ISG15

Gene Summary

Gene:ISG15; ISG15 ubiquitin-like modifier
Aliases: G1P2, IP17, UCRP, IFI15, IMD38, hUCRP
Location:1p36.33
Summary:The protein encoded by this gene is a ubiquitin-like protein that is conjugated to intracellular target proteins upon activation by interferon-alpha and interferon-beta. Several functions have been ascribed to the encoded protein, including chemotactic activity towards neutrophils, direction of ligated target proteins to intermediate filaments, cell-to-cell signaling, and antiviral activity during viral infections. While conjugates of this protein have been found to be noncovalently attached to intermediate filaments, this protein is sometimes secreted. [provided by RefSeq, Dec 2012]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:ubiquitin-like protein ISG15
HPRD
Source:NCBIAccessed: 25 June, 2015

Ontology:

What does this gene/protein do?
Show (13)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 25 June 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Antineoplastic Agents
  • Cancer Stem Cells
  • Neoplastic Cell Transformation
  • Tongue Neoplasms
  • Squamous Cell Carcinoma
  • Chromosome 1
  • Ubiquitin
  • Cytokines
  • Sulfotransferases
  • Transcription Factors
  • Cell Proliferation
  • Interferon-alpha
  • Phosphorylation
  • STAT1 Transcription Factor
  • Neoplasm Proteins
  • Gene Expression
  • Disease-Free Survival
  • Signal Transduction
  • Trans-Activators
  • Cultured Cells
  • Gene Expression Profiling
  • RTPCR
  • DNA-Binding Proteins
  • Cell Cycle
  • Messenger RNA
  • COS Cells
  • Immunohistochemistry
  • RNA Interference
  • Tamoxifen
  • siRNA
  • Cell Differentiation
  • Breast Cancer
  • ras Proteins
  • Cancer Gene Expression Regulation
  • Tumor Markers
  • Cervical Cancer
  • Interferons
  • Oligonucleotide Array Sequence Analysis
  • Apoptosis
  • Melanoma
  • CD Antigens
Tag cloud generated 25 June, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: ISG15 (cancer-related)

Sainz B, Martín B, Tatari M, et al.
ISG15 is a critical microenvironmental factor for pancreatic cancer stem cells.
Cancer Res. 2014; 74(24):7309-20 [PubMed] Related Publications
Cancer stem cells (CSC) are thought to play a major role in the development and metastatic progression of pancreatic ductal adenocarcinoma (PDAC), one of the deadliest solid tumors. Likewise, the tumor microenvironment contributes critical support in this setting, including from tumor stromal cells and tumor-associated macrophages (TAM) that contribute structural and paracrine-mediated supports, respectively. Here, we show that TAMs secrete the IFN-stimulated factor ISG15, which enhances CSC phenotypes in PDAC in vitro and in vivo. ISG15 was preferentially and highly expressed by TAM present in primary PDAC tumors resected from patients. ISG15 was secreted by macrophages in response to secretion of IFNβ by CSC, thereby reinforcing CSC self-renewal, invasive capacity, and tumorigenic potential. Overall, our work demonstrates that ISG15 is a previously unrecognized support factor for CSC in the PDAC microenvironment with a key role in pathogenesis and progression.

Kim ST, Sohn I, DO IG, et al.
Transcriptome analysis of CD133-positive stem cells and prognostic value of survivin in colorectal cancer.
Cancer Genomics Proteomics. 2014 Sep-Oct; 11(5):259-66 [PubMed] Related Publications
BACKGROUND/AIM: CD133 is an important, but not exclusive, biomarker of colorectal cancer (CRC) stem cells.
MATERIALS AND METHODS: In order to identify other CRC stem cell-specific genes, we performed a comparative expression profiling of CD133(+) and CD133(-) cell populations in primary and metastatic tumors from four patients with CRC. CD133(+) and CD133(-) CRC cells were isolated using MagSweeper and used for whole-transcriptome analysis with RNA-Seq.
RESULTS: We found that in CD133(+) cells, 17 genes (RNASE2, PRB2, IL4, MGC27382, CLEC4C, SALL3, GIMAP1, ISG15, LOC728875, ZIK1, ICAM2, CCDC7, CDYL2, LRRC2, ZEB1, OSTF1 and CCDC144B) were significantly up-regulated compared to CD133(-) CRC cells. Among them, IL4 has been known as an inducer of survivin implicated in the survival and proliferation of cancer cells. However, the prognostic value of survivin in CRC is controversial. We evaluated survivin expression in formalin-fixed paraffin-embedded tumor samples of 188 patients with CRC by immunohistochemistry. Survivin over-expression was detected in 85 patients (45.2%) and was significantly associated with primary tumor sites (p=0.028), lymph node metastasis (p=0.029) and advanced III/IV CRC stages (AJCC 7; p=0.001). Furthermore, survivin up-regulation correlated with reduced disease-free survival (DFS; p=0.021) and overall survival (OS; p<0.000) and was proved to be an independent prognostic factor for both DFS and OS in multivariate analysis.
CONCLUSION: Our data suggest that CD133(+) CRC stem cells have a distinct expression pattern and that survivin, up-regulated by differentially expressed IL-4, is a candidate biomarker for the prediction of recurrence and survival in CRC.

Huang YF, Bulavin DV
Oncogene-mediated regulation of p53 ISGylation and functions.
Oncotarget. 2014; 5(14):5808-18 [PubMed] Free Access to Full Article Related Publications
Oncogene-mediated cellular transformation is a multistep process involving activation of growth-promoting pathways as well as inactivation of tumor suppressors. We recently found that ISGylation of the p53 tumor suppressor is an important novel mechanism to control its stability. Here we identified that Isg15-dependent regulation of p53 can be enhanced by different oncogenes. We further show that the Src-mediated phosphorylation of p53 on Tyr126 and Tyr220 has a positive effect on p53 ISGylation by enhancing Herc5 binding. In turn, deletion of Isg15 results in accumulation and activation of native p53 in transformed cells thus increasing its anti-cancer activity and suppressing tumorigenesis in mice. We propose that Isg15-dependent degradation of p53 is an alternative pathway for oncogenes to regulate p53 activity, and thus is an attractive pathway for development of new anti-cancer drugs.

Li P, Harris D, Liu Z, et al.
STAT3-activated GM-CSFRα translocates to the nucleus and protects CLL cells from apoptosis.
Mol Cancer Res. 2014; 12(9):1267-82 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
UNLABELLED: Here, it was determined that chronic lymphocytic leukemia (CLL) cells express the α subunit, but not the β subunit, of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR/CSF2R). GM-CSFRα was detected on the surface, in the cytosol, and in the nucleus of CLL cells via confocal microscopy, cell fractionation, and GM-CSFRα antibody epitope mapping. Because STAT3 is frequently activated in CLL and the GM-CSFRα promoter harbors putative STAT3 consensus binding sites, MM1 cells were transfected with truncated forms of the GM-CSFRα promoter, then stimulated with IL6 to activate STAT3 and to identify STAT3-binding sites. Chromatin immunoprecipitation (ChIP) and an electoromobility shift assay (EMSA) confirmed STAT3 occupancy to those promoter regions in both IL6-stimulated MM1 and CLL cells. Transfection of MM1 cells with STAT3-siRNA or CLL cells with STAT3-shRNA significantly downregulated GM-CSFRα mRNA and protein levels. RNA transcripts, involved in regulating cell survival pathways, and the proteins KAP1 (TRIM28) and ISG15 coimmunoprecipitated with GM-CSFRα. GM-CSFRα-bound KAP1 enhanced the transcriptional activity of STAT3, whereas GM-CSFRα-bound ISG15 inhibited the NF-κB pathway. Nevertheless, overexpression of GM-CSFRα protected MM1 cells from dexamethasone-induced apoptosis, and GM-CSFRα knockdown induced apoptosis in CLL cells, suggesting that GM-CSFRα provides a ligand-independent survival advantage.
IMPLICATIONS: Constitutively, activation of STAT3 induces the expression of GM-CSFRα that protects CLL cells from apoptosis, suggesting that inhibition of STAT3 or GM-CSFRα may benefit patients with CLL.

Malilas W, Koh SS, Lee S, et al.
Suppression of autophagic genes sensitizes CUG2-overexpressing A549 human lung cancer cells to oncolytic vesicular stomatitis virus-induced apoptosis.
Int J Oncol. 2014; 44(4):1177-84 [PubMed] Related Publications
We showed in our previous study that cancer upregulated gene (CUG) 2, a novel oncogene, confers resistance to infection of oncolytic vesicular stomatitis virus (VSV) by activating Stat1-mediated signal transduction. Since many studies have reported that autophagy is involved in virus replication, we investigated whether autophagy also plays a role in the antiviral activity in A549 cells overexpressing CUG2 (A549-CUG2). We suppressed Atg5 or Beclin 1 expression using siRNA and examined its effect on the susceptibility of cells to infection by oncolytic VSV. We found that A549-CUG2 cells treated with Atg5 or Beclin 1 siRNA became susceptible to VSV infection, whereas A549-CUG2 cells treated with control siRNA were resistant. This result suggests that autophagy is involved in the antiviral response of A549-CUG2 cells. Further investigation revealed that autophagy impairment enhanced the generation of reactive oxygen species (ROS), which resulted in inactivation of S6 kinase. Under these conditions, the levels of ISG15 transcript and protein decreased, which conferred on A549-CUG2 cell susceptibility to VSV infection. Finally, we found that overloading of H₂O₂ sensitized control A549-CUG2 cells to VSV-induced apoptosis. Taken together, these results indicate that autophagy impairment induces excessive ROS formation, which decreases S6 kinase activity and ISG15 expression, ultimately rendering the A549-CUG2 cells susceptible to VSV infection. We propose that autophagy impairment is a potential strategy for successful VSV virotherapy of CUG2-overexpressing tumors.

Darb-Esfahani S, Sinn BV, Rudl M, et al.
Interferon-stimulated gene, 15 kDa (ISG15) in ovarian high-grade serous carcinoma: prognostic impact and link to NF-κB pathway.
Int J Gynecol Pathol. 2014; 33(1):16-22 [PubMed] Related Publications
The ubiquitin-like protein interferon-stimulated gene, 15 kDa (ISG15) plays an ambiguous role in the progression and response to chemotherapy of solid cancers. We aimed to investigate the prognostic impact of ISG15 and its link to the nuclear factor κB pathway in ovarian high-grade serous carcinoma. Immunohistochemistry was performed in a cohort of 128 primary ovarian high-grade serous carcinomas treated with standard surgery and adjuvant chemotherapy using tissue microarrays. In addition, 28 matched relapsed carcinomas were investigated. ISG15 protein expression was significantly increased in relapsed carcinomas as compared to primary tumors (P=0.027). In primary carcinoma, ISG15 was positively associated with total inhibitor of κB α (IκBα) (P=0.001) as well as nuclear and cytoplasmic phospho-IκBα (p-IκBα) expression (P=0.039 and P=0.002, respectively). Patients with ISG15-positive carcinomas had a significantly longer overall survival in univariate analysis (P=0.002), and in multivariate analysis [hazard ratio=0.35 (95% confidence interval, 0.14-0.84, P=0.019)]. ISG15 is a potential prognostic marker in high-grade serous carcinoma of the ovary. Its impact on survival might be explained by its tight link to the nuclear factor κB pathway, and the further evaluation of the interplay between ISGylation machinery and nuclear factor κB, particularly with regard to response to chemotherapy, would be desirable.

Yeh YH, Yang YC, Hsieh MY, et al.
A negative feedback of the HIF-1α pathway via interferon-stimulated gene 15 and ISGylation.
Clin Cancer Res. 2013; 19(21):5927-39 [PubMed] Related Publications
PURPOSE: The IFN-stimulated gene 15 (ISG15)- and ubiquitin-conjugation pathways play roles in mediating hypoxic and inflammatory responses. To identify interaction(s) between these two tumor microenvironments, we investigated the effect of ISG15 on the activity of the master hypoxic transcription factor HIF-1α.
EXPERIMENTAL DESIGN: IFN and desferoxamine treatments were used to induce the expression of ISGs and HIF-1α, respectively. Interactions between HIF-1α and the ISG15 and ISGylation system were studied using knockdown of mRNA expression, immunoblotting, coimmunoprecipitation, and pull-down analyses. Effects of the ISG15 and ISGylation system on the HIF-1α-directed processes were examined using reporter, reverse transcription polymerase chain reaction (RT-PCR), and tumorigenic growth assays.
RESULTS: We found that the level of the free form of HIF-1α is differentially regulated by IFN treatment, and that the free ISG15 level is lower under hypoxia. Mechanism-directed studies have shown that HIF-1α not only interacts physically with ISG15, but is also ISGylated in multiple domains. ISG15 expression disrupts the functional dimerization of HIF-1α and -1β. Subsequently, expression of the ISG15 and/or ISGylation system attenuates HIF-1α-mediated gene expression and tumorigenic growth.
CONCLUSION: In summary, our results revealed cross-talk between inflammatory and hypoxic pathways through the ISGylation of HIF-1α. On the basis of these results, we propose a novel negative feedback loop for the HIF-1α-mediated pathway involving the regulation of HIF-1α via IFN-induced ISGylation.

Wan XX, Chen HC, Khan MA, et al.
ISG15 inhibits IFN-α-resistant liver cancer cell growth.
Biomed Res Int. 2013; 2013:570909 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
Hepatocellular carcinoma (HCC) is one of the most prevalent tumors worldwide. Interferon-α (IFN-α) has been widely used in the treatment of HCC, but patients eventually develop resistance. ISG15 ubiquitin-like modifier (ISG15) is a ubiquitin-like protein transcriptionally regulated by IFN-α which shows antivirus and antitumor activities. However, the exact role of ISG15 is unknown. In the present study, we showed that IFN-α significantly induced ISG15 expression but failed to induce HepG2 cell apoptosis, whereas transient overexpression of ISG15 dramatically increased HepG2 cell apoptosis. ISG15 overexpression increased overall protein ubiquitination, which was not observed in cells with IFN-α-induced ISG15 expression, suggesting that IFN-α treatment not only induced the expression of ISG15 but also inhibited ISG15-mediated ubiquitination. The tumor suppressor p53 and p21 proteins are the key regulators of cell survival and death in response to stress signals such as DNA damage. We showed that p53 or p21 is only up regulated in HepG2 cells ectopically expressing ISG15, but not in the presence of IFN-α-induced ISG15. Our results suggest that ISG15 overexpression could be developed into a powerful gene-therapeutic tool for treating IFN-α-resistant HCC.

Powell SF, Beitinjaneh A, Tessema M, et al.
Phase II study of topotecan and bevacizumab in advanced, refractory non--small-cell lung cancer.
Clin Lung Cancer. 2013; 14(5):495-501 [PubMed] Related Publications
BACKGROUND: This clinical trial evaluated whether topotecan in combination with bevacizumab improved progression-free survival (PFS) in patients with advanced, refractory non--small-cell lung cancer in a second-line setting.
PATIENT AND METHODS: Patients aged 18 years old and older received topotecan (4.0 mg/m(2)) on days 1, 8, and 15, and bevacizumab (10 mg/kg) on days 1 and 15 as intravenous infusions on a 28-day treatment cycle. Available tumor specimens were analyzed for ISG15 gene expression as a biomarker of response to topotecan.
RESULTS: Forty-two patients were enrolled in the study, with a median age of 62.5 years and a median of 3 (range, 1-7) prior treatment regimens. Almost half (n = 18, 42.9%) of the patients received prior bevacizumab therapy. PFS was 5.1 months (95% CI, 3.7-7.8 months), and overall survival was 11.5 months (95% CI, 6.8-15.5 months). Response rates were as follows: 14.3% partial response, 54.8% stable disease, and 28.6% progressive disease. Hematologic toxicities included grade 3 thrombocytopenia (n = 7, 16.7%), neutropenia (n = 4, 9.5%), and anemia (n = 2, 4.8%). One toxic death occurred due to pulmonary hemorrhage, and one patient experienced a grade 4 pulmonary embolism. Grade 3 nonhematologic adverse events were uncommon (< 8%). There was a trend for improved median PFS, 3.5 months vs. 1.8 months (P = .26), in patients with high ISG15 expression.
CONCLUSION: Bevacizumab in combination with topotecan as a salvage therapy for metastatic non--small-cell lung cancer is well tolerated and is worthy of further investigation.

Busse A, Rapion J, Fusi A, et al.
Analysis of surrogate gene expression markers in peripheral blood of melanoma patients to predict treatment outcome of adjuvant pegylated interferon alpha 2b (EORTC 18991 side study).
Cancer Immunol Immunother. 2013; 62(7):1223-33 [PubMed] Related Publications
We analysed mRNA levels of interferon response genes (ISG15, STAT1, CXCL10) of inhibitors of the JAK/STAT pathway (STAT3, SOCS1, SOCS3) and of cytokines (TNFα, IL10, TGFß1) in peripheral blood of 91 stage III melanoma patients enrolled in EORTC 18991 trial to find biomarkers indicative for disease stage and predictive for efficacy of pegylated interferon alpha-2b (PEG-IFNα-2b) therapy. mRNA levels were analysed at baseline and after 6 months. Univariate and multivariate analyses were performed to estimate the prognostic and predictive role of mRNA levels for distant metastasis-free survival (DMFS) and relapse-free survival (RFS). Compared to healthy controls, melanoma patients showed significantly higher TGFβ1 mRNA levels. In a multivariate model, increasing SOCS1 and SOCS3 mRNA levels were associated with worse RFS (P = 0.02 and P = 0.04, respectively) and DMFS (P = 0.05 and P = 0.05, respectively) due to negative correlation between, respectively, SOCS1/SOCS3 mRNA levels and ulceration or Breslow thickness. No impact of PEG-IFNα-2b on mRNA levels was observed except for ISG15 mRNA levels, which decreased in the treatment arm (P = 0.001). It seems that patients with a decrease >60 % of ISG15 mRNA levels during 6 months PEG-IFNα-2b had inferior outcome.

Laljee RP, Muddaiah S, Salagundi B, et al.
Interferon stimulated gene-ISG15 is a potential diagnostic biomarker in oral squamous cell carcinomas.
Asian Pac J Cancer Prev. 2013; 14(2):1147-50 [PubMed] Related Publications
BACKGROUND: Cancer diagnostic biomarkers have a wide range of applications that include early detection of oral precancerous lesions and oral squamous cell carcinomas, and assessing the metastatic status of lesions. The interferon stimulated ISG15 gene encodes an ubiquitin-like protein, which conjugates to stabilize activation status of associated proteins. Hence a deregulated expression of ISG15 may promote carcinogenesis. Indeed overexpression of ISG15 has been observed in several cancers and hence it has been proposed as a strong candidate cancer diagnostic biomarker. Given the emerging relationship between malignant transformation and ISG15, we sought to examine the expression pattern of this gene in tumor biopsies of oral squamous cell carcinoma (OSCC) tissues collected from Indian patients.
MATERIALS AND METHODS: Total RNA isolated from thirty oral squamous cell carcinoma tissue biopsy samples were subjected to semi-quantitative RT-PCR with ISG15 specific primers to elucidate the expression level.
RESULTS: Of the thirty oral squamous cell carcinomas that were analyzed, ISG15 expression was found in twenty four samples (80%). Twelve samples expressed low level of ISG15, six of them expressed moderately, while the rest of them expressed very high level of ISG15.
CONCLUSIONS: To the best of our knowledge, the results show for the first time an overexpression of ISG15 in up to 80% of oral squamous cell carcinoma tissues collected from Indian patients. Hence ISG15 may be explored for the possibility of use as a high confidence diagnostic biomarker in oral cancers.

Shen J, Wei J, Wang H, et al.
A three-gene signature as potential predictive biomarker for irinotecan sensitivity in gastric cancer.
J Transl Med. 2013; 11:73 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
OBJECTIVE: Personalized chemotherapy based on molecular biomarkers can maximize anticancer efficiency. We aim to investigate predictive biomarkers capable of predicting response to irinotecan-based treatment in gastric cancer.
METHODS: We examined gene expression of APTX, BRCA1, ERCC1, ISG15, Topo1 and methylation of SULF2 in formalin-fixed paraffin-embedded gastric cancer tissues from 175 patients and evaluated the association between gene expression levels or methylation status and in vitro sensitivity to irinotecan. We used multiple linear regression analysis to develop a gene-expression model to predict irinotecan sensitivity in gastric cancer and validated this model in vitro and vivo.
RESULTS: Gene expression levels of APTX, BRCA1 and ERCC1 were significantly lower in irinotecan-sensitive gastric cancer samples than those irinotecan-resistant samples (P<0.001 for all genes), while ISG15 (P=0.047) and Topo1 (P=0.002) were significantly higher. Based on those genes, a three-gene signature were established, which was calculated as follows: Index =0.488 - 0.020× expression level of APTX + 0.015× expression level of Topo1 - 0.011 × expression level of BRCA1. The three-gene signature was significantly associated with irinotecan sensitivity (rho=0.71, P<0.001). The sensitivity and specificity for the prediction of irinotecan sensitivity based on the three-gene signature reached 73% and 86%, respectively. In another independent testing set, the irinotecan inhibition rates in gastric samples with sensitive-signature were much higher than those with resistant-signature (65% vs. 22%, P<0.001). Irinotecan therapy with 20 mg/kg per week to immunodeficient mice carrying xenografts with sensitive-signature dramatically arrested the growth of tumors (P<0.001), but had no effect on mice carrying xenografts with resistant-signature.
CONCLUSIONS: The three-gene signature established herein is a potential predictive biomarker for irinotecan sensitivity in gastric cancer.

Burks J, Reed RE, Desai SD
ISGylation governs the oncogenic function of Ki-Ras in breast cancer.
Oncogene. 2014; 33(6):794-803 [PubMed] Related Publications
Aberrant expression of the oncogenic Kirsten-Ras (Ki-Ras) and interferon-stimulated gene 15 (ISG15) pathways is common in breast and other cancers. However, whether these dysregulated pathways cooperate to promote malignancy is not known. This study links Ki-Ras and ISG15 in a previously unidentified regulatory loop that may underlie malignant transformation of mammary cells. We show that oncogenic Ki-Ras regulates the expression of the ISG15 pathway (free ISG15 and ISG15 conjugates), and ISG15, in turn, stabilizes Ki-Ras protein by inhibiting its targeted degradation via lysosomes in breast cancer cells. Disruption of this loop by silencing either Ki-Ras or the ISG15 pathway restored the disrupted cellular architecture, a hallmark feature of most cancer cells. We also demonstrate that ISG15 and UbcH8 (ISG15-specific conjugating enzyme) shRNAs reversed Ki-Ras mutation-associated phenotypes of cancer cells, such as increased cell proliferation, colony formation, anchorage-independent growth in soft agar, cell migration, and epithelial-mesenchymal transition. As UbcH8-silenced breast cancer cells are devoid of ISG15 conjugates but have free ISG15, our results using UbcH8-silenced cells suggest that ISG15 conjugates, and not free ISG15, contributes to oncogenic Ki-Ras transformation. We have thus identified the conjugated form of ISG15 as a critical downstream mediator of oncogenic Ki-Ras, providing a potential mechanistic link between ISG15 and Ki-Ras-mediated breast tumorigenesis. Our findings, which show that inhibition of the ISGylation reverses the malignant phenotypes of breast cancer cells expressing oncogenic Ki-Ras, support the development of ISG15 conjugation inhibitors for treating breast and also other cancers expressing oncogenic Ki-Ras.

Sgorbissa A, Brancolini C
IFNs, ISGylation and cancer: Cui prodest?
Cytokine Growth Factor Rev. 2012; 23(6):307-14 [PubMed] Related Publications
IFNs are cytokines that segregate viral infections, modulate the immune responses and influence tumor cells survival. These options are under the control of ISGs (Interferon Stimulated Genes) which expression is propelled by IFNs. To the ISGs family belong all the components of the molecular machinery that modifies proteins by the addition of the ubiquitin-like protein ISG15, in a process known as ISGylation. Despite alterations in the components of this machinery are frequently observed in cancer, the contribution of ISG15 and of ISGylation to tumor growth and resistance to chemotherapy is unclear and debated. With the aim of elucidating this point, in this review we have discussed about recent data pointing to a dysregulation of the IFN signaling and the ISGylation system in cancer.

Guo Y, Chinyengetere F, Dolinko AV, et al.
Evidence for the ubiquitin protease UBP43 as an antineoplastic target.
Mol Cancer Ther. 2012; 11(9):1968-77 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
New pharmacologic targets are needed for lung cancer. One candidate pathway to target is composed of the E1-like ubiquitin-activating enzyme (UBE1L) that associates with interferon-stimulated gene 15 (ISG15), which complexes with and destabilizes cyclin D1. Ubiquitin protease 43 (UBP43/USP18) removes ISG15 from conjugated proteins. This study reports that gain of UBP43 stabilized cyclin D1, but not other D-type cyclins or cyclin E. This depended on UBP43 enzymatic activity; an enzymatically inactive UBP43 did not affect cyclin D1 stability. As expected, small interfering RNAs that reduced UBP43 expression also decreased cyclin D1 levels and increased apoptosis in a panel of lung cancer cell lines. Forced cyclin D1 expression rescued UBP43 apoptotic effects, which highlighted the importance of cyclin D1 in conferring this. Short hairpin RNA-mediated reduction of UBP43 significantly increased apoptosis and reduced murine lung cancer growth in vitro and in vivo after transplantation of these cells into syngeneic mice. These cells also exhibited increased response to all-trans-retinoic acid, interferon, or cisplatin treatments. Notably, gain of UBP43 expression antagonized these effects. Normal-malignant human lung tissue arrays were examined independently for UBP43, cyclin D1, and cyclin E immunohistochemical expression. UBP43 was significantly (P < 0.01) increased in the malignant versus normal lung. A direct relationship was found between UBP43 and cyclin D1 (but not cyclin E) expression. Differential UBP43 expression was independently detected in a normal-malignant tissue array with diverse human cancers. Taken together, these findings uncovered UBP43 as a previously unrecognized antineoplastic target.

Sumino J, Uzawa N, Okada N, et al.
Gene expression changes in initiation and progression of oral squamous cell carcinomas revealed by laser microdissection and oligonucleotide microarray analysis.
Int J Cancer. 2013; 132(3):540-8 [PubMed] Related Publications
Oral carcinogenesis is a complex process involving multiple genes. However, the genetic changes involved in this process are not apparent in identical oral squamous cell carcinomas (OSCCs). According to pathological characteristics, samples of normal tissue, oral dysplastic lesions (ODLs), and invasive cancers were obtained from identical OSCCs using laser microdissection (LMD). Large-scale gene expression profiling was carried out on 33 samples derived from 11 OSCCs. We analyzed genes differentially expressed in normal tissues vs. ODLs and in ODLs vs. invasive tumors and identified 15 candidate genes with continuously increasing or decreasing expression during oral carcinogenesis. One of these genes, ISG15, was chosen for further characterization. Real-time quantitative reverse transcription-polymerase chain reaction and immunohistochemical analysis confirmed that ISG15 expression consistently increased during oral tumorigenesis. An ISG15 high-expression level was significantly associated with poor prognosis (p = 0.027). In addition, patients with high-expression tumors had a poorer 5-year survival rate than patients with low expression levels (p = 0.019). In conclusion, we identified 15 genes with continuously increasing or decreasing expression during oral carcinogenesis. One of these, ISG15, is likely to be associated with both dysgenesis and tumorigenesis and may be a potential prognostic marker for oral cancer.

Du Z, Whitt MA, Baumann J, et al.
Inhibition of type I interferon-mediated antiviral action in human glioma cells by the IKK inhibitors BMS-345541 and TPCA-1.
J Interferon Cytokine Res. 2012; 32(8):368-77 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
The nuclear factor-kappa B (NFκB) signal transduction pathway plays an important role in immunity, inflammation, cell growth, and survival. Since dysregulation of this pathway results in high, constitutive NFκB activation in various cancers and immune disorders, the development of specific drugs to target this pathway has become a focus for treating these diseases. NFκB regulates various aspects of the cellular response to interferon (IFN). However, the role of the upstream regulator of the NFκB signaling pathway, the inhibitor of κB kinase (IKK) complex, on IFN function has not been examined. In the present study, we examined the effects of 2 IKK inhibitors, N-(1,8-Dimethylimidazo[1,2-a]quinoxalin-4-yl)-1,2-ethanediamine hydrochloride (BMS-345541) and 2-[(aminocarbonyl)amino]-5-(4-fluorophenyl)-3-thiophenecarboxamide (TPCA-1), on IFN action in several human glioma cell lines. IKK inhibitors inhibit glioma cell proliferation, as well as TNF-induced RelA (p65) nuclear translocation and NFκB-dependent IL8 gene expression. Importantly, BMS-345541 and TPCA-1 differentially inhibit IFN-induced gene expression, completely suppressing MX1 and GBP1 gene expression, while having only a minor effect on ISG15 expression. Furthermore, these IKK inhibitors displayed marked differences in blocking IFN-induced antiviral action against cytopathic effects and replication of vesicular stomatitis virus (VSV) and encephalomyocarditis virus (EMCV). Our results show that the IKK complex plays an important function in IFN-induced gene expression and antiviral activity. Since VSV and EMCV are oncolytic viruses used in cancer therapy, our results indicate the potential synergy in combining IKK inhibitors with oncolytic viruses.

Chu ZH, Liu L, Zheng CX, et al.
Proteomic analysis identifies translationally controlled tumor protein as a mediator of phosphatase of regenerating liver-3-promoted proliferation, migration and invasion in human colon cancer cells.
Chin Med J (Engl). 2011; 124(22):3778-85 [PubMed] Related Publications
BACKGROUND: Considerable evidence suggests that phosphatase of regenerating liver-3 (PRL-3) plays multiple roles in cancer metastasis; however, the molecular mechanisms remain largely unknown. The aim of this study was to identify proteins associated with PRL-3-promoted colon cancer metastasis, by comparative proteomic analysis.
METHODS: Proteomes of human colon cancer LoVo cells transfected with PRL-3 gene (LoVo-PRL-3) or empty vector PAcGFP-C3 (LoVo-control) were compared using 2D gel electrophoresis. Proteins that varied significantly in concentration were selected and identified using mass spectrometry. Expression of translationally controlled tumor protein (TCTP) mRNA and protein in LoVo-PRL-3 and LoVo-control cells was detected by real-time PCR and Western blotting. Small interfering RNA (siRNA) targeting TCTP was used for silencing TCTP expression in LoVo-PRL-3 cells. Functional significance of TCTP in PRL-3-promoted colon cancer cell proliferation, migration and invasion was investigated by Cell Counting Kit-8 assay and transwell chamber.
RESULTS: Seventeen proteins displaying significant and reproducible differences between LoVo-PRL-3 and LoVo-control cells were identified. Ten proteins were upregulated and seven were downregulated in LoVo-PRL-3 cells when compared with LoVo-control cells. Eight identified proteins are associated with distinct steps of tumor metastasis: ubiquitin-like protein ISG15, interleukin-18, TCTP, serpin B5, annexin A3, macrophage-capping protein, ATP-dependent RNA helicase DDX3X, and cathepsin D. Real-time PCR and Western blotting results showed that both TCTP mRNA and protein were significantly increased in LoVo-PRL-3 cells compared to LoVo-control cells. Transfection with TCTP siRNA significantly reduced the expression of both mRNA and protein levels of TCTP in LoVo-PRL-3 cells. Knockdown of TCTP by siRNA inhibited PRL-3-promoted proliferation, migration and invasion of LoVo-PRL-3 cells.
CONCLUSION: Our results imply that TCTP might be a mediator of PRL-3-promoted proliferation, migration and invasion of human colon cancer cells.

Vincent-Chong VK, Ismail SM, Rahman ZA, et al.
Genome-wide analysis of oral squamous cell carcinomas revealed over expression of ISG15, Nestin and WNT11.
Oral Dis. 2012; 18(5):469-76 [PubMed] Related Publications
BACKGROUND: Multistep pathways and mechanisms are involved in the development of oral cancer. Chromosomal alterations are one of such key mechanisms implicated oral carcinogenesis. Therefore, this study aims to determine the genomic copy number alterations (CNAs) in oral squamous cell carcinoma (OSCC) using array comparative genomic hybridization (aCGH) and in addition attempt to correlate CNAs with modified gene expression.
MATERIALS AND METHODS: Genome-wide screening was performed on 15 OSCCs using high-density aCGH. On the basis of pathway analysis, three genes (ISG15, Nestin and WNT11) which mapped to CNA regions were selected for further evaluation of their mRNA expression using quantitative reverse transcriptase PCR (qRT-PCR).
RESULTS: Copy number alterations were observed on multiple genomic regions, including amplifications on 1p, 3q, 5p, 6p, 7p, 8q, 9q, 11q, 12q, 16p, 18p and deletions on 3p, 7q, 8p, 11q, 19q and 20q. Among the three selected genes, ISG15 had the highest mRNA expression level with a 22.5-fold increase, followed by Nestin with a 4.5-fold increase and WNT11 with a 2.5-fold increase.
CONCLUSIONS: This study has identified several major CNAs in oral cancer genomes and indicated that this correlates with over expression of the ISG15, WNT11, and Nestin genes.

Desai SD, Reed RE, Burks J, et al.
ISG15 disrupts cytoskeletal architecture and promotes motility in human breast cancer cells.
Exp Biol Med (Maywood). 2012; 237(1):38-49 [PubMed] Related Publications
The interferon-stimulated gene 15 (ISG15) pathway is highly elevated in breast cancer; however, very little is known about how the ISG15 pathway contributes to breast tumorigenesis. In the current study, using the gene disruption approach, we demonstrate that both ISG15 and UbcH8 (ISG15-specific conjugating enzyme) disrupt F-actin architecture and formation of focal adhesions in ZR-75-1 breast cancer cells. In addition, ISG15 and UbcH8 promote breast cancer cell migration. We also demonstrate that ISG15 inhibits ubiquitin/26S proteasome-mediated turnover of proteins implicated in tumor cell motility, invasion and metastasis. Together, our results suggest that the aberrant activation of the ISG15 pathway confers a motile phenotype to breast cancer cells by disrupting cell architecture and stabilizing proteins involved in cell motility, invasion and metastasis. Because the cellular architecture is conserved and the ISG15 pathway is constitutively activated in tumor cells of different lineages, it is reasonable to assume that our observations in breast cancer must hold true for many other tumors.

Tessema M, Yingling CM, Thomas CL, et al.
SULF2 methylation is prognostic for lung cancer survival and increases sensitivity to topoisomerase-I inhibitors via induction of ISG15.
Oncogene. 2012; 31(37):4107-16 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
The heparan sulfate 6-O-endosulfatase (SULF2) promotes growth and metastasis of solid tumors. We recently identified that cytosine methylation of the SULF2 promoter is associated with better survival of resected lung adenocarcinoma patients, and now also demonstrates a marginal improvement in survival of advanced non-small cell lung cancer (NSCLC) patients receiving standard chemotherapy (hazard ratio=0.63, P=0.07). Subsequent studies focused on investigating the effect of methylation on SULF2 expression and its genome-wide impact. The genes and pathways modulated by epigenetic inactivation of SULF2 and the effects on sensitivity to chemotherapy were characterized in vitro and in vivo. Silencing SULF2 through small interfering RNA or methylation primarily increased expression of interferon-inducible genes including ISG15, a marker for increased sensitivity to topoisomerase-1 inhibitors such as camptothecin (CPT). NSCLC cell lines with methylated SULF2 (SULF2M) express 60-fold higher ISG15 compared with SULF2 unmethylated (SULF2U) NSCLC cell lines and normal human bronchial epithelial cells. In vitro, SULF2M and high ISG15 (ISG15H)-expressing NSCLC cell lines were 134-fold more sensitive to CPT than SULF2U and low ISG15 (ISG15L)-expressing cell lines. Topotecan, a soluble analog of CPT and FDA-approved anticancer drug, dramatically arrested the growth of SULF2M-ISG15H, but not SULF2U-ISG15L lung tumors in nude mice (P<0.002). Similarly, high ISG15 expression that is comparable to the topotecan (TPT)-sensitive NSCLC cell lines was found in tumors from 25% of NSCLC patients compared with normal lung, indicating a potential to identify and target the most sensitive NSCLC subpopulation for personalized TPT therapy.

Tsai YC, Pestka S, Wang LH, et al.
Interferon-β signaling contributes to Ras transformation.
PLoS One. 2011; 6(8):e24291 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
Increasing evidence has pointed to activated type I interferon signaling in tumors. However, the molecular basis for such activation and its role in tumorigenesis remain unclear. In the current studies, we report that activation of type I interferon (IFN) signaling in tumor cells is primarily due to elevated secretion of the type I interferon, IFN-β. Studies in oncogene-transformed cells suggest that oncogenes such as Ras and Src can activate IFN-β signaling. Significantly, elevated IFN-β signaling in Ras-transformed mammary epithelial MCF-10A cells was shown to contribute to Ras transformation as evidenced by morphological changes, anchorage-independent growth, and migratory properties. Our results demonstrate for the first time that the type I IFN, IFN-β, contributes to Ras transformation and support the notion that oncogene-induced cytokines play important roles in oncogene transformation.

Lee J, Li L, Gretz N, et al.
Absent in Melanoma 2 (AIM2) is an important mediator of interferon-dependent and -independent HLA-DRA and HLA-DRB gene expression in colorectal cancers.
Oncogene. 2012; 31(10):1242-53 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
Absent in Melanoma 2 (AIM2) is a member of the HIN-200 family of hematopoietic, IFN-inducible, nuclear proteins, associated with both, infection defense and tumor pathology. Recently, AIM2 was found to act as a DNA sensor in innate immunity. In addition, we and others have previously demonstrated a high frequency of AIM2-alterations in microsatellite unstable (MSI-H) tumors. To further elucidate AIM2 function in colorectal tumors, we here addressed AIM2-responsive target genes by microarray based gene expression profiling of 22 244 human genes. A total of 111 transcripts were significantly upregulated, whereas 80 transcripts turned out to be significantly downregulated in HCT116 cells, constitutively expressing AIM2, compared with AIM2-negative cells. Among the upregulated genes that were validated by quantitative PCR and western blotting we recognized several interferon-stimulated genes (ISGs: IFIT1, IFIT2, IFIT3, IFI6, IRF7, ISG15, HLA-DRA, HLA-DRB, TLR3 and CIITA), as well as genes involved in intercellular adhesion and matrix remodeling. Expression of ISGs correlated with expression of AIM2 in 10 different IFN-γ treated colorectal cancer cell lines. Moreover, small interfering RNA-mediated knock-down of AIM2 resulted in reduced expression of HLA-DRA, HLA-DRB and CIITA in IFN-γ-treated cells. IFN-γ independent induction of HLA-DR genes and their encoded proteins was also demonstrated upon doxycyclin-regulated transient induction of AIM2. Luciferase reporter assays revealed induction of the HLA-DR promoter upon AIM2 transfection in different cell lines. STAT-signaling was not involved in IFN-γ independent induction of ISGs, arguing against participation of cytokines released in an autostimulating manner. Our data indicate that AIM2 mediates both IFN-γ dependent and independent induction of several ISGs, including genes encoding the major histocompatibility complex (MHC) class II antigens HLA-DR-α and -β. This suggests a novel role of the IFN/AIM2/ISG cascade likewise in cancer cells.

Rajkumar T, Sabitha K, Vijayalakshmi N, et al.
Identification and validation of genes involved in cervical tumourigenesis.
BMC Cancer. 2011; 11:80 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
BACKGROUND: Cervical cancer is the most common cancer among Indian women. This cancer has well defined pre-cancerous stages and evolves over 10-15 years or more. This study was undertaken to identify differentially expressed genes between normal, dysplastic and invasive cervical cancer.
MATERIALS AND METHODS: A total of 28 invasive cervical cancers, 4 CIN3/CIS, 4 CIN1/CIN2 and 5 Normal cervix samples were studied. We have used microarray technique followed by validation of the significant genes by relative quantitation using Taqman Low Density Array Real Time PCR. Immunohistochemistry was used to study the protein expression of MMP3, UBE2C and p16 in normal, dysplasia and cancers of the cervix. The effect of a dominant negative UBE2C on the growth of the SiHa cells was assessed using a MTT assay.
RESULTS: Our study, for the first time, has identified 20 genes to be up-regulated and 14 down-regulated in cervical cancers and 5 up-regulated in CIN3. In addition, 26 genes identified by other studies, as to playing a role in cervical cancer, were also confirmed in our study. UBE2C, CCNB1, CCNB2, PLOD2, NUP210, MELK, CDC20 genes were overexpressed in tumours and in CIN3/CIS relative to both Normal and CIN1/CIN2, suggesting that they could have a role to play in the early phase of tumorigenesis. IL8, INDO, ISG15, ISG20, AGRN, DTXL, MMP1, MMP3, CCL18, TOP2A AND STAT1 were found to be upregulated in tumours. Using Immunohistochemistry, we showed over-expression of MMP3, UBE2C and p16 in cancers compared to normal cervical epithelium and varying grades of dysplasia. A dominant negative UBE2C was found to produce growth inhibition in SiHa cells, which over-expresses UBE2C 4 fold more than HEK293 cells.
CONCLUSIONS: Several novel genes were found to be differentially expressed in cervical cancer. MMP3, UBE2C and p16 protein overexpression in cervical cancers was confirmed by immunohistochemistry. These will need to be validated further in a larger series of samples. UBE2C could be evaluated further to assess its potential as a therapeutic target in cervical cancer.

Watson IR, Irwin MS, Ohh M
NEDD8 pathways in cancer, Sine Quibus Non.
Cancer Cell. 2011; 19(2):168-76 [PubMed] Related Publications
There are 17 known ubiquitin-like proteins (UBLs) from nine phylogenetically distinct classes (NEDD8, SUMO, ISG15, FUB1, FAT10, Atg8, Atg12, Urm1, and UFM1) that have been identified to conjugate to substrates in a manner analogous to ubiquitin. NEDD8 is one of the most studied UBLs and shares the highest amino acid similarity to ubiquitin. Here, we review the current knowledge of the NEDD8 conjugation cascade derived from functional studies in genetic model organisms, structural insights from crystallographic studies, biochemical studies identifying a growing list of NEDD8 substrates with oncogenic implications, and attempts to pharmacologically target the NEDD8 pathway in cancer.

Akutsu M, Ye Y, Virdee S, et al.
Molecular basis for ubiquitin and ISG15 cross-reactivity in viral ovarian tumor domains.
Proc Natl Acad Sci U S A. 2011; 108(6):2228-33 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
Crimean Congo hemorrhagic fever virus (CCHFV) is a deadly human pathogen that evades innate immune responses by efficiently interfering with antiviral signaling pathways mediated by NF-κB, IRF3, and IFNα/β. These pathways rely on protein ubiquitination for their activation, and one outcome is the modification of proteins with the ubiquitin (Ub)-like modifier interferon-stimulated gene (ISG)15. CCHFV and related viruses encode a deubiquitinase (DUB) of the ovarian tumor (OTU) family, which unlike eukaryotic OTU DUBs also targets ISG15 modifications. Here we characterized the viral OTU domain of CCHFV (vOTU) biochemically and structurally, revealing that it hydrolyzes four out of six tested Ub linkages, but lacks activity against linear and K29-linked Ub chains. vOTU cleaved Ub and ISG15 with similar kinetics, and we were able to understand vOTU cross-reactivity at the molecular level from crystal structures of vOTU in complex with Ub and ISG15. An N-terminal extension in vOTU not present in eukaryotic OTU binds to the hydrophobic Ile44 patch of Ub, which results in a dramatically different Ub orientation compared to a eukaryotic OTU-Ub complex. The C-terminal Ub-like fold of ISG15 (ISG15-C) adopts an equivalent binding orientation. Interestingly, ISG15-C contains an additional second hydrophobic surface that is specifically contacted by vOTU. These subtle differences in Ub/ISG15 binding allowed the design of vOTU variants specific for either Ub or ISG15, which will be useful tools to understand the relative contribution of ubiquitination vs. ISGylation in viral infection. Furthermore, the crystal structures will allow structure-based design of antiviral agents targeting this enzyme.

James TW, Frias-Staheli N, Bacik JP, et al.
Structural basis for the removal of ubiquitin and interferon-stimulated gene 15 by a viral ovarian tumor domain-containing protease.
Proc Natl Acad Sci U S A. 2011; 108(6):2222-7 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
The attachment of ubiquitin (Ub) and the Ub-like (Ubl) molecule interferon-stimulated gene 15 (ISG15) to cellular proteins mediates important innate antiviral responses. Ovarian tumor (OTU) domain proteases from nairoviruses and arteriviruses were recently found to remove these molecules from host proteins, which inhibits Ub and ISG15-dependent antiviral pathways. This contrasts with the Ub-specific activity of known eukaryotic OTU-domain proteases. Here we describe crystal structures of a viral OTU domain from the highly pathogenic Crimean-Congo haemorrhagic fever virus (CCHFV) bound to Ub and to ISG15 at 2.5-Å and 2.3-Å resolution, respectively. The complexes provide a unique structural example of ISG15 bound to another protein and reveal the molecular mechanism of an ISG15 cross-reactive deubiquitinase. To accommodate structural differences between Ub and ISG15, the viral protease binds the β-grasp folds of Ub and C-terminal Ub-like domain of ISG15 in an orientation that is rotated nearly 75° with respect to that observed for Ub bound to a representative eukaryotic OTU domain from yeast. Distinct structural determinants necessary for binding either substrate were identified and allowed the reengineering of the viral OTU protease into enzymes with increased substrate specificity, either for Ub or for ISG15. Our findings now provide the basis to determine in vivo the relative contributions of deubiquitination and deISGylation to viral immune evasion tactics, and a structural template of a promiscuous deubiquitinase from a haemorrhagic fever virus that can be targeted for inhibition using small-molecule-based strategies.

Englert NA, Spink BC, Spink DC
Persistent and non-persistent changes in gene expression result from long-term estrogen exposure of MCF-7 breast cancer cells.
J Steroid Biochem Mol Biol. 2011; 123(3-5):140-50 [PubMed] Related Publications
Life-long estrogen exposure is recognized as a major risk factor for the development of breast cancer. While the initial events in the regulation of gene expression by estrogen have been described in detail, far less is known of the role of estrogen in the long-term regulation of gene expression. In this study, we investigated the effects of long-term exposure of MCF-7 breast cancer cells to 1nM 17β-estradiol on gene expression with the goal of distinguishing between gene expression that is continually reliant on estrogen receptor (ER) function as opposed to secondary and persistent effects that are downstream of ER. To assess the direct involvement of ER in the differential gene expression of long-term estrogen exposed (LTEE) cells in comparison with that of control cells, we exposed cultures to the selective estrogen receptor modulator raloxifene (RAL). cDNA microarray analysis showed that exposure to RAL inhibited expression of numerous characterized estrogen-regulated genes, including PGR, GREB1, and PDZK1. Genes that were increased in expression in LTEE cells yet were unaffected by RAL exposure included the aryl hydrocarbon receptor (AHR) and numerous other genes that were not previously reported to be regulated by estrogen. Epigenetic regulation was evident for the AHR gene; AhR transcript levels remained elevated for several cell passages after the removal of estrogen. Signal transducer and activator of transcription 1 (STAT1); STAT1-regulated genes including ISG15, IFI27, and IFIT1; and MHC class I genes were also up-regulated in LTEE cells and were unaffected by RAL exposure. STAT1 is commonly overexpressed in breast and other cancers, and is associated with increased resistance to radiation and chemotherapy. This is the first study to relate estrogen exposure to increased STAT1 expression in breast cancer cells, an effect that may represent an additional role of estrogen in the pathogenesis of breast cancer.

Guo Y, Dolinko AV, Chinyengetere F, et al.
Blockade of the ubiquitin protease UBP43 destabilizes transcription factor PML/RARα and inhibits the growth of acute promyelocytic leukemia.
Cancer Res. 2010; 70(23):9875-85 [PubMed] Article available free on PMC after 01/09/2015 Related Publications
More effective treatments for acute promyelocytic leukemia (APL) are needed. APL cell treatment with all-trans-retinoic acid (RA) degrades the chimeric, dominant-negative-acting transcription factor promyelocytic leukemia gene (PML)/RARα, which is generated in APL by chromosomal translocation. The E1-like ubiquitin-activating enzyme (UBE1L) associates with interferon-stimulated gene ISG15 that binds and represses PML/RARα protein. Ubiquitin protease UBP43/USP18 removes ISG15 from conjugated proteins. In this study, we explored how RA regulates UBP43 expression and the effects of UBP43 on PML/RARα stability and APL growth, apoptosis, or differentiation. RA treatment induced UBE1L, ISG15, and UBP43 expression in RA-sensitive but not RA-resistant APL cells. Similar in vivo findings were obtained in a transgenic mouse model of transplantable APL, and in the RA response of leukemic cells harvested directly from APL patients. UBP43 knockdown repressed PML/RARα protein levels and inhibited RA-sensitive or RA-resistant cell growth by destabilizing the PML domain of PML/RARα. This inhibitory effect promoted apoptosis but did not affect the RA differentiation response in these APL cells. In contrast, elevation of UBP43 expression stabilized PML/RARα protein and inhibited apoptosis. Taken together, our findings define the ubiquitin protease UBP43 as a novel candidate drug target for APL treatment.

Jiang L, Saetre P, Radomska KJ, et al.
QKI-7 regulates expression of interferon-related genes in human astrocyte glioma cells.
PLoS One. 2010; 5(9) [PubMed] Article available free on PMC after 01/09/2015 Related Publications
BACKGROUND: The human QKI gene, called quaking homolog, KH domain RNA binding (mouse), is a candidate gene for schizophrenia encoding an RNA-binding protein. This gene was shown to be essential for myelination in oligodendrocytes. QKI is also highly expressed in astrocytes, but its function in these cells is not known.
METHODS/PRINCIPAL FINDINGS: We studied the effect of small interference RNA (siRNA)-mediated QKI depletion on global gene expression in human astrocyte glioma cells. Microarray measurements were confirmed with real-time quantitative polymerase chain reaction (qPCR). The presence of QKI binding sites (QRE) was assessed by a bioinformatic approach. Viability and cell morphology were also studied. The most significant alteration after QKI silencing was the decreased expression of genes involved in interferon (IFN) induction (P = 6.3E-10), including IFIT1, IFIT2, MX1, MX2, G1P2, G1P3, GBP1 and IFIH1. All eight genes were down-regulated after silencing of the splice variant QKI-7, but were not affected by QKI-5 silencing. Interestingly, four of them were up-regulated after treatment with the antipsychotic agent haloperidol that also resulted in increased QKI-7 mRNA levels.
CONCLUSIONS/SIGNIFICANCE: The coordinated expression of QKI-7 splice variant and IFN-related genes supports the idea that this particular splice variant has specific functions in astrocytes. Furthermore, a role of QKI-7 as a regulator of an inflammatory gene pathway in astrocytes is suggested. This hypothesis is well in line with growing experimental evidence on the role of inflammatory components in schizophrenia.

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