GPR56/ADGRG1 inhibits mesenchymal differentiation and radioresistance in glioblastoma

A mesenchymal transition occurs both during the natural evolution of glioblastoma (GBM) and in response to therapy. Here, we report that the adhesion G-protein-coupled receptor, GPR56/ADGRG1, inhibits GBM mesenchymal differentiation and radioresistance. GPR56 is enriched in proneural and classical GBMs and is lost during their transition toward a mesenchymal subtype. GPR56 loss of function promotes mesenchymal differentiation and radioresistance of glioma initiating cells both in vitro and in vivo. Accordingly, a low GPR56-associated signature is prognostic of a poor outcome in GBM patients even within non-G-CIMP GBMs. Mechanistically, we reveal GPR56 as an inhibitor of the nuclear factor kappa B (NF-κB) signaling pathway, thereby providing the rationale by which this receptor prevents mesenchymal differentiation and radioresistance. A pan-cancer analysis suggests that GPR56 might be an inhibitor of the mesenchymal transition across multiple tumor types beyond GBM

Neural Stem Cell Factors as Important Players in Glioblastoma Pathogenesis

[eng] The main goal of this PhD thesis was to understand the mechanisms underlying GBM tumor formation and progression, with a special emphasis on the study of factors that have a role in normal NSC biology, which might be providing cancer cells with the stem-like properties required to acquire tumorigenic potential. With this purpose, this PhD thesis was divided into two different projects. 1. Transcriptional profiling of hypoxic NSC identifies calcineurin-NFATc4 signaling as a major regulator of NSC biology. One of the main goals of our laboratory is to get a deeper understanding of NSC biology as a first step prior to applying this knowledge to the study of gliomas. Therefore, in the first project of this PhD thesis, we set out to identify novel factors that control NSC biology (whose role in NSC was previously unknown). The specific objectives of this project have been: - Characterization of the effect of physiologic oxygen concentrations on NSC biology. - Identification of novel signaling pathways that are operative in NSC cultured under physiologic oxygen concentrations. - Identification of novel TF that orchestrate the NSC response to physiological oxygen concentrations - Functional validation of the role of NFATc4, one of the most promising candidate TF identified above on NSC properties under physiologic oxygen concentrations. 2. GPR56 is a NSC factor that restricts the proneural to mesenchymal transition in GBM by inhibiting the NF-kB pathway. The second project was focused on the identification of factors that are involved in GBM progression from a PN to a MES subtype (PN-to-MES transition). In a candidate-driven approach, we selected GPR56 as the focus of our studies based on its high enrichment in normal NSC as well as its function as an adhesion receptor. The main objectives of this project are listed below: - Characterization of GPR56 expression in the adult mouse brain and during ESC differentiation into the neural lineage. - Evaluation of GPR56 expression in the different GBM subtypes and correlation with GBM subtype markers. - Functional characterization of the impact of GPR56 knockdown in GIC in vitro and in vivo. - Characterization of the role of GPR56 as an adhesion molecule in GBM. - Study of the transcriptional regulation and signaling mediators of the GPR56 pathway. - Clinical association studies between GPR56 and the GPR56-associated signature and GBM clinical features, including patient survival and MRI characteristics. - Evaluation of the expression of GPR56 and GPR56-associated signature in other tumor types beyond GBM

PAF promotes stemness and radioresistance of glioma stem cells.

An integrated genomic and functional analysis to elucidate DNA damage signaling factors promoting self-renewal of glioma stem cells (GSCs) identified proliferating cell nuclear antigen (PCNA)-associated factor (PAF) up-regulation in glioblastoma. PAF is preferentially overexpressed in GSCs. Its depletion impairs maintenance of self-renewal without promoting differentiation and reduces tumor-initiating cell frequency. Combined transcriptomic and metabolomic analyses revealed that PAF supports GSC maintenance, in part, by influencing DNA replication and pyrimidine metabolism pathways. PAF interacts with PCNA and regulates PCNA-associated DNA translesion synthesis (TLS); consequently, PAF depletion in combination with radiation generated fewer tumorspheres compared with radiation alone. Correspondingly, pharmacological impairment of DNA replication and TLS phenocopied the effect of PAF depletion in compromising GSC self-renewal and radioresistance, providing preclinical proof of principle that combined TLS inhibition and radiation therapy may be a viable therapeutic option in the treatment of glioblastoma multiforme (GBM). Proc Natl Acad Sci U S A 2017 Oct 24; 114(43):E9086-E9095

Epigenetic Activation of WNT5A Drives Glioblastoma Stem Cell Differentiation and Invasive Growth

Glioblastoma stem cells (GSCs) are implicated in tumor neovascularization, invasiveness, and therapeutic resistance. To illuminate mechanisms governing these hallmark features, we developed a de novo glioblastoma multiforme (GBM) model derived from immortalized human neural stem/progenitor cells (hNSCs) to enable precise system-level comparisons of pre-malignant and oncogene-induced malignant states of NSCs. Integrated transcriptomic and epigenomic analyses uncovered a PAX6/DLX5 transcriptional program driving WNT5A-mediated GSC differentiation into endothelial-like cells (GdECs). GdECs recruit existing endothelial cells to promote peritumoral satellite lesions, which serve as a niche supporting the growth of invasive glioma cells away from the primary tumor. Clinical data reveal higher WNT5A and GdECs expression in peritumoral and recurrent GBMs relative to matched intratumoral and primary GBMs, respectively, supporting WNT5A-mediated GSC differentiation and invasive growth in disease recurrence. Thus, the PAX6/DLX5-WNT5A axis governs the diffuse spread of glioma cells throughout the brain parenchyma, contributing to the lethality of GBM

Epigenetic Activation of WNT5A Drives Glioblastoma Stem Cell Differentiation and Invasive Growth

Glioblastoma stem cells (GSCs) are implicated in tumor neovascularization, invasiveness, and therapeutic resistance. To illuminate mechanisms governing these hallmark features, we developed a de novo glioblastoma multiforme (GBM) model derived from immortalized human neural stem/progenitor cells (hNSCs) to enable precise system-level comparisons of pre-malignant and oncogene-induced malignant states of NSCs. Integrated transcriptomic and epigenomic analyses uncovered a PAX6/DLX5 transcriptional program driving WNT5A-mediated GSC differentiation into endothelial-like cells (GdECs). GdECs recruit existing endothelial cells to promote peritumoral satellite lesions, which serve as a niche supporting the growth of invasive glioma cells away from the primary tumor. Clinical data reveal higher WNT5A and GdECs expression in peritumoral and recurrent GBMs relative to matched intratumoral and primary GBMs, respectively, supporting WNT5A-mediated GSC differentiation and invasive growth in disease recurrence. Thus, the PAX6/DLX5-WNT5A axis governs the diffuse spread of glioma cells throughout the brain parenchyma, contributing to the lethality of GBM