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The coordination of complex tumor processes requires cells to rapidly modify their phenotype and is achieved by direct cell-cell communication through gap junction channels composed of connexins. Previous reports have suggested that gap junctions are tumor suppressive based on connexin 43 (Cx43), but this does not take into account differences in connexin-mediated ion selectivity and intercellular communication rate that drive gap junction diversity. We find that glioblastoma cancer stem cells (CSCs) possess functional gap junctions that can be targeted using clinically relevant compounds to reduce self-renewal and tumor growth. Our analysis reveals that CSCs express Cx46, while Cx43 is predominantly expressed in non-CSCs. During differentiation, Cx46 is reduced, while Cx43 is increased, and targeting Cx46 compromises CSC maintenance. The difference between Cx46 and Cx43 is reflected in elevated cell-cell communication and reduced resting membrane potential in CSCs. Our data demonstrate a pro-tumorigenic role for gap junctions that is dependent on connexin expression.

Summary: Different cancer cell compartments often communicate through soluble factors to facilitate tumor growth. Glioma stem cells (GSCs) are a subset of tumor cells that resist standard therapy to contribute to disease progression. How GSCs employ a distinct secretory program to communicate with and nurture each other over the nonstem tumor cell (NSTC) population is not well defined. Here, we show that GSCs preferentially secrete Sema3C and coordinately express PlexinA2/D1 receptors to activate Rac1/nuclear factor (NF)-κB signaling in an autocrine/paracrine loop to promote their own survival. Importantly, Sema3C is not expressed in neural progenitor cells (NPCs) or NSTCs. Disruption of Sema3C induced apoptosis of GSCs, but not NPCs or NSTCs, and suppressed tumor growth in orthotopic models of glioblastoma. Introduction of activated Rac1 rescued the Sema3C knockdown phenotype in vivo. Our study supports the targeting of Sema3C to break this GSC-specific autocrine/paracrine loop in order to improve glioblastoma treatment, potentially with a high therapeutic index. : Glioma stem cells (GSCs) have a high capacity for self-renewal, invasion, and survival. How they communicate with each other to survive and maintain their identity is not clear. Man et al. now show that GSCs have co-opted a neurodevelopmental program to activate Rac1 to promote defining features of GSCs.

Stem cells reside in niches that regulate the balance between self-renewal and differentiation. The identity of a stem cell is linked with the ability to interact with its niche through adhesion mechanisms. To identify targets that disrupt cancer stem cell (CSC) adhesion, we performed a flow cytometry screen on patient-derived glioblastoma (GBM) cells and identified junctional adhesion molecule A (JAM-A) as a CSC adhesion mechanism essential for self-renewal and tumor growth. JAM-A was dispensable for normal neural stem/progenitor cell (NPC) function, and JAM-A expression was reduced in normal brain versus GBM. Targeting JAM-A compromised the self-renewal of CSCs. JAM-A expression negatively correlated to GBM patient prognosis. Our results demonstrate that GBM-targeting strategies can be identified through screening adhesion receptors and JAM-A represents a mechanism for niche-driven CSC maintenance.