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 1

HML-2 envelope protein is elevated in glioblastoma.

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HML-2 envelope protein is elevated in glioblastoma. (A–G) Envelope prote...
(A–G) Envelope protein is heterogeneously expressed in glioblastoma tissue using immunofluorescence and is expressed in most patients with glioblastoma (n = 8; 89%) (H) HERV-K envelope protein is not expressed in epilepsy control tissue (temporal neocortex). (I) HERV-K envelope RNA and HPRT copy numbers from epilepsy tissue and glioma samples were measured by digital-droplet PCR. HERV-K RNA/HPRT ratio and absolute copy numbers were elevated in patients with glioma compared with patients with epilepsy in the control group (Mann-Whitney test, **P = 0.01; mean = 1.15 ± 0.2 vs. 0.5 ± 0.2). (J) HERV-K DNA and RPP30 copy numbers from perilesional CSF were measured by digital-droplet PCR. The absolute value of HERV-K DNA/RPP30 of patients with high-grade gliomas (mean = 35.2 ± 8.8; n = 9) was significantly greater than that of patients with epilepsy (unpaired t test, *P = 0.02; 23.1 ± 6.7, n = 9). (K) HERV-K envelope protein is expressed in patient-derived glioma neurospheres (middle) but not widely expressed in established A172 adherent glioma cell lines (left). HERV-K ENV RNA transcripts as measured by qPCR correlate to protein expression: patient-derived neurosphere cell line GBM43 had significantly higher HERV-K ENV RNA than A172 (ANOVA, *P < 0.05) (right). Original magnification, ×10 (A–G). Scale bars: 10 μm (A–G and K, insets, and K); 20 μm (H, inset); 50 μm (K, right); 100 μm (H and K, left).