Gymnastik- och idrottshögskolan, GIH

Background Malignant gliomas, the most common malignant brain tumors in adults, represent a heterogeneous group of diseases with poor prognosis. Retroviruses can cause permanent genetic alterations that modify genes close to the viral integration site. Methods Here we describe the use of a high-throughput pipeline coupled to the commonly used tissue-specific retroviral RCAS-TVA mouse tumor model system. Utilizing next-generation sequencing, we show that retroviral integration sites can be reproducibly detected in malignant stem cell lines generated from RCAS-PDGFB-driven glioma biopsies. Results A large fraction of common integration sites contained genes that have been dysregulated or misexpressed in glioma. Others overlapped with loci identified in previous glioma-related forward genetic screens, but several novel putative cancer-causing genes were also found. Integrating retroviral tagging and clinical data, Ppfibp1 was highlighted as a frequently tagged novel glioma-causing gene. Retroviral integrations into the locus resulted in Ppfibp1 upregulation, and Ppfibp1-tagged cells generated tumors with shorter latency on orthotopic transplantation. In human gliomas, increased PPFIBP1 expression was significantly linked to poor prognosis and PDGF treatment resistance. Conclusions Altogether, the current study has demonstrated a novel approach to tagging glioma genes via forward genetics, validating previous results, and identifying PPFIBP1 as a putative oncogene in gliomagenesis.

Glioblastoma (GBM) is the most common and lethal primary malignant brain tumor which lacks efficient treatment and predictive biomarkers. Expression of the epithelial stem cell marker Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) has been described in GBM, but its functional role has not been conclusively elucidated. Here, we have investigated the role of LGR5 in a large repository of patient-derived GBM stem cell (GSC) cultures. The consequences of LGR5 overexpression or depletion have been analyzed using in vitro and in vivo methods, which showed that, among those with highest LGR5 expression (LGR5(high)), there were two phenotypically distinct groups: one that was dependent on LGR5 for its malignant properties and another that was unaffected by changes in LGR5 expression. The LGR5-responding cultures could be identified by their significantly higher self-renewal capacity as measured by extreme limiting dilution assay (ELDA), and these LGR5(high)-ELDA(high) cultures were also significantly more malignant and invasive compared to the LGR5(high)-ELDA(low) cultures. This showed that LGR5 expression alone would not be a strict marker of LGR5 responsiveness. In a search for additional biomarkers, we identified LPAR4, CCND2, and OLIG2 that were significantly upregulated in LGR5-responsive GSC cultures, and we found that OLIG2 together with LGR5 were predictive of GSC radiation and drug response. Overall, we show that LGR5 regulates the malignant phenotype in a subset of patient-derived GSC cultures, which supports its potential as a predictive GBM biomarker. Copyright (c) 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

High-grade gliomas (HGGs) are the most aggressive and invasive primary brain tumors. The platelet-derived growth factor (PDGF) signaling pathway drives HGG progression, and enhanced expression of PDGF receptors (PDGFRs) is a well-established aberration in a subset of glioblastomas (GBMs). PDGFRA is expressed in glioma cells, whereas PDGFRB is mostly restricted to the glioma-associated stroma. Here we show that the spatial location of TAMMs correlates with the expansion of a subset of tumor cells that have acquired expression of PDGFRB in both mouse and human low-grade glioma and HCGs. Furthermore, M2-polarized microglia but not bone marrow (BM)-derived macrophages (BMDMs) induced PDGFRB expression in glioma cells and stimulated their migratory capacity. These findings illustrate a heterotypic cross-talk between microglia and glioma cells that may enhance the migratory and invasive capacity of the latter by inducing PDGFRB.

Background

MicroRNAs (miRNAs) and their role during tumor development have been studied in greatdetail during the last decade, albeit their expression pattern and regulation during normaldevelopment are however not so well established. Previous studies have shown that miRNAsare differentially expressed in solid human tumors. Platelet-derived growth factor (PDGF)signaling is known to be involved in normal development of the brain as well as in malignantprimary brain tumors, gliomas, but the complete mechanism is still lacking. We decided toinvestigate the expression of the oncogenic miR-21 during normal mouse development andglioma, focusing on PDGF signaling as a potential regulator of miR-21.

Methods

We generated mouse glioma using the RCAS/tv-a system for driving PDGF-BB expression ina cell-specific manner. Expression of miR-21 in mouse cell cultures and mouse brain wereassessed using Northern blot analysis and in situ hybridization. Immunohistochemistry andWestern blot analysis were used to investigate SOX2 expression. LNA-modified siRNA wasused for irreversible depletion of miR-21. For inhibition of PDGF signaling Gleevec(imatinib mesylate), Rapamycin and U0126, as well as siRNA were used. Statisticalsignificance was calculated using double-sided unpaired Student´s t-test.

Results

We identified miR-21 to be highly expressed during embryonic and newborn braindevelopment followed by a gradual decrease until undetectable at postnatal day 7 (P7), thiscorrelated with SOX2 expression. Furthermore, miR-21 and SOX2 showed up-regulation andoverlapping expression pattern in RCAS/tv-a generated mouse brain tumor specimens. Uponirreversible depletion of miR-21 the expression of SOX2 was strongly diminished in bothmouse primary glioma cultures and human glioma cell lines. Interestingly, in normalfibroblasts the expression of miR-21 was induced by PDGF-BB, and inhibition of PDGFsignaling in mouse glioma primary cultures resulted in suppression of miR-21 suggesting thatmiR-21 is indeed regulated by PDGF signaling.

Conclusions

Our data show that miR-21 and SOX2 are tightly regulated already during embryogenesisand define a distinct population with putative tumor cell of origin characteristics. We believethat miR-21 is a mediator of PDGF-driven brain tumors, which suggests miR-21 as apromising target for treatment of glioma.