Human endogenous retrovirus K contributes to a stem cell niche in glioblastoma
Ashish H. Shah, Sarah R. Rivas, Tara T. Doucet-O’Hare, Vaidya Govindarajan, Catherine DeMarino, Tongguang Wang, Leonel Ampie, Yong Zhang, Yeshavanth Kumar Banasavadi-Siddegowda, Stuart Walbridge, Dragan Maric, Marta Garcia-Montojo, Robert K. Suter, Myoung-Hwa Lee, Kareem A. Zaghloul, Joseph Steiner, Abdel G. Elkahloun, Jay Chandar, Deepa Seetharam, Jelisah Desgraves, Wenxue Li, Kory Johnson, Michael E. Ivan, Ricardo J. Komotar, Mark R. Gilbert, John D. Heiss, Avindra Nath
Ashish H. Shah, Sarah R. Rivas, Tara T. Doucet-O’Hare, Vaidya Govindarajan, Catherine DeMarino, Tongguang Wang, Leonel Ampie, Yong Zhang, Yeshavanth Kumar Banasavadi-Siddegowda, Stuart Walbridge, Dragan Maric, Marta Garcia-Montojo, Robert K. Suter, Myoung-Hwa Lee, Kareem A. Zaghloul, Joseph Steiner, Abdel G. Elkahloun, Jay Chandar, Deepa Seetharam, Jelisah Desgraves, Wenxue Li, Kory Johnson, Michael E. Ivan, Ricardo J. Komotar, Mark R. Gilbert, John D. Heiss, Avindra Nath
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Research Article Virology

Human endogenous retrovirus K contributes to a stem cell niche in glioblastoma

Abstract

Human endogenous retroviruses (HERVs) are ancestral viral relics that constitute nearly 8% of the human genome. Although normally silenced, the most recently integrated provirus HERV-K (HML-2) can be reactivated in certain cancers. Here, we report pathological expression of HML-2 in malignant gliomas in both cerebrospinal fluid and tumor tissue that was associated with a cancer stem cell phenotype and poor outcomes. Using single-cell RNA-Seq, we identified glioblastoma cellular populations with elevated HML-2 transcripts in neural progenitor–like cells (NPC-like) that drive cellular plasticity. Using CRISPR interference, we demonstrate that HML-2 critically maintained glioblastoma stemness and tumorigenesis in both glioblastoma neurospheres and intracranial orthotopic murine models. Additionally, we demonstrate that HML-2 critically regulated embryonic stem cell programs in NPC-derived astroglia and altered their 3D cellular morphology by activating the nuclear transcription factor OCT4, which binds to an HML-2–specific long-terminal repeat (LTR5Hs). Moreover, we discovered that some glioblastoma cells formed immature retroviral virions, and inhibiting HML-2 expression with antiretroviral drugs reduced reverse transcriptase activity in the extracellular compartment, tumor viability, and pluripotency. Our results suggest that HML-2 fundamentally contributes to the glioblastoma stem cell niche. Because persistence of glioblastoma stem cells is considered responsible for treatment resistance and recurrence, HML-2 may serve as a unique therapeutic target.

Authors

Ashish H. Shah, Sarah R. Rivas, Tara T. Doucet-O’Hare, Vaidya Govindarajan, Catherine DeMarino, Tongguang Wang, Leonel Ampie, Yong Zhang, Yeshavanth Kumar Banasavadi-Siddegowda, Stuart Walbridge, Dragan Maric, Marta Garcia-Montojo, Robert K. Suter, Myoung-Hwa Lee, Kareem A. Zaghloul, Joseph Steiner, Abdel G. Elkahloun, Jay Chandar, Deepa Seetharam, Jelisah Desgraves, Wenxue Li, Kory Johnson, Michael E. Ivan, Ricardo J. Komotar, Mark R. Gilbert, John D. Heiss, Avindra Nath

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Figure 9

HERV-K induces astrocytic dedifferentiation and a tumorigenic phenotype.

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HERV-K induces astrocytic dedifferentiation and a tumorigenic phenotype....
(A) Transfection of glioblastoma neurospheres with pC-HK results in increased HML-2 envelope protein expression and increased OCT4 expression (original magnification, ×20). (B) HML2 leads to increased expression of HERV-K ENV (P < 0.03) and OCT4 (P < 0.03) transcripts in CD34+ astroglia. *P < 0.05. (C) HML2 also induced increased cellular migration and satellitosis in NSC-derived astrocytes. Scale bars: 400 μm. (D) Schematic demonstrating OCT4-mediated transcriptional activation of HERV-K within integrated NPC-like cellular state. Image created with BioRender. (E) Untransfected cells are responsible for intracranial tumor engraftment and retain prominent HERV-K envelope expression. Images were taken (original magnification, ×10 and ×20) at the tumor-parenchymal interface. Normal mouse brain does not express HERV-K envelope protein. Scale bars: 200 μm. (F) Engrafted tumors share similar morphology among ngCRISPR (day 18) and CRISPR/dCas9-HERV-K (day 33), with characteristic central necrosis on H&E staining and silver staining. Scale bars: 1 mm. (G) Transient inhibition of HERV-K improved survival in patient-derived orthotopic xenograft glioma models. Mice implanted with CRISPR/dCas9-HERV-K demonstrated longer overall survival than ngCRISPR/dCas9 controls (Grehan-Breslow-Wilcoxon test, P = 0.0008; OS, 26 days vs. 18.6).