high prevalence worldwide. Although most HPV infections do not lead to cancer, some HPV types are correlated with the majority of cervical cancers, and with some anogenital and oropharyngeal cancers. Moreover, enzymes known as proteases play an essential role in the pathogenic process in HPV-induced carcinogenesis. This review highlights the role of proteases and recent epidemiological data regarding HPV-dependent carcinogenesis.

Abstract

Persistent infection with Human papillomavirus (HPV) is the main etiologic factor for pre-malignant and malignant cervical lesions. Moreover, HPV is also associated with oropharynx and other anogenital carcinomas. Cancer-causing HPV viruses classified as group 1 carcinogens include 12 HPV types, with HPV 16 and 18 being the most prevalent. High-risk HPVs express two oncoproteins, E6 and E7, the products of which are responsible for the inhibition of p53 and pRB proteins, respectively, in human keratinocytes and cellular immortalization. p53 and pRB are pleiotropic proteins that regulate the activity of several signaling pathways and gene expression. Among the important factors that are augmented in HPV-mediated carcinogenesis, proteases not only control processes involved in cellular carcinogenesis but also control the microenvironment. For instance, genetic polymorphisms of matrix metalloproteinase 1 (MMP-1) are associated with carcinoma invasiveness. Similarly, the serine protease inhibitors hepatocyte growth factor activator inhibitor-1 (HAI-1) and -2 (HAI-2) have been identified as prognostic markers for HPV-dependent cervical carcinomas. This review highlights the most crucial mechanisms involved in HPV-dependent carcinogenesis, and includes a section on the proteolytic cascades that are important for the progression of this disease and their impact on patient health, treatment, and survival.

Inhibition of USP15 ameliorates high-glucose-induced oxidative stress and inflammatory injury in podocytes through regulation of the Keap1/Nrf2 signaling

Ubiquitin-specific peptidase 15 (USP15) is implicated in the pathogenesis of numerous diseases. However, whether USP15 plays a role in diabetic nephropathy remains undetermined. This project was designed to determine the potential role of USP15 in mediating high glucose (HG)-induced podocyte injury, a key event in the pathogenesis of diabetic nephropathy. We found that USP15 levels were elevated in podocytes after HG stimulation. Inhibition of USP15 led to decreases in HG-evoked apoptosis, oxidative stress, and inflammation in podocytes. Further investigation showed that inhibition of USP15 enhanced the activation of NF-E2-related factor 2 (Nrf2) and expression of Nrf2 target genes in HG-simulated podocytes. Moreover, depletion of Kelch-like ECH-associated protein 1 (Keap1) diminished the regulatory effect of USP15 inhibition on Nrf2 activation. In addition, Nrf2 suppression reversed USP15-inhibition-induced protective effects in HG-injured podocytes. Taken together, these data indicate that USP15 inhibition protects podocytes from HG-induced injury by enhancing Nrf2 activation via Keap1.

USP15: a review of its implication in immune and inflammatory processes and tumor progression

The covalent post-translational modification of proteins by ubiquitination not only influences protein stability and half-life, but also several aspects of protein function including enzymatic activity, sub-cellular localization, and interactions with binding partners. Protein ubiquitination status is determined by the action of large families of ubiquitin ligases and deubiquitinases, whose combined activities regulate many physiological and cellular pathways. The Ubiquitin Specific Protease (USP) family is one of 8 subfamilies of deubiquitinating enzymes composed of more than 50 members. Recent studies have shown that USP15 plays a critical role in regulating many aspects of immune and inflammatory function of leukocytes in response to a broad range of infectious and autoimmune insults and following tissue damage. USP15 regulated pathways reviewed herein include TLR signaling, RIG-I signaling, NF-kB, and IRF3/IRF7-dependent transcription for production of pro-inflammatory cytokines and type I interferons. In addition, USP15 has been found to regulate pathways implicated in tumor onset and progression such as p53, and TGF-β signaling, but also influences the leukocytes-determined immune and inflammatory microenvironment of tumors to affect progression and outcome. Hereby reviewed are recent studies of USP15 in model cell lines in vitro, and in mutant mice in vivo with reference to available human clinical datasets.

Ubiquitination of the HPV Oncoprotein E6 Is Critical for E6/E6AP-Mediated p53 Degradation

High-risk Human papillomaviruses (HPVs) types are associated with more than 90% of premalignant and malignant squamous lesions of the uterine cervix. The E6 oncoprotein of high-risk HPVs is a key determinant in cell transformation because it induces the degradation of the host pro-apoptotic tumor suppressor p53. E6 recruits the intracellular ubiquitin ligase E6AP and subsequently induces proteasome-dependent p53 degradation. Neither E6 nor E6AP alone interact with p53; however, the precise mechanism of the functional regulation of the E6/E6AP/p53 complex is unclear. Here, we showed that the high-risk HPV E6 proteins are ubiquitinated during E6/E6AP/p53 complex assembly and degraded by the proteasome system. Increasing p53 expression enhanced E6/E6AP/p53 assembly and facilitated E6 ubiquitination and degradation. The dominant negative mutant of p53 R175H, which does not efficiently bind E6, decreased E6 ubiquitination and increased stability. Furthermore, we showed that the ubiquitin ligase E6AP is essential for E6 ubiquitination, and downregulation of E6AP expression increased E6 stability. We also showed that p53 R175H inhibited E6-mediated p53 degradation. Consistently, the host deubiquitinating enzyme USP15 removed ubiquitin chains from E6 proteins and inhibited E6-mediated p53 degradation. Crucially, ectopic expression of either p53 R175H or USP15 promoted p53-triggered apoptosis in human cervical cancer cells. Considering the importance of ubiquitinated E6 on p53 degradation, the disruption of E6 ubiquitination represents an attractive pharmacological intervention against HPV-positive human cervical cancer.