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 3

HERV-K corresponds to a poor overall outcome.

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HERV-K corresponds to a poor overall outcome. (A) Mean HML-2 expression ...
(A) Mean HML-2 expression was significantly higher in high-grade glioma tissue (n = 71) relative to that of normal control brain tissue (t test, P < 0.0001; 2.17 ± 0.02 vs. 1.08 ± 0.06; n = 100). Mean LTR5A, LTR5B, and LTR5Hs expression was significantly higher in GBM tissue relative to that in normal control tissue (t test, **P = 0.0018, ****P < 0.0001). Mean full-length HML-2 polymerase expression was overexpressed compared with that in normal control brain tissue (t test, *P = 0.01). (B) Impact of transcript expression on OS in patients with GBM. Patients with GBM with higher expression of HML-2 with intact ORF demonstrated significantly worse OS relative to patients with lower mean HML-2 expression (Mantel-Cox test, P = 0.011). Patients with GBM with higher expression of HML-2 full-length gag (Mantel-Cox test, P = 0.027), pol (Mantel-Cox test, P = 0.0068) and env (Mantel-Cox test, P = 0.028) demonstrated worse OS relative to patients with lower respective HML-2 transcripts. No significant differences in OS between patients with high and low LTR5A, LTR5B, and LTR5Hs expression were found. Cutoff values for high and low expressing groups were determined using maximally ranked statistics as detailed in the R package survminer. The cutoffs (FPKM) used were as follows: mean ORF, 88.3; LTR5A, 30.73; LTR5B, 39.46; LTR5Hs, 39.02; gag2, 8.20; pol2, 15.54; env2,23.50. (C) Relationship between HML-2 coding loci and Verhaak glioma classification. There were no significant differences in LTR5A or LTR5B expression across Verhaak states. However, MTC tumors demonstrated significantly reduced expression of HML-2 loci with LTR5Hs relative to GPC, PPR, and NEU tumors (ANOVA, P = 0.01, 0.02, 0.002). With respect to mean full-length gag expression, GPC lineage tumors had higher expression relative to that of MTC and NEU lineage tumors (ANOVA, P = 0.001, 0.005). MTC lineage tumors demonstrated reduced mean full-length pol expression relative to that of GPC, NEU, and PPR lineage tumors (ANOVA, multiple testing corrections, P = 0.003, 0.008, 0.01). MTC lineage tumors also demonstrated reduced mean full-length env expression with respect to NEU and PPR lineage tumors (P = 0.02, 0.01). GPC, glycolytic/plurimetabolic cellular state; MTC, mitochondrial; NEU, neuronal; PRR, proliferative/progenitor. *P < 0.05, **P < 0.01.