Microglial Stimulation of Glioblastoma Invasion Involves Epidermal Growth Factor Receptor (EGFR) and Colony Stimulating Factor 1 Receptor (CSF-1R) Signaling

Salvatore J Coniglio,E Richard Stanley,Brian L West,Jeffrey E Segall,Marc H Symons,Eliseo Eugenin,Kostantin Dobrenis

doi:10.2119/molmed.2011.00217

Abstract

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.

Highlights

Glioblastoma multiformeremains one of the most difficult cancers to treat, with a median survival rate of 12 months after diagnosis [1,2]
We demonstrate a role for epidermal growth factor receptor (EGFR) and colony stimulating factor 1 receptor (CSF-1R) signaling during microglia-stimulated glioblastoma invasion
Consistent with our observations, it has been reported that glioblastoma specimens from human patients express CSF-1 and that expression of CSF-1 correlates with the degree of glioblastoma progression [22]

Summary

Introduction

Remains one of the most difficult cancers to treat, with a median survival rate of 12 months after diagnosis [1,2] This result is primarily because high-grade glioblastomas are highly locally invasive and, as a result, a relatively large population of invading cells is left behind after surgical resection [3]. Progress has been made in elucidating the genetic alterations and oncogenic signaling pathways responsible for glioblastoma, the molecular mechanisms of glioblastoma cell invasion are still largely undefined. It is becoming increasingly clear in the field of cancer biology that the tumor microenvironment, which includes stromal cells such as fibroblasts and cells of the immune system, plays a critical role in disease progression [4]. Tumor-associated macrophages are an important class of cells in the microenvironment that can potentiate carcinoma cell invasion and metastasis [5,6,7,8]

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Discussion

Conclusion