Human Endogenous Retrovirus Type K Research Articles

Dolutegravir Inhibits Proliferation and Motility of BT-20 Tumor Cells Through Inhibition of Human Endogenous Retrovirus Type K.

Increasing evidence points to the role of endogenous retroviruses (ERVs) in driving cancer cell proliferation. The purpose of this study was to explore the possibility of repurposing antiretroviral agents to inhibit ERVs as a new approach to cancer treatment. We found that an integrase strand-transfer inhibitor, dolutegravir (DTG), effectively inhibited the proliferation of multiple cancer cell lines and its antiproliferative potency was positively correlated with the expression levels of the human endogenous retrovirus type K (HERV-K). DTG inhibited the expression of HERV-K in multiple human cancer cell lines and the mouse mammary tumor virus (MMTV) in the murine 4T1 mammary cancer cell line. We chose the fast-growing BT-20 cell line as a model to study the in vitro antiproliferative mechanisms of DTG. BT-20 cells overexpressing both HERV-K env and pol genes became more resistant to DTG than cells transduced with vector alone. Knockdown of HERV-K also increased DTG resistance of BT-20 cells. The antiproliferative effect of DTG correlated with enhanced expression of E-cadherin and reduction in cell motility and invasiveness. Surprisingly, DTG stimulated expression of the env gene of MMTV in vivo and promoted metastasis of 4T1 tumor cells to the lungs. Taken together, our data support the role of ERVs in tumor development and encourage the further search for antiretroviral agents to treat malignancies in which ERVs are active.

Abstract 1149: Decitabine inhibits breast cancer cell proliferation through inhibition of endogenous retroviruses in vitro

Abstract The purpose of the study is to elucidate the antineoplastic mechanisms of decitabine, a DNA methyltransferase inhibitor. Previous literature suggests that decitabine activates human endogenous retroviruses which subsequently enhances expression of interferons, thereby suppressing tumor cell proliferation. Contrary to this hypothesis, our in vitro study with human and mouse breast cancer cell lines showed a positive correlation between the antiproliferative effect of decitabine and its suppressive effect on two endogenous retroviruses, the human endogenous retrovirus type K (HERV-K) and the mouse mammary tumor virus (MMTV). Decitabine stimulated proliferation of the T47D human breast cancer cell line at lower doses but inhibited cell proliferation at higher doses. Correspondingly, HERV-K transcripts (env and pol) increased at lower doses and decreased at higher doses. Interestingly, expression of the E-cadherin gene, an indicator of epithelial differentiation, followed an opposite trend. Decitabine inhibited proliferation of the mouse 4T1 breast cancer cell line and its expression of MMTV in a dose-dependent manner, while enhancing expression of the mouse E-cadherin. 4T1 cells overexpressing MMTV env became more resistant to decitabine, so was a human breast cancer cell line (BT-20) overexpressing HERV-K env, while T47D cells with HERV-K knockdown became more susceptible to the drug. Meanwhile, in vivo studies showed that decitabine successfully suppressed tumor development in BALB/c mice inoculated with 4T1 cells. Surprisingly, expression of MMTV env was elevated in tumors of mice treated with decitabine, along with enhanced E-cadherin expression. These data suggest decitabine inhibits cancer cell proliferation (at least partially) through inhibition of endogenous retroviruses in vitro, but its mechanisms of action in vivo are different. Further studies of the interaction between decitabine and endogenous retroviruses using engineered 4T1 cells in BALB/c mice are currently underway. Citation Format: Jiayi Li, John Lin, Leo Andrada, Bryce Grohol, Serratt Nong, Yingguang Liu. Decitabine inhibits breast cancer cell proliferation through inhibition of endogenous retroviruses in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1149.

Abstract 1164: Human endogenous retrovirus type K promotes proliferation of Merlin negative schwannoma and meningioma which can be inhibited by anti-retroviral and anti-TEAD drugs

Abstract Deficiency of the tumor suppressor Merlin causes the development of schwannoma, meningioma and ependymoma tumors. These can occur spontaneously or in the hereditary disease Neurofibromatosis type 2 (NF2). Merlin mutations are also relevant in a variety of other tumors. Currently available treatments are surgery or radiosurgery which are only partially effective, with tumors frequently reoccurring and in case of meningioma often as a higher grade. There is an urgent need for effective drug treatments.In this study, we investigated the role of Human Endogenous Retrovirus Type K (HERV-K) and its targetability in Merlin negative schwannoma and meningioma tumors by using tissues and primary cells isolated form patients employing immunohistochemistry, immunocytochemistry, western blotting and proliferation assays. We demonstrate that HERV-K proteins are overexpressed in Merlin negative schwannoma and all meningioma grades. Furthermore, we implicate CRL4DCAF1 and YAPT/EAD Hippo pathway in this overexpression and suggest that exosome transport of the HERV-K Envelope (Env) protein might contribute to schwannoma development. We also show that: (i) Ectopic overexpression of HERV-K Env in normal Schwann cells increased proliferation and upregulated the transcription factor c-Jun. Env overexpression also increased activity of the extracellular signal-regulated kinase 1/2 (pERK1/2), a known mitogenic pathway in schwannoma. (ii) An anti-Env monoclonal antibody decreased pERK1/2 and reduced proliferation of schwannoma cells. iii) FDA-approved retroviral protease inhibitors Ritonavir, Atazanavir and Lopinavir decreased pERK1/2 and cyclin D1 and reduced proliferation of schwannoma and grade I meningioma cells. We provide evidence for HERV-K Env contributing to the development of NF2-associated schwannomas and meningiomas. Considering the urgent need of drugs to treat NF2, we suggest the trialling of antiretroviral protease inhibitors, and consideration of anti-HERV-K Env immunotherapy, as well as TEAD-specific inhibitors in these patients. The above treatments would also be potentially beneficial for patients with other tumors caused by Merlin deficiency. Citation Format: Sylwia Ammoun, Emmanuel A. Maze, Bora Agit, Robert Belshaw, C Oliver Hanemann. Human endogenous retrovirus type K promotes proliferation of Merlin negative schwannoma and meningioma which can be inhibited by anti-retroviral and anti-TEAD drugs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1164.

Virome Capture Sequencing in Castleman Disease Identifies Associations with Herpesviridae Family Members but No Novel Viruses

Castleman disease (CD) describes multiple distinct and heterogeneous disorders defined by common lymph node histopathology, including atrophic or hyperplastic germinal centers, prominent follicular dendritic cells, hypervascularization, polyclonal lymphoproliferation, and/or polytypic plasmacytosis. Unicentric CD (UCD) involves a solitary lymph node station that displays CD histopathology, whereas multicentric CD (MCD) involves multiple regions of enlarged nodes. Most UCD patients do not experience systemic symptoms and are successfully treated by removal of the enlarged node. In contrast, MCD involves constitutional symptoms, cytopenia, hepatosplenomegaly, fluid accumulation, cytokine storm-associated multiple organ system dysfunction, and is often fatal. In 1994, Kaposi sarcoma-associated herpesvirus/human herpesvirus-8 (HHV-8) was identified as the etiological driver of MCD in immunocompromised individuals. However, approximately 50% of MCD patients are HHV-8 negative (idiopathic MCD (iMCD)). Its idiopathic nature limits targeted treatment for iMCD patients who do not respond to anti-Interleukin-6 therapy. iMCD is itself heterogeneous, and recent work has identified at least one distinct sub-population of iMCD patients with a severe clinical presentation featuring thrombocytopenia, anasarca, myelofibrosis, renal dysfunction, and organomegaly (iMCD-TAFRO). Several hypotheses have been proposed to explain the pathophysiology of iMCD and UCD, all of which remain untested. One notable hypothesis entertains that iMCD and UCD are in fact driven by viral infection–either HHV-8 that is not detected by current diagnostic methods, a novel virus, or a known but unanticipated virus. In support of the last possibility, there are several case reports of associations with Epstein-Barr virus (EBV), HHV-6 and Hepatitis B virus (HBV); however, neither a systematic study of known viruses, nor a search for novel viruses in CD has been reported.To this end, we employed Virome Capture Sequencing for Vertebrate Viruses (VirCapSeq-VERT),-a RNA-hybrid capture, deep sequencing and bioinformatics pipeline designed for viral discovery. In accordance with the Treaty of Helsinki, we obtained freshly frozen lymph node tissue from patients with iMCD (n=11) and UCD (n=12) as experimental conditions. HHV-8-positive MCD (n=2) was included as a positive control for HHV-8 infection. Lymph nodes from patients with lymphoma without clinical suspicion of HHV-8 infection (n=6) and an additional reactive lymph node were included as a negative control. HHV-8 was only detected in HHV-8-positive MCD and not in iMCD or UCD, consistent with prior clinical testing. Additionally, we did not identify any previously unknown viruses in iMCD or UCD lymph node tissue. Members of the herpesviridae family, including EBV, HHV-6 and HHV-7, were found in all conditions. Interestingly, in iMCD, the identification of herpesviridae family members was associated with relapsing disease and the more clinically severe iMCD-TAFRO variant. Additional numerous associations of unclear significance were made with viruses such as Human Endogenous Retrovirus Type K (HERV-K), transfusion transmitted virus/Torque teno virus (TTV), and Pegivirus.To investigate the significance of the EBV infection, we analyzed the number of EBV positive cells by in situ hybridization on lymph node tissue from a separate cohort of patients with CD and related disorders. The mean number of Epstein-Barr virus-encoded small RNAs (EBER) positive cells/high-powered fields (HPF) across 10 HPF was significantly lower in UCD (2 ± 2.3; n=9) and iMCD (1.7 ± 2.8; n=12) than in HHV-8 positive MCD (106.5 ± 75.6; n=2) and EBV-associated lymphoproliferation (63.5 ± 54.4; n=2) (p < 0.005 for all comparisons). The only iMCD-TAFRO case in this cohort had 4 EBER-positive cells/HPF. Further study is needed with larger cohorts of patients to validate the prognostic and potentially pathogenic significance of these associations, and in particular, the association of EBV and other herpesviridae family members with iMCD-TAFRO. DisclosuresFajgenbaum:Janssen Pharmaceuticals: Research Funding.

Structural Mimicry Drives HIV-1 Rev-Mediated HERV-K Expression

Expression of the Human Endogenous Retrovirus Type K (HERV-K), the youngest and most active HERV, has been associated with various cancers and neurodegenerative diseases. As in all retroviruses, a fraction of HERV-K transcripts is exported from the nucleus in unspliced or incompletely spliced forms to serve as templates for translation of viral proteins. In a fraction of HERV-K loci (Type 2 proviruses), nuclear export of the unspliced HERV-K mRNA appears to be mediated by a cis-acting signal on the mRNA, the RcRE, and the protein Rec—these are analogous to the RRE-Rev system in HIV-1. Interestingly, the HIV-1 Rev protein is able to mediate the nuclear export of the HERV-K RcRE, contributing to elevated HERV-K expression in HIV-infected patients. We aimed to understand the structural basis for HIV Rev-HERV-K RcRE recognition. We examined the conformation of the RcRE RNA in solution using small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). We found that the 433-nt long RcRE can assume folded or extended conformations as observed by AFM. SAXS analysis of a truncated RcRE variant revealed an “A”-shaped topological structure similar to the one previously reported for the HIV-1 RRE. The effect of the overall topology was examined using several deletion variants. SAXS and biochemical analyses demonstrated that the “A” shape is necessary for efficient Rev-RcRE complex formation in vitro and nuclear export activity in cell culture. The findings provide insight into the mechanism of HERV-K expression and a structural explanation for HIV-1 Rev-mediated expression of HERV-K in HIV-infected patients. ImportanceExpression of the human endogenous retrovirus type K (HERV-K) has been associated with various cancers and autoimmune diseases. Nuclear export of both HIV-1 and HERV-K mRNAs is dependent on the interaction between a small viral protein (Rev in HIV-1 and Rec in HERV-K) and a region on the mRNA (RRE in HIV-1 and RcRE in HERV-K). HIV-1 Rev is able to mediate the nuclear export of RcRE-containing HERV-K mRNAs, which contributes to elevated production of HERV-K proteins in HIV-infected patients. We report the solution conformation of the RcRE RNA—the first three-dimensional topological structure for a HERV molecule—and find that the RcRE resembles the HIV-1 nuclear export signal, RRE. The finding reveals the structural basis for the increased HERV-K expression observed in HIV-infected patients. Elevated HERV expression, mediated by HIV infection or other stressors, can have various HERV-related biological consequences. The findings provide structural insight for regulation of HERV-K expression.

Human Endogenous Retrovirus K in Cancer: A Potential Biomarker and Immunotherapeutic Target.

In diseases where epigenetic mechanisms are changed, such as cancer, many genes show altered gene expression and inhibited genes become activated. Human endogenous retrovirus type K (HERV-K) expression is usually inhibited in normal cells from healthy adults. In tumor cells, however, HERV-K mRNA expression has been frequently documented to increase. Importantly, HERV-K-derived proteins can act as tumor-specific antigens, a class of neoantigens, and induce immune responses in different types of cancer. In this review, we describe the function of the HERV-K HML-2 subtype in carcinogenesis as biomarkers, and their potential as targets for cancer immunotherapy.

Retrovirus insertion site analysis of LGL leukemia patient genomes

BackgroundLarge granular lymphocyte (LGL) leukemia is an uncommon cancer characterized by sustained clonal proliferation of LGL cells. Antibodies reactive to retroviruses have been documented in the serum of patients with LGL leukemia. Culture or molecular approaches have to date not been successful in identifying a retrovirus.MethodsBecause a retrovirus must integrate into the genome of an infected cell, we focused our efforts on detecting a novel retrovirus integration site in the clonally expanded LGL cells. We present a new computational tool that uses long-insert mate pair sequence data to search the genome of LGL leukemia cells for retrovirus integration sites. We also utilize recently published methods to interrogate the status of polymorphic human endogenous retrovirus type K (HERV-K) provirus in patient genomes.ResultsOur data show that there are no new retrovirus insertions in LGL genomes of LGL leukemia patients. However, our insertion call tool did detect four HERV-K provirus integration sites that are polymorphic in the human population but absent from the human reference genome, hg19. To determine if the prevalence of these or other polymorphic proviral HERV-Ks differed between LGL leukemia patients and the general population, we used a recently developed tool that reports sites in the human genome occupied by a known proviral HERV-K. We report that there are significant differences in the number of polymorphic HERV-Ks in the genomes of LGL leukemia patients of European origin compared to individuals with European ancestry in the 1000 genomes (KGP) data.ConclusionsOur study confirms that the clonal expansion of LGL cells in LGL leukemia is not driven by the integration of a new infectious or endogenous retrovirus, although we do not rule out that these cells are responding to retroviral antigens produced in other cell types. However, our computational analyses revealed that the genomes of LGL leukemia patients carry a higher burden of polymorphic HERV-K proviruses compare to individuals from KGP of European ancestry. Our research emphasizes the merits of comprehensive genomic assessment of HERV-K in cancer samples and suggests that further analyses to determine contributions of HERV-K to LGL leukemia are warranted.

Correction: Downregulation of Human Endogenous Retrovirus Type K (HERV-K) Viral env RNA in Pancreatic Cancer Cells Decreases Cell Proliferation and Tumor Growth.

Correction: Downregulation of Human Endogenous Retrovirus Type K (HERV-K) Viral env RNA in Pancreatic Cancer Cells Decreases Cell Proliferation and Tumor Growth.

A computational framework to assess genome-wide distribution of polymorphic human endogenous retrovirus-K In human populations.

Human Endogenous Retrovirus type K (HERV-K) is the only HERV known to be insertionally polymorphic; not all individuals have a retrovirus at a specific genomic location. It is possible that HERV-Ks contribute to human disease because people differ in both number and genomic location of these retroviruses. Indeed viral transcripts, proteins, and antibody against HERV-K are detected in cancers, auto-immune, and neurodegenerative diseases. However, attempts to link a polymorphic HERV-K with any disease have been frustrated in part because population prevalence of HERV-K provirus at each polymorphic site is lacking and it is challenging to identify closely related elements such as HERV-K from short read sequence data. We present an integrated and computationally robust approach that uses whole genome short read data to determine the occupation status at all sites reported to contain a HERV-K provirus. Our method estimates the proportion of fixed length genomic sequence (k-mers) from whole genome sequence data matching a reference set of k-mers unique to each HERV-K locus and applies mixture model-based clustering of these values to account for low depth sequence data. Our analysis of 1000 Genomes Project Data (KGP) reveals numerous differences among the five KGP super-populations in the prevalence of individual and co-occurring HERV-K proviruses; we provide a visualization tool to easily depict the proportion of the KGP populations with any combination of polymorphic HERV-K provirus. Further, because HERV-K is insertionally polymorphic, the genome burden of known polymorphic HERV-K is variable in humans; this burden is lowest in East Asian (EAS) individuals. Our study identifies population-specific sequence variation for HERV-K proviruses at several loci. We expect these resources will advance research on HERV-K contributions to human diseases.

Abstract 1257: Human endogenous retrovirus type K (HERV-K) env protein as a vaccine target for HERV-K+ cancer prevention

Abstract Some tumors, including BC tumors, are poorly responsive or develop resistance to therapy, which creates an impetus to identify novel strategies that potentiate immunotherapy in unresponsive cancers. Vaccines against human BC have shown only limited success for prevention of BC, with the exception of yellow fever vaccine 17D (YFV), which is closely homologous to HERV-K. In order to check immune response in animal models, murine mammary tumor cells (4T1) or melanoma cells (B16F10) were employed to express a full-length HERV-K Env protein obtained from a BC patient with invasive ductal carcinoma (IDC) by stably transfecting with pLVXKenv [full-length HERV-K env, expressing extracellular surface (SU) and transmembrane (TM) domains] or pLVX vector (control). To determine whether the SU or TM has cancer-preventive effects when dosed as an HERV-K antigen vaccine, C57BL/6 female mice were immunized with cyclic dinucleotides (CDN:15 µg) and HERV-K SU (KSU), TM [harboring the HERV-K immunosuppressive domain (ISD)], or GST protein (25 µg) on day 1 and boosted on days 14 and 28. Mice were challenged with B16F10pLVX or B16F10pLVXKenv (3 X 105 cells) 18 days after the last boost of immunization. The effect of tumor challenge on tumor growth and weight was compared. Increased weight of pLVXKenv relative to pLVX control cells was observed in mice immunized with GST (2-fold increased weight). In contrast, we observed reduced weight of pLVXKenv relative to pLVX tumors in mice immunized with KSU (50% reduced weight), showing the protective effect of KSU vaccination. This protective effect disappeared in mice immunized with the TM (1.65-fold increased tumor weight), indicating that the ISD of TM may prevent an immune response to the vaccine. Increased anti-HERV-K antibody titers were demonstrated in mice immunized with KSU than with KTM. Significantly increased anti-KSU antibody titers were demonstrated in mice immunized with KSU than with GST. Interestingly, significantly increased anti-KTM antibody titers were demonstrated in mice inoculated with pLVXKenv than with pLVX. Lower percentages of CD3+CD4+, CD3+CD8+, and CD3-NK T cells from tumor tissues were observed in mice immunized with TM or SU protein and challenged with B16F10Kenv cells. Significantly increased proliferation of CD4 or CD8 T cells was demonstrated in mice immunized with KSU protein and challenged with B16F10Kenv cells than after challenge with B16F10pLVX cells. In contrast, significantly decreased proliferation of CD4 and CD8 T cells was demonstrated in mice immunized with TM and challenged with B16F10Kenv cells than with B16F10pLVX cells, reflecting immunosuppression induced by the TM vaccine. In conclusion, HERV-K SU protein, but not TM protein, can be used for cancer prevention and immunotherapy for HERV-K positive cancers. Also, TM blockade may reduce immunosuppression. Citation Format: Feng Wang-Johanning, Jia Li, Ming Li, Gary L. Johanning, Albert Lee, Tianhe Huang. Human endogenous retrovirus type K (HERV-K) env protein as a vaccine target for HERV-K+ cancer prevention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1257.

Downregulation of Human Endogenous Retrovirus Type K (HERV-K) Viral env RNA in Pancreatic Cancer Cells Decreases Cell Proliferation and Tumor Growth.

Purpose: We investigated the role of the human endogenous retrovirus type K (HERV-K) envelope (env) gene in pancreatic cancer.Experimental Design: shRNA was employed to knockdown (KD) the expression of HERV-K in pancreatic cancer cells.Results: HERV-K env expression was detected in seven pancreatic cancer cell lines and in 80% of pancreatic cancer patient biopsies, but not in two normal pancreatic cell lines or uninvolved normal tissues. A new HERV-K splice variant was discovered in several pancreatic cancer cell lines. Reverse transcriptase activity and virus-like particles were observed in culture media supernatant obtained from Panc-1 and Panc-2 cells. HERV-K viral RNA levels and anti-HERV-K antibody titers were significantly higher in pancreatic cancer patient sera (N = 106) than in normal donor sera (N = 40). Importantly, the in vitro and in vivo growth rates of three pancreatic cancer cell lines were significantly reduced after HERV-K KD by shRNA targeting HERV-K env, and there was reduced metastasis to lung after treatment. RNA-Seq results revealed changes in gene expression after HERV-K env KD, including RAS and TP53. Furthermore, downregulation of HERV-K Env protein expression by shRNA also resulted in decreased expression of RAS, p-ERK, p-RSK, and p-AKT in several pancreatic cancer cells or tumors.Conclusions: These results demonstrate that HERV-K influences signal transduction via the RAS-ERK-RSK pathway in pancreatic cancer. Our data highlight the potentially important role of HERV-K in tumorigenesis and progression of pancreatic cancer, and indicate that HERV-K viral proteins may be attractive biomarkers and/or tumor-associated antigens, as well as potentially useful targets for detection, diagnosis, and immunotherapy of pancreatic cancer. Clin Cancer Res; 23(19); 5892-911. ©2017 AACR.

Abstract LB-221: Tumor microenvironment predicts aggressive breast cancer: Combination of HERV-K, immune checkpoint and activation status of CD8+ T cells

Abstract The purpose of this study is to identify useful predictive biomarkers of anti-tumor cytotoxic T cell and immune checkpoint response, to optimize targeted therapy, chemotherapy, and immunotherapy of breast cancer (BC). Immune checkpoint markers (14 circulating proteins) in BC patients were determined using a magnetic bead assay. CD27, PDL-2, LAG-3, and TIM-3 levels in the plasma, obtained from patients with invasive ductal carcinoma (IDC: n=32), ductal carcinoma in situ (DCIS: n=11), other invasive BC (n=12), prophylactic surgery (BRCA1: n=7, and BRCA2 mutations: n=4, benign phyllodes tumor: n=2) were significantly enhanced compared with healthy controls (n=12), which supports a highly immune suppressed environment. Also, these markers were compared at T1 (before surgery), T2 (6 months post-surgery), and T3 (18 months post-surgery). LAG-3, CD27 (p=0.012), 4-1BB, CD80, PD-L2, PD-L1 (p=0.045), and IDO all had a decreased plasma concentrations post-surgery (6 months or 18 months) compared with pre-surgery. Interestingly, significantly higher concentrations of BTLA, IDO, LAG-3, PD-L2, TIM-3, and PD-L1 were detected in BC patients that had higher titers of circulating human endogenous retrovirus type K (HERV-K) antibodies. We characterized the subset distribution and phenotype of the immune cells of various BC patients. CD4+ or CD8+ T cells collected from breast tissues including tumor tissues (T) or uninvolved normal breast tissues (N) were analyzed for CD4 and CD8. Higher percentages of CD8+ tumor infiltrating lymphocyte (TIL) cells were detected in N compared with autologous T. The percentage of CD38+/HLA-DR+ CD8+ T cells was low in the PBMCs compared to percentages in TILs. Activated T cells were only detected in TIL (40% to 99%; n=6) but not in their PBMCs from the same patients. Several studies have demonstrated that regulatory T cells (Tregs) within the tumor environment lead to a decrease in patient survival. Higher percentages of Treg cells were observed in aggressive BC and in TIL obtained from tumor tissues compared to TIL cells obtained from uninvolved tissues. HERV-K specific CD8 T cells (K-T cells) enhanced the percentage of CD8 T cells (62.5%; n=8) in patients with aggressive BC, and were able to kill their autologous tumor cells or mammospheres. Significantly reduced tumor weights and metastases were demonstrated in MDA-MB-231 mice treated with K-T cells. The lower percentage of CD8 T cells and higher percentage of Treg T cells we observed in breast tumor tissues, coupled with elevated concentrations of circulating immune checkpoint proteins in BC patients, suggests a highly immune suppressed environment in these aggressive tumors that could be minimized with anti-HERV-K therapy. Thus, HERV-K T cell therapies combined with blockade of immune checkpoints may be a new regimen for treating aggressive BC. Citation Format: Feng Wang-Johanning, Jia Li, Gary Johanning, Ming Li, Raghu Chivukula, Guoqing Wu. Tumor microenvironment predicts aggressive breast cancer: Combination of HERV-K, immune checkpoint and activation status of CD8+ T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-221. doi:10.1158/1538-7445.AM2017-LB-221

HERV-K activation is strictly required to sustain CD133+ melanoma cells with stemness features

BackgroundMelanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance. CD133 positive (CD133+) subpopulation has also been suggested as putative cancer stem cell (CSC) of melanoma tumor. Human endogenous retrovirus type K (HERV-K) has been described to be aberrantly activated during melanoma progression and implicated in the etiopathogenesis of disease. Earlier, we reported that stress-induced HERV-K activation promotes cell malignant transformation and reduces the immunogenicity of melanoma cells. Herein, we investigated the correlation between HERV-K and the CD133+ melanoma cells during microenvironmental modifications.MethodsTVM-A12 cell line, isolated in our laboratory from a primary human melanoma lesion, and other commercial melanoma cell lines (G-361, WM-115, WM-266-4 and A375) were grown and maintained in the standard and stem cell media. RNA interference, Real-time PCR, flow cytometry analysis, self-renewal and migration/invasion assays were performed to characterize cell behavior and HERV-K expression.ResultsMelanoma cells, exposed to stem cell media, undergo phenotype-switching and expansion of CD133+ melanoma cells, concomitantly promoted by HERV-K activation. Notably, the sorted CD133+ subpopulation showed stemness features, characterized by higher self-renewal ability, embryonic genes expression, migration and invasion capacities compared to the parental cell line. RNA interference-mediated downregulation experiments showed that HERV-K has a decisive role to expand and maintain the CD133+ melanoma subpopulation during microenvironmental modifications. Similarly, non nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine were effective to restrain the activation of HERV-K in melanoma cells, to antagonize CD133+ subpopulation expansion and to induce selective high level apoptosis in CD133+ cells.ConclusionsHERV-K activation promotes melanoma cells phenotype-switching and is strictly required to expand and maintain the CD133+ melanoma cells with stemness features in response to microenvironmental modifications.

PP03. HUMAN ENDOGENOUS RETROVIRUS TYPE K (HERVK) PROTEINS ARE OVEREXPRESSED AND RELEASED FROM HUMAN PRIMARY SCHWANNOMA CELLS CONTRIBUTING TO TUMOUR DEVELOPMENT VIA ERK, AKT, FAK PATHWAYS ACTIVATION AND P53 DOWNREGULATION

Loss of function mutations in the gene coding for the tumour suppressor Merlin causes development of multiple tumours of the nervous system such as schwannomas, meningiomas and ependymomas. These tumours may occur spontaneously or as a part of the hereditary disease Neurofibromatosis type 2 (NF2). Current therapies, surgery and radiosurgery, are not fully effective and new drug treatments are urgently needed. Schwannoma is the most common Merlin-deficient tumour, a hallmark for NF2 and a model for all other Merlin-deficient tumours. Therefore, to study Merlin-deficient tumours and to test different drugs we have developed a schwannoma in vitro cell model. Using this model we have previously identified several targets and tested various drugs including Sorafenib, which we have in phase 0 clinical trials on NF2 patients. Our preliminary data suggest that a promising target for Merlin-deficient tumours is one group of endogenous retroviruses called HERVK (Human Endogenous Retrovirus type K). Endogenous retroviruses are viruses that have integrated themselves into germ-line chromosomes and thereby become part of human genome (8%). HERVK are overexpressed in several cancers and activate pathways known to be involved in schwannoma development such as NFkB, β-catenin, ERK and AKT. HERVK proteins are currently being investigated as potential immunotherapy targets for cancer and HIV. We find that HERVK envelope, capsid/gag, Rec and Np9 proteins are overexpressed in human primary schwannoma cells and tissues. Additionally, HERVK envelope and capsid proteins are released from schwannoma cells. HERVK envelope expression is Merlin dependent and both HERVK envelope and capcid/gag expression are transcriptionally and translationally regulated. Anti-HERVK antibodies reduced schwannoma proliferation, pERK/pAKT/ pFAK and cyclin D1 levels and increased expression of p53. Also, pre-incubation of schwannoma cells with anti-HERVK antibodies prior to treatment with Selumetinib potentiated drug’s efficiency. An HIV protease inhibitor with some potency for HERVK protease, Ritonavir, also decreased proliferation of schwannoma cells and increased the efficiency of Selumetinib, Sorafenib and BEZ235 when combined. We suggest that HERVK plays a relevant role in schwannoma and other Merlin-deficient tumours development.

Activation of HERV-K Env protein is essential for tumorigenesis and metastasis of breast cancer cells.

Human endogenous retrovirus type K (HERV-K) Env protein was previously demonstrated to be overexpressed in human breast cancer (BC) cells and tissues. However, the molecular pathways driving the specific alterations are unknown. We now show that knockdown of its expression with an shRNA (shRNAenv) blocked BC cell proliferation, migration, and invasion. shRNAenv transduction also attenuated the ability of BC cells to form tumors, and notably prevented metastasis. Mechanistically, downregulation of HERV-K blocked expression of tumor-associated genes that included Ras, p-RSK, and p-ERK. The major upstream regulators influenced by HERV-K knockdown were p53, TGF- β1, and MYC. Of interest, when the HERV-K env gene was overexpressed in shRNAenv-transduced BC cells using an HERV-K env expression vector, Ras/Raf/MEK/ERK pathway signaling was restored. CDK5, which alters p53 phosphorylation in some cancers, was upregulated and p53 was downregulated when HERV-K was overexpressed. CDK5 is also a mediator of TGF-β1-induced epithelial-mesenchymal transition and migration in cancer cells, and is involved in tumor formation. Importantly, reductions in migration, invasion, and transformation of BC cells stably transduced with shRNAenv was reversed after adding back a vector with a synonymous mutation of HERV-K env. Taken together, these results indicate that HERV-K Env protein plays an important role in tumorigenesis and metastasis of BC.

Expansion of a novel endogenous retrovirus throughout the pericentromeres of modern humans.

BackgroundApproximately 8% of the human genome consists of sequences of retroviral origin, a result of ancestral infections of the germ line over millions of years of evolution. The most recent of these infections is attributed to members of the human endogenous retrovirus type-K (HERV-K) (HML-2) family. We recently reported that a previously undetected, large group of HERV-K (HML-2) proviruses, which are descendants of the ancestral K111 infection, are spread throughout human centromeres.ResultsStudying the genomes of certain cell lines and the DNA of healthy individuals that seemingly lack K111, we discover new HERV-K (HML-2) members hidden in pericentromeres of several human chromosomes. All are related through a common ancestor, termed K222, which is a virus that infected the germ line approximately 25 million years ago. K222 exists as a single copy in the genomes of baboons and high order primates, but not New World monkeys, suggesting that progenitor K222 infected the primate germ line after the split between New and Old World monkeys. K222 exists in modern humans at multiple loci spread across the pericentromeres of nine chromosomes, indicating it was amplified during the evolution of modern humans.ConclusionsCopying of K222 may have occurred through recombination of the pericentromeres of different chromosomes during human evolution. Evidence of recombination between K111 and K222 suggests that these retroviral sequences have been templates for frequent cross-over events during the process of centromere recombination in humans.

Regulation of the human endogenous retrovirus K (HML-2) transcriptome by the HIV-1 Tat protein.

Approximately 8% of the human genome is made up of endogenous retroviral sequences. As the HIV-1 Tat protein activates the overall expression of the human endogenous retrovirus type K (HERV-K) (HML-2), we used next-generation sequencing to determine which of the 91 currently annotated HERV-K (HML-2) proviruses are regulated by Tat. Transcriptome sequencing of total RNA isolated from Tat- and vehicle-treated peripheral blood lymphocytes from a healthy donor showed that Tat significantly activates expression of 26 unique HERV-K (HML-2) proviruses, silences 12, and does not significantly alter the expression of the remaining proviruses. Quantitative reverse transcription-PCR validation of the sequencing data was performed on Tat-treated PBLs of seven donors using provirus-specific primers and corroborated the results with a substantial degree of quantitative similarity. The expression of HERV-K (HML-2) is tightly regulated but becomes markedly increased following infection with HIV-1, in part due to the HIV-1 Tat protein. The findings reported here demonstrate the complexity of the genome-wide regulation of HERV-K (HML-2) expression by Tat. This work also demonstrates that although HERV-K (HML-2) proviruses in the human genome are highly similar in terms of DNA sequence, modulation of the expression of specific proviruses in a given biological situation can be ascertained using next-generation sequencing and bioinformatics analysis.

Genomic flexibility of human endogenous retrovirus type K

Human endogenous retrovirus type K (HERV-K) proviruses are scattered throughout the human genome, but as no infectious HERV-K virus has been detected to date, the mechanism by which these viruses replicated and populated the genome remains unresolved. Here, we provide evidence that, in addition to the RNA genomes that canonical retroviruses package, modern HERV-K viruses can contain reverse-transcribed DNA (RT-DNA) genomes. Indeed, reverse transcription of genomic HERV-K RNA into the DNA form is able to occur in three distinct times and locations: (i) in the virus-producing cell prior to viral release, yielding a DNA-containing extracellular virus particle similar to the spumaviruses; (ii) within the extracellular virus particle itself, transitioning from an RNA-containing particle to a DNA-containing particle; and (iii) after entry of the RNA-containing virus into the target cell, similar to canonical retroviruses, such as murine leukemia virus and HIV. Moreover, using a resuscitated HERV-K virus construct, we show that both viruses with RNA genomes and viruses with DNA genomes are capable of infecting target cells. This high level of genomic flexibility historically could have permitted these viruses to replicate in various host cell environments, potentially assisting in their many integration events and resulting in their high prevalence in the human genome. Moreover, the ability of modern HERV-K viruses to proceed through reverse transcription and package RT-DNA genomes suggests a higher level of replication competency than was previously understood, and it may be relevant in HERV-K-associated human diseases. IMPORTANCE Retroviral elements comprise at least 8% of the human genome. Of all the endogenous retroviruses, HERV-K viruses are the most intact and biologically active. While a modern infectious HERV-K has yet to be found, HERV-K activation has been associated with cancers, autoimmune diseases, and HIV-1 infection. Thus, determining how this virus family became such a prevalent member of our genome and what it is capable of in its current form are of the utmost importance. Here, we provide evidence that HERV-K viruses currently found in the human genome are able to proceed through reverse transcription and historically utilized a life cycle with a surprising degree of genomic flexibility in which both RNA- and DNA-containing viruses were capable of mediating infection.

The viral oncogene Np9 acts as a critical molecular switch for co-activating β-catenin, ERK, Akt and Notch1 and promoting the growth of human leukemia stem/progenitor cells

HERV-K (human endogenous retrovirus type K) type 1-encoded Np9 is a tumor-specific biomarker, but its oncogenic role and targets in human leukemia remain elusive. We first identified Np9 as a potent viral oncogene in human leukemia. Silencing of Np9 inhibited the growth of myeloid and lymphoblastic leukemic cells, whereas expression of Np9 significantly promoted the growth of leukemia cells in vitro and in vivo. Np9 not only activated ERK, AKT and Notch1 pathways but also upregulated β-catenin essential for survival of leukemia stem cells. In human leukemia, Np9 protein level in leukemia patients was substantially higher than that in normal donors (56% vs 4.5%). Moreover, Np9 protein level was correlated with the number of leukemia stem/progenitor cells but not detected in normal CD34(+) hematopoietic stem cells. In addition, Np9-positive samples highly expressed leukemia-specific pol-env polyprotein, env and transmembrane proteins as well as viral particles. Thus, the viral oncogene Np9 is a critical molecular switch of multiple signaling pathways regulating the growth of leukemia stem/progenitor cells. These findings open a new perspective to understand the etiology of human common leukemia and provide a novel target for treating leukemia.

Evaluation of Cynomolgus Macaque (Macaca fascicularis) Endogenous Retrovirus Expression Following Simian Immunodeficiency Virus Infection

Human endogenous retrovirus type K (HERV-K) transcripts are upregulated in the plasma of HIV-infected individuals and have been considered as targets for an HIV vaccine. We evaluated cynomolgus macaque endogenous retrovirus (CyERV) mRNA expression by RT-qPCR in PBMCs isolated from a cohort of animals previously utilized in a live attenuated SIV vaccine trial. CyERV env transcript levels decreased following vaccination (control and vaccine groups) and CyERV env and gag mRNA expression was decreased following acute SIV-infection, whereas during chronic SIV infection, CyERV transcript levels were indistinguishable from baseline. Reduced susceptibility to initial SIV infection, as measured by the number of SIV challenges required for infection, was associated with increased CyERV transcript levels in PBMCs. In vitro analysis revealed that SIV infection of purified CD4+ T-cells did not alter CyERV gene expression. This study represents the first evaluation of ERV expression in cynomolgus macaques following SIV infection, in an effort to assess the utility of cynomolgus macaques as an animal model to evaluate ERVs as a target for an HIV/SIV vaccine. This non-human primate model system does not recapitulate what has been observed to date in the plasma of HIV-infected humans suggesting that further investigation at the cellular level is required to elucidate the impact of HIV/SIV infection on endogenous retrovirus expression.