Systematic identification of molecular pathways driving GBM invasion

Glioblastoma multiforme (GBM) is the most prevalent and deadliest adult brain tumor. To systematically characterize the pathways governing brain invasion, we developed a three-dimensional (3D) ex vivo organotypic invasion model with clinical relevance to GBM. We used this model to enrich for highly invasive GBM cell population. Using next-generation sequencing to transcriptomically profile highly invasive and poorly invasive GBM cell populations, we have identified a network of extracellular matrix (ECM) components, including multiple collagens and collagen-interacting proteins, which are upregulated by invading GBM cells and strongly correlate in expression with clinical glioma progression outcomes. We identify the interferon regulatory factor 3 (IRF3) as a direct transcriptional repressor of ECM factors in GBM and show that IRF3 acts as an endogenous suppressor of GBM invasion. Therapeutic activation of IRF3 by inhibiting casein kinase 2 (CK2) -- a negative regulator of IRF3 phosphorylation -- downregulated the expression of ECM factors and suppressed GBM invasion in ex vivo and in vivo models across a panel of patient-derived GBM cell lines representative of the main molecular GBM subtypes in the clinic. Our findings illustrate an integrated and systematic approach for the discovery of novel pathways regulating brain tumor invasion and provide a strong mechanistic insight into the notorious, yet poorly understood, invasion capacity of GBM tumors. Overall design: Next-gen sequencing and mRNA transcriptome analysis on 2 independently derived highly invasive GBM cell populations (invasive clones 1 and 2) and 2 poorly invasive control populations (controls 1 and 2). U87 control 1 was analyzed together with and serves as a control for U87 invasive clone 1, and U87 control 2 was analyzed together with and serves as a control for U87 invasive clone 2.