Heterogeneous expression of the atypical chemokine receptor ACKR3 in glioblastoma patient-derived tissue samples and cell cultures.

Background: Glioblastoma (GBM) is the most aggressive glial tumor of the adult brain, associated with invariably fatal outcome, and a deeper understanding of the underlying malignant mechanisms is necessary to address the current therapeutic failure. We previously demonstrated the role of the CXCL12/CXCR4 axis in GBM cell migration and resistance to ionizing radiation. The atypical receptor ACKR3, responsible for CXCL12 scavenging, was previously suggested as additional important player in the context of GBM. Methods: Flow cytometry was used on GBM cell lines and patient-derived GBM cell cultures to quantify the level of ACKR3 expression. Moreover, we have at our disposal patient- derived formalin-fixed paraffin-embedded (FFPE) tissue, which is used for immunofluorescent analysis to characterize precisely ACKR3-positive cells. We used also an orthotopic xenograft model to study the impact of ACKR3 in vivo . Finally, qPCR analysis was also realized to study different gene expression on GBM cells. Results: Following validation of our detection tools, we observed that ACKR3 is expressed within GBM patient tumor tissue, distributed in diverse cell types. In contrast to CXCR4, ACKR3 expression in patient-derived stem-like cells (GSCs) remains very low while ACKR3 gene expression by tumor cells appears to be modulated by the in vivo environment. Using overexpression models, we also showed that in vitro ACKR3 had no significant effect on cell proliferation or invasion. Conclusions: Altogether, these results suggest that ACKR3 plays a minor role in malignant GBM cells, although its expression is possibly regulated by in vivo influences. The subtle and multifaceted functions ACKR3 could exert in GBM should therefore only be tackled within a comprehensive tumor microenvironment considering tumoral but also non-tumoral cells.