Overexpression of Endogenous Retroviruses and Malignancy Markers in Neuroblastoma Cell Lines by Medium-Induced Microenvironmental Changes

Abstract

Neuroblastoma (NB) is the commonest solid tumor outside the central nervous system in infancy and childhood with a unique biological heterogeneity. In patients with advanced, metastasizing neuroblastoma, treatment failure and poor prognosis is often marked by resistance to chemo- or immunotherapy. Thus, identification of robust biomarkers seems essential for understanding tumor progression and developing effective therapy. Here, we have studied the expression of human endogenous retroviruses (HERV) as potential targets in NB cell lines during stem-cell medium-induced microenvironmental change. Quantitative PCR revealed that relative expression of the HERV-K family and HERV-W1 ENV were increased in all three NB cell lines after incubation in stem-cell medium. Virus transcriptome analyses revealed the transcriptional activation of three endogenous retrovirus elements: HERV-R ENV (ERV3-1), HERV-E1 and HERV-Fc2 ENV (ERVFC1-1). Known malignancy markers in NB, e.g. proto-oncogenic MYC or MYCN were expressed highly heterogeneously in the three investigated NB cell lines with up-regulation of MYC and MYCN upon medium-induced microenvironmental change. In addition, SiMa cells exclusively showed a phenotype switching from loosely-adherent monolayers to low proliferating grape-like cellular aggregates, which was accompanied by an enhanced CD133 expression. Interestingly, the overexpression of HERV was associated with a significant elevation of immune checkpoint molecule CD200 in both quantitative PCR and RNA-seq analysis suggesting tumor escape mechanism in NB cell lines after incubation in serum-free stem cell medium.

A Systematic Review of Expression and Immunogenicity of Human Endogenous Retroviral Proteins in Cancer and Discussion of Therapeutic Approaches

“…Serum from head and neck cancer patients exhibited an immune-suppressive function in macrophage polarization assays, and this ability could be blocked by antibodies specific for murine γ-retrovirus p15E immunosuppressive domain [123,124]. A much more recent study confirmed that HERV-H, also of the γ-retrovirus family, is differentially transcribed in head and neck cancers as the only HERV consistently identified [125], indicating that this may be the factor identified by Tan et al Likewise, HERV-K RNA has been detected in hepatocellular carcinoma [126] and HERV-K and W RNA in neuroblastoma cell lines [127,128]. Thus, there is still exciting ground to cover in the field of HERVs and cancer, and studies systematically evaluating HERV translation in cancer may pave the way for new therapeutic targets and modalities.…”

Molecular mechanisms of syncytin-1 in tumors and placental development related diseases

“…Chen et al and Li et al all found that the expression of syncytin-1 in NB cell lines SH-SY5Y and IMR-32 was significantly higher than that in normal cells [97,98]. Hu et al came to the same conclusion in NB cell lines SH-SY5Y, IMR-32, SK-N-DZ [99], Wieland et al in SH-SY5Y, IMR-32, SiMa [96], and Liu et al in SH-SY5Y [100]. Although syncytin-1 is overexpressed in NB cell lines, further studies in NB tumor tissues are needed in the future.…”

“…Radiation therapy is now the standard of care for high-risk NB, and this treatment is important for local lesion clearance and prevention of local recurrence [ 95 ], but the detection of other metastatic lesions in vivo and the degree of prognosis remain unclear. Treatment failure and poor prognosis are often marked by resistance to chemotherapy or immunotherapy in patients with advanced metastatic NB [ 96 ]. Therefore, the identification of reliable biomarkers is of great significance for understanding and treating NB.…”

“…Thirdly, changes in the medium micro-environment can also affect the expression of syncytin-1. The expression of syncytin-1 in the NB cell line SH-SY5Y was significantly increased in serum-free stem cell medium, and RNA analysis found that the overexpression of HERV was associated with the overexpression of the immune checkpoint molecule CD200 in NB tumors [ 96 ], indicating that serum-free stem cell medium promotes NB cell invasion [ 105 ]. Therefore, caffeine, aspirin, oxygen tension, DNA methylation and the medium micro-environment changes both can affect the expression of syncytin-1.…”

MYCN in Neuroblastoma: “Old Wine into New Wineskins”

“…The transcription factor gene associated with neuroblastoma is the oncogene MYCN that encodes a DNA-binding protein and is located on the 2p24 chromosome [ 37 ]. A recent study showed that in neuroblastoma the human endogenous retroviruses was abundant, indicating a possible role in the ontogenesis of the disease [ 38 ]. Interestingly, another recent report has shown that enterovirii responsible for other conditions, are implicated in the nerve tissue and possibly in tumorigenesis, including neuroblastoma [ 39 ].…”