Microglial Stimulation of Glioblastoma Invasion Involves Epidermal Growth Factor Receptor (EGFR) and Colony Stimulating Factor 1 Receptor (CSF-1R) Signaling
Glioblastoma multiforme is a deadly cancer for which current treatment options are limited. The ability of glioblastoma tumor cells to infiltrate the surrounding brain parenchyma critically limits the effectiveness of current treatments. We investigated how microglia, the resident macrophages of the brain, stimulate glioblastoma cell invasion. We first examined the ability of normal microglia from C57Bl/6J mice to stimulate GL261 glioblastoma cell invasion in vitro. We found that microglia stimulate the invasion of GL261 glioblastoma cells by approximately eightfold in an in vitro invasion assay. Pharmacological inhibition of epidermal growth factor receptor (EGFR) strongly inhibited microglia-stimulated invasion. Furthermore, blockade of colony stimulating factor 1 receptor (CSF-1R) signaling using ribonucleic acid (RNA) interference or pharmacological inhibitors completely inhibited microglial enhancement of glioblastoma invasion. GL261 cells were found to constitutively secrete CSF-1, the levels of which were unaffected by epidermal growth factor (EGF) stimulation, EGFR inhibition or coculture with microglia. CSF-1 only stimulated microglia invasion, whereas EGF only stimulated glioblastoma cell migration, demonstrating a synergistic interaction between these two cell types. Finally, using PLX3397 (a CSF-1R inhibitor that can cross the blood-brain barrier) in live animals, we discovered that blockade of CSF-1R signaling in vivo reduced the number of tumor-associated microglia and glioblastoma invasion. These data indicate that glioblastoma and microglia interactions mediated by EGF and CSF-1 can enhance glioblastoma invasion and demonstrate the possibility of inhibiting glioblastoma invasion by targeting glioblastoma-associated microglia via inhibition of the CSF-1R.
The study was funded by AACR-Amgen, Inc., Fellowship in Clinical/Translational Cancer Research (09-40-11 to SJ Coniglio); the Dana Foundation (SJ Coniglio, MH Symons and JE Segall), Association for International Cancer Research (AICR; SJ Coniglio and JE Segall), National Institutes of Health (PO1 CA 100324 to JE Segall and ER Stanley and P30 CA13330 and RO1 CA25604 to ER Stanley); and Voices Against Brain Cancer Foundation (MH Symons).
We thank Carl Manthey for helpful discussions on the use of JnJ, AstraZeneca and Johnson & Johnson for reagents, Plexxikon for PLX3397 and PLX5562, and the Segall, Condeelis, Cox and Hodgson labs for helpful comments. JE Segall is the Betty and Sheldon Feinberg Senior Faculty Scholar in Cancer Research.
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