Human endogenous retrovirus K contributes to a stem cell niche in glioblastoma
Ashish H. Shah, … , John D. Heiss, Avindra Nath
Ashish H. Shah, … , John D. Heiss, Avindra Nath
Published July 3, 2023
Citation Information: J Clin Invest. 2023;133(13):e167929. https://doi.org/10.1172/JCI167929.
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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 7

Downregulation of HERV-K using CRISPRi reduces the glioblastoma stem cell phenotype.

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Downregulation of HERV-K using CRISPRi reduces the glioblastoma stem cel...
(A) CRISPR/dCas9-HERV-K significantly reduced neurosphere formation compared with nonguiding CRISPR/dCas9 in 3 biological replicates (2-way ANOVA, P < 0.0001). Scale bars: 400 μm. (B) CRISPR/dCas9-HERV-K significantly reduced HERV-K env, Polymerase, and Nestin transcripts in GBM28 and GBM43. OCT4 transcripts were significantly reduced in GBM 43. (Unpaired t test, *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001). (C) RNA in situ hybridization demonstrated reduced HERV-K env, OCT4, and Nestin transcripts 48 hours after transfection with CRISPR/dCas9-HERV-K plasmids. Scale bars: 50 μm. (D) Protein immunofluorescence demonstrated reduced HERV-K envelope and OCT4 expression 72 hours after transfection with CRISPR/dCas9-HERV-K plasmids compared with ngCRISPR/dCas9 in patient-derived glioma neurospheres. Scale bars: 20 μm.